TROUBLESHOOTING HEAT PUMP SYSTEMS…REVERSING VALVES
Reference books will refer to compressors as the heart of refrigeration systems. If that’s the case, then the reversing valve would have to be the lungs, or liver, or kidneys of a heat pump system, for it is the component that determines whether the system runs in heat or cool…
The reversing valve may be a mystery to some. They are in fact, an assembly of two valves: the main valve which actually directs the refrigerant flow in the system, and a pilot valve which controls the main valve. The pilot valve applies system pressures to the ends of the main valve, suction pressure to one end, discharge pressure to the other, creating a pressure differential which will force the main valve plunger to slide in one direction or the other. This design allows the heat pump system pressures to actually switch the reversing valve position. A solenoid capable of switching the main valve directly would, no doubt, be very large. I’m oversimplifying the design and operation a little, but my intent is simply to summarize the function of the valve, because if it fails mechanically, your only option is replacement…an intimate knowledge of the inner workings turns out to be academic.
Valve failures will generally be 1) solenoid coil failure, 2) “stuck in heat or cool” position or 3) stuck somewhere between heat and cool positions. Coil failure is usually fixable. You only need to verify the absence or presence of coil voltage in the appropriate cycle, to eliminate wiring problems. Coils can short out or go open and in most cases, a new coil can be substituted.
Stuck valves could be the result of a pilot or main valve problem. In either case, I’ve had no luck in making a “repair”…In my personal opinion, “unsticking” a valve is only temporary…it will most likely stick again. I don’t recall ever seeing a valve stick one time only. But if you determine a stuck valve is the case, you can try freeing it by raising the head pressure. To do that simply electrically disable whichever fan motor is providing condenser air. If stuck in “cool”, the outdoor fan motor…if stuck in “heat”, the blower motor. I usually let the head pressure run up to 375-400 psi (R-22) or so. Obviously, this technique offers some inherent potential system hazards, so evaluate the entire situation carefully before you decide to do it. No advantage to creating a new problem, in attempting to correct another.
I’ve only seen a few cases of the valve stuck somewhere between cycles, which can be a difficult situation to diagnose. The valve plunger position may be such that the net result is a small amount of leakage between low and high side pressures. The symptoms will resemble a faulty compressor…high suction and low head pressures. The best way to diagnose the situation is measure “in” and “out” hot gas temperatures at the valve. If enough of the cooler suction vapor is mixing with the hot gas inside the valve, there will be a significant temperature difference between the compressor discharge gas and the reversing valve “outgoing” hot gas. And you could measure suction line temperature at the evaporator, then compare that to the “outlet” suction pressure tubing temperature at the valve body. What’s a normal temperature drop across the valve? It depends on where you measure of course, but from the few times I’ve actually checked, I’ll say 4 or 5 degrees max, with the higher differentials applying to the hot gas lines.
I’ve found reversing valves to be one of the more reliable components in heat pump systems. They generally perform their duties for many years, without failure. And when they do fail mechanically, it’s likely the result of some other system problem, such as continued operation with low charge, causing the valve to overheat and under lubricate…
February 19, 2008 at 7:51 pm
I recently troubleshot a Weather King and found a reversing valve fail in such a way that the exiting hot gas was going straight back to the suction side of the compressor. This problem ( I have never seen) was hard to find the suction pressure and discharge pressure were the same and the temp on the valve was the same . The only way I discovered it was the valve was to unsolder the discharge line and turn on the compressor. Have you ever seen this ?
February 19, 2008 at 8:41 pm
..yes, I’ve seen a few RV’s stuck somewhere in between “heat” and “cool”…creates a “short circuit” between the compressor discharge and suction…
February 21, 2008 at 11:12 pm
I have the same question Keith comments on. On a Lennox HP22-211 system, the suction and discharge pressures don’t change any as the compressor starts. The compressor makes normal sounds while running. In fact, the compressor sound changes typical of the first five seconds of operation.
The compressor then shut off promptly on internal the internal thermal switch. I tried switching between heat and cool modes in hopes of unsticking the reversing valve if it was stuck.
Is there anything short of removing the valve to diagnose if the compressor failed or the valve is in between? This problem started suddently during 20* outdoor temps.
February 22, 2008 at 8:51 am
..I’m not aware of any “non-invasive” method for diagnosing the reversing valve stuck in between heat and cool positions. Faulty compressors, in my experience, don’t generally trip the internal thermal switch “promptly”…which would suggest the RV is “short circuiting” the hot gas back to the compressor suction inlet. All I know to tell you is measure the reversing valve inlet and outlet tubing temperatures, and compare…which is probably not that easy to do. But if the hot gas inlet and constant suction outlet of the reversing valve are at or near the same temperatures, one would think the problem is in the valve. And you can try measuring temps away from the valve on what should be the suction or hot gas lines and see if there’s a significant difference…
This is all conjecture based on some assumptions, based on some limited information, with me attempting to visualize what you’re seeing…and I saw a similar situation to yours on an Armstrong unit. High and low pressures were about equal, although the compressor wasn’t tripping on the internal thermal…but I had nagging thoughts about the compressor being faulty, and wired it to run after removing it, and it appeared to be pumping ???
..and I helped a tech diagnose a similar situation that was the reversing valve…but in that particular case the leakage through the valve was small, and there was a differential between low and high pressures, and temperature measurements helped confirm the problem was the valve.
Unfortunately, there’s no simple method to diagnose the situation you’re talking about that I’m aware of…I’ve never done it, but you could crimp the compressor discharge line and install a schrader between the crimp and compressor discharge port. Then just “bump” the compressor and see what the pressure does…if it goes way up, that would eliminate the compressor as the problem…and that method obviously would entail a lot of time…
..you know, now that I think about it a minute, that’s a pretty good idea, even if I do say so…take one of those little rinkydink self-piercing valves and install it between the compressor and reversing valve on the hot gas line, at some point where you can come back later and repair the hole. Then, crimp the line between the piercing valve and reversing valve, again at a location allowing you to come back later and repair the crimp. Now,when the compressor starts, there’s nowhere for the gas to go, so with a gauge attached to the piercing valve, just “bump” the compressor on. If the pressure goes high, you’ve pretty much eliminated the compressor as being the problem… the piercing valve will simplify this process greatly and eliminate the need for refrigerant recovery. And since one or the other is faulty, coming back and correcting the pierced hole or crimped line won’t add that much work to the overall repair time…I’m glad I thought of that…
February 22, 2008 at 11:38 am
There was absolutely no warmth on the discharge line. The gauge connected right at the suction port didn’t move, not even a wiggle, when the compressor started. It is as though absolutely no refrigerant is flowing. That causes me to suspect the compressor. But I can’t imagine what would break catastrophically in a scroll unit such that there is no pressure differential when running. It seems like there isn’t much inside a scroll unit to go so wrong that there is no discharge pressure if the motor spins. I as sure from the sounds that the motor is spinning. It makes normal sounds, not just a hum.
If the RV was short circuiting discharge back to the suction, would the suction port fail to pump down at all? I understand why that would cause it to shut off on the thermal. What amazes me is the suction pressure doesn’t even wiggle the gauge at start-up. Can an RV handle so much volume when it’s stuck that no pressure would develop across it? All pipework is the same temperature as well. Suction and discharge lines at the compressor were both outdoor ambient.
February 22, 2008 at 4:07 pm
That is the same thing that happened to the unit I was working on except the compressor never tripped off. There was no change in pressure or temperature. The only way I found the reversing valve is to unsolder the discharge line from the compressor. That is a good Idea as Wayneshirley said you could unsolder the discharge line and solder in a fitting and check the compressor. I would do that over changing two compressors as I did.
February 22, 2008 at 4:51 pm
Larry…
A cool discharge line tells me the compressor is screwy. When you said it was tripping on the internal thermal, I assumed it was recirculating a lot of heat…maybe it tripped on over amperage? So far as trying to figure out what’s going on inside the Scroll…I wouldn’t care to guess, but they do fail…but again I ain’t there with you…try the piercing valve and crimp the discharge line…see what happens…
March 3, 2008 at 7:01 pm
I,m currently working on an old commandaire heat pump in an older condo ,the heat pump is about 15 years old and uses capillary tubes instead of an orfice or txv. the unit has been rebuilt including reversing valve,compressor,and reversible line dryer. there is only a tap on the suction side of the heat and cool, two total. this particular unit has a water backup holding tank and has no outside unit , basically it is installed in the wall and has the evaporator and compressor with all the other parts built into one stand alone unit. I,m having trouble getting it to heat the room above 63 degrees. Do you think it could be the RV , or just a pressure issue?
March 4, 2008 at 7:25 am
..I’m unfamiliar with the brand and design you’re working with, but the description of the unit leads me to believe it’s a water source heat pump…in which case the water tank would need some plumbing connected to keep the water circulating, or at least replaced with a fresh supply at some time intervals.
I can’t begin to offer any opinions based on the information you provide. If you can provide some system pressure measurements, refrigerant type and superheat measurement I might be able to make some conclusions. Knowing more about the water supply would be helpful…in the meantime, I’ll ask around about the brand and design…
March 4, 2008 at 8:38 am
..from what I could find out on short notice, the unit is a water source heat pump…but you’ll still have to provide more info before I can offer any intelligent comments about what might or might not be the problem…
March 4, 2008 at 12:37 pm
..from what I gathered in talking with a friend who has serviced some of the units, it’s most likely a closed loop “geo-thermal” system with a de-superheater pre-heating the condo hot water supply, which explains the “back-up water tank” you mention.
March 4, 2008 at 4:46 pm
The condo has a huge electric boiler which feeds all the units, When I pulled the unit out to service it I noticed it had spirovents on the supply and return water pipes which I thought was unusual, I ended up taking them off and found they were both plugged solid with small metal fragments and a ton of black pudding like goo which i would imagine is bacteria from the water/glycol in the system. I guess the boiler shut down recently and the last time it was serviced ( last srvice on record) was 15 years ago. I cleaned out the water lines and flushed the holding tank but there is still a possibility I didnt get all that gunk out of the tank. I am going back tommorow 3/5/08 to check it out again and I will tell you what the pressures are when I find out. I know that trane makes a retro unit for this application, its a little bit larger in size and more efficient, the problem is I cant get one yet, apparently I can order one but it would take about 5 months to get in says the supply house. Im not sure if it has something to do with the fact that american standard bought out trane or not.
March 4, 2008 at 11:15 pm
…Paul, you know more about that particular unit than me. With the exception of a couple of open loop water source heat pumps my experience is all air-to-air. If you’re familiar with heat pumps in general, then you can troubleshoot the one you’re working with…but I look forward to seeing some system pressures, and whatever else you can measure in the way of operating data.
March 5, 2008 at 6:58 pm
I went back to that heat pump job today and found the unit working fine, the home owner wasnt giving me the right info. when he left a voicemail. when i arrived the room was reading 70 degrees, i had about 80psi on my suction and 300psi on the liquid which seems high. being in the northeast i dont have a whole lot of expierience with many heat pumps. what i did find was his heat anticipator burnt out on the t-stat and the tempurature was over shooting buy about six degrees. other than that the air temp. differential seemed fine, it was 20 degrees buy my digital thermometer. i dont know if this helps you with anything but i wanted to tell you nontheless.
March 5, 2008 at 7:50 pm
..the pressures eliminate any compressor or reversing valve problems. As you say, 300 psi is probably on the high side for the discharge pressure, and 80 sounds high for the suction, at least on air-to-air stuff…but, not knowing anything about the unit, I’m reluctant to say for certain. If they are high, the problem is likely a dirty indoor coil, or overcharge…You’ll have to check superheat and subcooling to get a better idea of which is the problem. I have no idea what the “design” values would be for that particular unit, but 10-15 degrees for either would be reasonable “standards”…the superheat will probably be low in either case if the glycol heat exchanger is cap tube fed, but if the subcooling is a lot higher than 15, I’d go with over charge…that would also be a good guess, since all the repair work has been done…the previous tech(s), if not careful, could have easily overcharged the system…
March 14, 2008 at 6:45 pm
Thank you for your input I really appreciate it. I have to go back anyway, the homeowner tried to put in a new t-stat and couldnt get it to work so i’ll bring my recovery equipment this time just incase.
March 14, 2008 at 8:44 pm
..let me know what you find out…
July 1, 2008 at 7:49 pm
I have a 1 and 1/2 year old Goodman heat pump, I started it up this summer and left for the day came back and it was froze up put on my gauges and had 120 on suction and 105 on the discharge side, we replaced the compressor still same problem then with help from another tech we replaced the compressor again and the 4 way valve, Still same Problem talked with another tech and we thought the Coil was plugged so we replaced it Still same problem, so now I will try putting a service port on discharge side of compressor betweem compressor and 4 way valve like you mentioned on someoneelses in the forum, but I am running out of things to replace, any help that you can give I would love it
July 4, 2008 at 9:04 am
..my, my, my…what a mess… Your lack of knowledge in regard to heat pumps and mechanical refrigeration is painfully obvious. The two items you chose to replace are the least likely components to fail and the least likely causes of icing…it’s most often the result of low charge or low airflow…the pressures you reported are a physical impossibility…before doing anything further, I would suggest you call someone who can accurately analyze and diagnose the system…
July 16, 2008 at 3:48 pm
I have a 1.50 ton BRYANT to day comp. runs would not pump . I was sure it was a dead comp. Started checking pressures . bored hole in suction line going in comp. cut discharge line in to blew air through line air came out suction line . found prob. 4 way valve stuck half way.
The home owner did not want to change valve I bypassed the valve with new suction line charge it up . He has cooling only no heat pump.
If this was not a close friend i would not took these actions .
July 16, 2008 at 6:15 pm
..sometimes you do what you have to do…
July 28, 2008 at 8:51 am
I have a coleman heat pump mod#drh04021cd ser#980247821 , unit not cooling, I stopped by the job and my gauge pressures where 10 psi suction and 125 psi head. I thought there was a leak on the unit so I recoverd the refrigerant that was in the unit 6.5 lbs. (Which was strange). Then pressurized the unit to 150 psi with nitrogen, I checked unit for leaks and found none, released the nitrogen charge and evacuated unit, added refrigerant and unit is now running at 75 psi suction 45 degrees, 225 head 110 degrees, unit is cycling on temp. Is it possible the reversing valve was stuck?.
July 28, 2008 at 7:30 pm
..I’m fond of saying anything’s possible, but low suction usually isn’t symptomatic of a stuck reversing valve…least ways, not the ones I’ve seen. If a reversing valve is stuck somewhere between “heat” or “cool” positions, the high pressure bleeds into the suction portion of the refrigerant circuit, which would raise the low side pressure…
The numbers you measured make me think more in terms of a liquid line restriction or “stuck” TXV. A subcooling measurement during the same time, would have provided some more information as to what was going on, and probably eliminated your first thought of low charge and leak…It is surprising the problem fixed itself after removing the charge and evacuating the system. But I’ve seen a few occasions where a new system with TXV acts weird on the initial start-up and then gets normal…like I say, most anything is possible.
August 1, 2008 at 1:23 am
I have a air cooled HP, I just replaced the RV and my pressures are terrible. Low side goes on vac and high doen’t move.
I checked the orfices for any possible restriction and were clear, I have replaced the liquid dryer and nothing happen.
My guess is I may have a restriction on the suction side probably on the accumulator, because I don’t have any liquid come back to the evaporator coil or the condenser.
Any sugestions about this problem.
August 1, 2008 at 7:13 am
..accumulators don’t generally restrict, because they are essentially a tank, used to trap and vaporize any liquid that might be in the return portion of the system, preventing it from entering the compressor…suction side restrictions in general, are rare occurrences, with residential equipment. I’ve seen a couple of restricted suction line filters. But if the low side is going into a vacuum, and the head doesn’t move, something is definitely blocked. What is the high side reading?
What were the original symptoms than prompted you to replace the reversing valve? If there were no restrictions before, there shouldn’t be any afterwards. Were you careful replacing the RV? they are easily damaged by heat. Worse case scenario would be a melt down of the internal piece that could block flow through the valve. Assuming your pressures are in the “cool” cycle, have you tried running the system in “heat” to see what the pressures do? where are you measuring the pressures… service valves or at the constant suction tap? Are the service valves by chance closed?
August 20, 2008 at 2:18 pm
I have a xr1200 trane heat pump when it calls for cooling unit runs great discharging 57 deg, air from registers then anywhere between 20 minutes to 5 hours unit starts to discharge 80 degree air from register. replaced coil and defrost board. if i pull one lead off of coil and put it back on goes into cooling and works great for another 20 minutes to 5 hours i am really starting to pull my hair out the only thing i can think to do next is change reversing valve
August 20, 2008 at 3:57 pm
..are you saying the rev valve is switching to heat? if so, the problem could be as simple as a loose wire nut connection on the low voltage wiring where the stat wires are spliced to the factory wires…they are usually orange. Check that. If it seems good, try wiring the orange and red wire connections together. That will keep the rev valve energized continuously. If the problem disappears, you’ve eliminated the reversing valve as the culprit. If not, respond back.
December 8, 2008 at 8:48 pm
Hey Wayne…great website! I have a 1 year old Goodman heatpump 15 SEER. Everything has been working great until two weeks ago. We switched from cooling to auxilliary heat and the condensing unit would not come on. It would try for approximately 2-3 seconds and then shut down. I then switched the thermostat back to cooling and the unit ran great. I then swithched it back to auxilliary heat and the unit came on for approximately 20 seconds and then it would shut down for 10 seconds, then it would come on again…the process continued. The lines got hot and house was warming up, but I shut it down. I was afraid it wasn’t good on the compressor. It is currently in emergency heat and it works as well. I checked the inside coil, it’s clean…the outside unit is clean and I added an additional return air, to no avail. I am assuming it is a high pressure switch shutting it down, but would it do the same in cooling mode? The tech said it was not overcharged.
Could it be: the capacitor? a relay?
I even tried a new defrost board and thermostat…same thing happens.
December 8, 2008 at 10:44 pm
First of all, I’m not familiar with Goodman 15 SEER heat pumps, so there may be something in the design I’m not aware of…if it runs in cool mode, any electrical issues would normally be ruled out as the cause of a heat mode problem. The only difference in cool and heat is the reversing valve position and refrigerant flow. A high pressure switch opening up is a good guess, but without some numbers there’s no way to know for sure…and no, high head pressure in the heat cycle can occur without high head in the cool cycle…there could be some sort of restriction at the indoor coil metering device, but again you need some system pressure readings…if the equipment is only a year old, why can’t / don’t you get the installer out to diagnose the problem?
December 14, 2008 at 10:36 am
is it possible that you can make the switch on a reversing valve by placing a large magnet next to the valve?
December 14, 2008 at 7:23 pm
..I guess most anything is possible…
December 21, 2008 at 9:42 am
I have a heat pump system when cold weather the system will run constate and not much heat comes out. Some times when system changes sounds like a noise out side at unit. If it gets in low temp this will run all the time. Now it has run for a 3 days not shut off. Nights heat drops no matter what temp i have set in house. I set on 70 and when I go up thismorning it said 63 . What happened?
December 21, 2008 at 11:14 am
..the heating capacity of heat pumps decreases with decreases in outdoor temperatures…it’s the nature of heat pumps. For example, a 3 ton heat pump will deliver about 36,000 Btu’s of heat when the outdoor temp is 50 F. But at 20 degrees F, the heat output will drop to some value approaching 25,000 Btu’s.
How well the system will maintain the thermostat set-point will depend on the outdoor temperature, the tonnage of the unit and the heat loss characteristics of your home, which depends on how “tight” the house is as well as the amount of insulation. But, the system “auxiliary” or back-up heat source is supposed to kick in, when the heat pump can’t maintain the set point…second stage heat is the terminology, which is usually electric resistance heaters or gas furnace. In that situation the room temp should maintain within 2 or 3 degrees of the thermostat set point.
Based solely on the information you provided, I would guess there is some problem with your heat pump system…but I can’t diagnosis it from where I sit. Below is a list of some of the more common / possible ailments:
1) low on “freon”
2) condensing section not defrosting
3) condensing section fan not running
4) faulty second stage heat / controls
5) reversing valve/compressor problem
You’ll have to call a service company/person or at the very least, someone who is familiar with heat pump technology and has the test instruments to make an analysis/diagnosis.
December 21, 2008 at 1:49 pm
Great info on the TXV diagnostics. I am thinking about a second opinion now my service person said I need it replaced after looking at the pressure and manually operating the solenoid. It was just as we were leaving for family hoilday visit so I have not done anything yet.
Symptons.. Outside Unit (Amana about 6 years old) Starte and stopped in only a second or two on a Sat. I turned off the unit to call the repairman on Monday. Monday morning was warmer but I turned on the unit and it ran normal. I called repairman anyway.. recommended I wait and call while malfunction is happening. Next day it was colder and it occurred again. I called the repairman again and later that day is when he put the gauge on. First comment was its a little low on pressure… then manually tripped the solenoid saw high pressure and very low low pressure and said I need a new TXV no other diagnostics. The txv valve was frosted over. A bit of freon was lost here because all the fittings were loose .. I am wondering if the pressure to operate was higher on the warmer day resulting in a possible rason it ran all day and addinga pound or two of freon would be a worthwhile alternative test before draining all the freon and replacing the valve… then new freon. I have not seen their estimate yet but he guessed 12-15 hundred for parts labor and freon.. 4 ton unit. ouch
December 21, 2008 at 7:08 pm
I can’t make any conclusions based on the limited information in your comment. But if the system has lost refrigerant and the tech didn’t add any, I would question the diagnosis…a frosted TXV could mean a faulty TXV, but could also mean undercharge of refrigerant or something else…and why are they charging you for “new” refrigerant in the estimate?…whatever amount of refrigerant remaining in the system can be recovered and returned to the system…You can decide about the second opinion…
December 22, 2008 at 12:28 pm
The repairman said that the refrigerant could not be recovered by law?? The pressure reading of refrigerant was ‘a liitle low’ was the comment and when I said lost coolant it was just a few seconds of running out because loose fitting on the gauge… he freezer burned his hand closing it. Thanks for your prompt reply. I will try and look up the pressures for normal reading when the compressor is not ruuning to gauge whether low or not. Great Web Site Thanks again
December 22, 2008 at 5:04 pm
..Hell, by law refrigerant has to be recovered…it’s either recovered or vented to atmosphere…venting is unlawful…
December 25, 2008 at 1:28 pm
Great website……..I retired several years ago from the business, before heatpumps really caught on. My family members usually ask me to help them with conditioning their air problems. This site is a great place to pick up tips that us older folks missed out on. Keep em” comin”.
December 31, 2008 at 7:22 am
Units installed in Condo 2003. We moved in Apt. fall of 2004.
Heat Pump mfg. by FHP Manufacturing
Geothermal water circulated through building
Listed Heat Pump Cooling A27 Heating A20 Model GTO1O-1VTC.
Blower 0.10 hp Loop Pump 1/6 hp
R22 Refrigerant 26 oz 1 circuit. Thermostatic expansion valve, reversing valve.
Compressor 230 v 1 ph 4RLA 35LRA Design Pressure 450 psi High 150 psi Low
Unit doesn’t heat hardly at all. Compressor runs almost continually. Condenser coil is fairly warm to the touch.
December 31, 2008 at 8:07 am
..the facts you provided don’t offer any information as to how the system is operating or if there might be a problem…analysis/diagnosis requires system pressures, superheat/subcooling values…
January 2, 2009 at 4:15 pm
I have a trane hp model TWN030C100A0 . The unit works great in the cooling mode over the summer and works great in cool weather as long as the outside temp is above 37F. Around 36 degrees F outdoor temp it switches over to cool air output and I have to switch it over to emergency for the heat strips to operate for the nite. The next day as soon as the outside temp rises above 40-41 degrees F I can switch the thermostat back from “emerg heat” to “heat” and it heats great. I have replaced the rev valve coil and the wiring from the unit under the house out to the hp in the last year with no change in performance. What are the chances this is a rev valve problem?
January 2, 2009 at 4:52 pm
..the symptoms you give are strange to say the least. Reversing valves don’t know what the temperature is, unless some control is telling them it is at some value, and even then logic would dictate no control would switch the reversing valve to “cool” because the outdoor temperature dropped below some value…there are some controls that will shut down completely the outside unit at very low temperatures, or at least temps well below the 36 F you mention. Most “stock” equipment doesn’t have any extra controls installed…
The only remote possibility I can think of at the moment causing the symptoms is the defrost control…it could be initiating a defrost cycle (which is essentially “cool” mode) and then not terminating the defrost…but the defrost control is supposed to energize the strip/aux heat too, which would eliminate the cold discharge air…and it’s possible the reversing valve could be sticking in the “cool” position after a defrost cycle…you’ll have to do some investigation or call a service man to investigate during the time the system is acting strange…it’s difficult to diagnose without some measurements and/or observations…
January 2, 2009 at 6:04 pm
I should have added that when the hp is putting out cool air in the heat mode, the aux heat green light does come on but the air stays as cool as if ac is on. Also, the hp has never switched from heat to cool during a run cycle. Thanks so much for your reply and I certainly appreciate how difficult it would be to diagnose this problem.
January 3, 2009 at 8:06 am
Has it always done this or just started?
The fact that the aux heat light comes on tells us either the second stage switch in the stat is closing or the defrost control is energizing the aux heat light…next time you see the situation occurring, touch the larger copper tube with your hand for warm or cool feel…and be careful as it may be hot…
January 3, 2009 at 10:03 pm
I have a heatpump that is 401a, it operates good in cooling with good pressures, but as I put the unit in heating the head pressure goes to 510 with the suction in 300 psi what would cause the head pressure to be so high.
January 4, 2009 at 9:46 am
..you mean 410A, right?..high head pressure is almost invariably due to overcharge or low condenser air (in the heat mode, the indoor coil is the condenser). But since the system “operates good in cooling”, low airflow at the indoor coil would seem unlikely…but on the other hand, if the system is fixed orifice metering and it appears to be so, low indoor coil air flow symptoms in the cool cycle can be offset to some degree by overcharging…so, I would guess the problem is overcharge…and I emphasize “guess”…system pressures alone aren’t enough to make an accurate diagnosis..
January 7, 2009 at 4:03 am
fairly new to heat pumps…worked with them for months now. so my issues….they are climate master tranquility series heat pumps. i keep getting these “low air coil temp faults” so i hook up gauges and my pressures are pretty low in cool mode (R-410A). so then i cycle the unit into heat and run it for about 10-20 min. then cycle back to cool and my pressures are where i want them to be. could it be a bad rv? my temps across the rv is good. you guys ran into any issues like this? thanks….
January 7, 2009 at 8:35 am
I’m not familiar with the brand/model you mention or the fault code. I’m assuming the “low air coil temp fault” is referring to the indoor coil and guessing the cause is most likely low airflow across/through the coil…low suction pressures are most often the result of low airflow or low charge…if the superheat is also low, that would confirm low airflow…if you can provide more system info (pressures, superheat, subcooling, type metering device) I may can offer more of an answer…
January 13, 2009 at 8:42 pm
I have a through the wall heat pump unit says it has a charge of 24 ounces but it won’t work. The compressor ran hot and I added more freon until the comppessor cooled down and the pressure went up. It seems to be working now but is this just a temporary fix or will it harm the compressor?
January 13, 2009 at 10:03 pm
..it’s most likely temporary in the sense you’ll have to add some more at a later date…The fact it needed refrigerant added means it probably has a leak, and leaks rarely correct themselves…
January 16, 2009 at 2:07 am
I installed a heat pump in the spring, worked good in cool, then about October it just couldn’t keep up in heat. OAT now is 35 degrees and my pressures (R22) are 185psi & 48psi. I’m only getting a 10degree rise on the indoor coil. HP is 2.5ton fixed orifice, indoor coil is 3ton with txv. Charge is good, but when I checked my temps my suction line is 27 degrees, discharge line off the compressor is only 76degrees. What would cause such a low discharge temp with those pressures?
January 16, 2009 at 8:15 am
..the pressures look about right for 35 OAT. 185 head corresponds to a condensing temp around 95, so 76 discharge isn’t realistic…the compressor discharge temp can’t be less than the condensing temp…
..where are you measuring the temps to arrive at the 10 deg rise across the coil?
..a 3 ton indoor coil means your system is circulating 3 tons worth of air. The outdoor unit is only 2.5 tons, which could result in a low temp rise across the indoor coil…
January 16, 2009 at 10:04 am
That’s what keeps messing me up. This system is defying logic. The coil measurements were taken at the filter rack on the return air of the furnace and about 12-18″ past the coil. I checked duct static, it’s good. But the discharge temp is definitely less than the condensing temp. I can grab the discharge line right at the compressor and hold on to it!?
January 16, 2009 at 10:38 am
..that’s interesting. What kind of temp differentials are you getting across the reversing valve with the 2 “hot” and 2 “cold” circuits?
January 16, 2009 at 12:24 pm
Temps across the valve look fine. Today is 31 OAT and readings are as follows:
93.7degrees into RV 215psi
88.8degrees out RV
25.7degrees into RV 57psi
25.3degrees out RV
Still confused as to how/why my discharge temp is less than my condensed temp. Indoor coil air in 64, air out 77.
January 16, 2009 at 12:33 pm
should be 47psi not 57psi
January 16, 2009 at 9:04 pm
..I just realized the system superheat at the rev valve is a big “0″ degrees..15-20 F closer to normal for a fixed orifice coil…you sure the system isn’t way the hell overcharged? measure the liquid line temp at the service valve and calculate subcooling…20-30 F would be reasonable. You used the word furnace…is your system a dual (hybrid) fuel system? Are you taking all these measurements after the system has had time to level out at steady state? what are you using to measure tubing temps? Type K with good contact to the tubing? are the suction lines showing any indication of frosting?
January 16, 2009 at 9:08 pm
..another question. When the new condenser was installed, was the charge adjusted to subcooling or beer can cold or what? It’s easy to overcharge a TXV indoor coil in the cooling cycle…
January 31, 2009 at 10:09 pm
new armstrong heat pump i just installed stuck in ac mode. pull 24 volt lead off board to reversing valve and it switches to heating where i need to be. seems unit is stuck in cooling mode all the time until i do this charge seems find and ichecked my th8000stat to make sure we were energizing reversing valve in cooling mode . i have 24 volts to reversing valve no matter if i,m set for cooling or heating. do you think the board in outdoor unit is letting 24 volts go to reversing valve at alltimes.
February 1, 2009 at 7:59 am
Anything’s possible…did it ever switch on a call for heat by the thermostat?
February 3, 2009 at 2:16 pm
Great website! I have a problem with multiple heat pumps. I had 60 units installed two years ago in a apartment community. They are AeroSys through the wall heat pumps mated to a ICP air handler, both 1.5 ton ratings. They were professionally sized for the application and ductwork and the heat pumps are TXV controlled. The problem is reversing valves that shift slowly and noisily and sometimes stick half way. They make a very annoying windmilling noise and can be unstuck with a tap on the valve. We have had 43 of the 60 units stick, some multiple times. The first year I had 21 stick and the manufacturer came out to check them and sent a crew to replace the 21 valves. (note: I noticed no nitrogen introduced while brazing). Operation in AC is perfect and the valves are energized for cooling. Second winter brings failures again. Manufacturer states that it is my problem and either a problem with intall or air handler. So I hire a tech to come out and we replace 10 of the faulty valves (some of which were already replaced by the manufacturer). I sent two valves back to Ranco for analysis and nothing found faulty. I had the refrigerant tested and came back fairly normal. We installed saddle taps on either side of a valve that was frequently sticking and you can watch the pressures equalize as the valve slowly slid and stopped. Tap on it, it finishes shifting and is fine, shifts back to heating with no drama. I talked to the valve engineer that does failure analysis for Ranco and he suggested a valve rated for a .75 ton unit that has a smaller bore and would shift faster.. To mickey mouse for me and to expensive. The units heat and cool well. I suspected charging issues as all units needed to have refrigerant added on installation to get the superheat right. The manufacturer reccomended charge is about a pound light from what the units seem to want according to the installer. I even tried reclaiming and charging to manufacturer specs on a couple units that are problematic with no change in results. I also flushed and deep evacuated these units and replaced the filter-dryers as well. I have had 5 of the ten I replaced stick, some multiple times, I also cut open and examined 4 replaced vavles and could find nothing wrong with them. The sticking problem seems to be temperature (30-35F) and high humidity dependent. Some valves that would stick repeatedly will all of a sudden be fine for weeks?? I also started insulating the problem reversing valves by wrapping with insulation tape after a suggestion that maybe the capillary tubes on the valves sometimes get to much oil in them and with the cold weather they cause sluggish shifting. That has seemed to help but not eliminate the issue. I am at wits end! Keep in mind that roughly 1/3 of the units installed have not failed. Maybe the valve and compressor is flooding sometimes? Lots of noise when reverse occurs. Sorry for the long post. Any ideas? Thanks, Paul.
February 3, 2009 at 4:29 pm
..67% failure rate…41 in 2 years. That’s about 20 more than I’ve seen in 25 years!!! The few failures I’ve seen could be inferentially blamed on old age or overheating/under-lubricating due to some other problem with the system like low charge. And all the ones I’ve replaced subsequently performed as designed.
Needless to say, there’s something going on, but I can’t begin to guess as to what it might be specifically. External conditions, temp and humidity, shouldn’t affect the valve performance normally. I could see where extreme liquid flooding for extended periods might create a problem, but that’s an equipment operating issue. Oil clogged capillary tubes…???
Are the systems R-22 or R-410A? Were the ICP air-handlers an “approved” match for the AeroSys C/U’s? Are system pressures, superheat/subcooling values normal?
February 3, 2009 at 8:56 pm
systems are R-22, there were no reccomendations for air handlers by the manufacturer. The supplier matched components and they are a large high volume HVAC supply house. I know the pressures are good and superheat and subcooling have been good when checked. ( I have not personally witnessed the temperature readings, just looking over shoulders). The intermittant nature makes it difficult for any meaningful testing as well. The capillary tube comment came from a major manufacturers field troubleshooter and apparently was something they came across at some point. There is a TXV in the air handler and in the outdoor unit, maybe some check valve issues? Thanks for your time, Paul.
February 3, 2009 at 10:23 pm
I’m asking around…but for the moment I don’t see an obvious cause from where I sit. The Ranco guy is the expert…but did you pay any attention to the physical size of the valves? The smallest valve I can buy is rated for .75-1.5 ton R-22 with 1/2″ and 3/8″ tubing…you can’t get much smaller than that…check back in a day or so for anything I might have found out…
February 4, 2009 at 7:41 am
I procured one of those small valves and it would require adaptors to size down to it and I am not comfortable doing that. I also suspect that could be trouble come summer. The pressures before defrost is called are fine, plenty to shift the valve according to specs and the Ranco guy, but his comment was more along the line of it could be a volume not pressure issue? More info: the air handler is stacked directly above the outdoor unit in a HVAC closet with the outdoor unit coil in an opening in the wall that is maybe 30″ by 24″. The line set exits the top of the air handler and drops straight down to the outdoor unit and is maybe 7 feet in lenght. I think the oil charge that the scroll compressor comes with is for 20 or 25 feet. A link to the manufacture: http://www.aerosysinc.com/Literature/THHP%20Sales%20LIT%201008.pdf The units we have do not have an accumulator as shown in the photo. Thanks again for mulling this over. Paul
February 4, 2009 at 8:43 am
..I’m going to send you an email…
February 11, 2009 at 6:24 pm
Can anyone briefly explain the operation of a piston type expansion device when a heat pump is in the heating mode. Does the piston move, does the liquid referigerant pass around the outer openings or thru the orifice………what really goes on. I guess these things work since so many are used. THANKS IN ADVANCE.
February 12, 2009 at 1:12 am
..most piston devices are bi-flow. When liquid is entering the coil, it passes through the orifice…when hot gas is exiting the coil, it flows around the piston…the piston shifts position a little to accommodate the direction of flow and needed function…
February 20, 2009 at 8:12 am
I have often heard comments that the installation of a reversing valve diminishes the cooling capacity of an air conditioner. Today I saw proof of what is happening. On a window unit with a new R-22 compressor recently installed, the evaporator return to the compressor was rising 9ºF from where it entered the reversing valve to where it exited. The culprit is the compressor discharge which is heating the reversing valve. Is this common in reversing valves that there is heat transfer between the hot and cold refrigerant flows? Is there any way to avoid this?
February 20, 2009 at 8:44 am
..I assume you’re talking about a window unit heat pump? The temperature rise you describe would more likely be due to a malfunctioning reversing valve, allowing hot discharge gas to mix with the return gas in the suction line…there is normally a small amount of heat transfer between “hot and cold refrigerant flows” but nothing like you suggest…
February 20, 2009 at 10:13 am
..well, I may have misread your comment…A 9 degree rise may be normal or close to normal…I haven’t done a lot of research in the temp rise through the reversing valve, but I have noticed in some cases, it can vary with system charge…I believe 9F is a little high for normal, at least with central system equipment…whatever the heat transfer inefficiencies might be, the designers no doubt took the factor into consideration…
March 11, 2009 at 3:02 pm
Hello There!
I have a McQuay Int Water source heat pump. M#WMH012CMNR Date:1997. Cooling Cycle:Discharge Temp: 45 degrees 75 Psi, Suction Temp 45 degrees 75Psi. Leaving Rev Valve to Condensor Temp 113 degrees. Leaving Rev Valve to Comon Suction Line Temp 165 degrees. Leaving Evap Coil Temp 70 degrees . From Rev Valve to Evap Coil Temp 155 degrees .
Any Information would be mostly appreciated.
Thanks
HVAC Brother, from another mother.
March 11, 2009 at 4:54 pm
Can you just tell me what the suction pressure, head pressure, superheat and subcooling values are for the moment? and what’s the question…system not cooling?
March 12, 2009 at 9:12 am
Its not cooling or heating. I turned it off for now. Both Suction And Head Pressure are 75 psi.
Thanks
HVAC Brother, from another mother.
March 12, 2009 at 1:44 pm
..obviously if both pressures are the same, the compressor or reversing valve is screwed up. If however, you’re measuring 165 F tubing somewhere, I would think the compressor is doing some pumping. Certainly, if the suction pressure is 75 psi and the suction line is the 165 F, it would seem the hot discharge gas is by-passing inside the reversing valve…but my not being able to see the pressure take-off points, temp measurement locations or piping in general, there may be something I’m missing…
April 5, 2009 at 8:06 am
Not sure about doing this job, may have sp. prob. friend twisting my leg.He has a 1200 sq. ft house on slab. He does not want air handler in atic, He wants hp. pack on back side of house on a slab. I will have to push air up 8 ft.across atic 20 ft supply 14 ” flex into distr. box 22×22x48 3 8″ outlets for flex on both sides 2 on top longest branch run 15 ft. 2 1/2 ton pack hp. may use intertherm for more air flow what do you think ?
ps have not done mush cal. yet . thanks
April 5, 2009 at 8:18 am
On post just made, I am sure it would help to use 14′ hard pipe right ?
April 5, 2009 at 12:48 pm
Ductwork in residential applications is usually sized for static/friction losses based on total equivalent length (TEL) and available static pressure (ASP). It’s a simple method for low pressure systems. But, it isn’t my strong suite, so I don’t have any “empirical” formulas to offer. I can say arbitrary sizes chosen before doing the calculations can lead to airflow problems…14″ metal pipe will carry 1000 cfm (2.5 tons) at a respectable friction loss per 100 linear feet. But, depending on the TEL, it might not be respectable enough. You have to refer to Manual D and go though the calculations to be reasonably safe/accurate in sizing the ducting…
June 12, 2009 at 6:47 am
Hi Wayne,
Got an issue with an 8 year old Trane TWA090 heat pump split. I wans’t getting voltage to RV (which has been replaced by other’s 2 weeks ago) So I jumped thru r o to direct volt to it. Instead of hot liquid coming out of reversing valve it is cold going into the outside condensor coil and then will start to freeze abit txv tubes, on top of that the suction side get’s very hot as if it were in heat mode. Any suggestion’s? Suction is at 175 liquid is at 145.
June 12, 2009 at 5:51 pm
yep, sounds like it’s running in heat mode, and sounds like you may have the gauges connected to the service valves, in which case both are high pressure…
June 23, 2009 at 6:02 pm
I have a 4.5 year old Goodman CPLE30-1A Heat Pump in a 1600 SF, 2-story house in Georgia. I know it is undersized, I fought with the builder and his AC sub for 2 years and all they ever did was change out some of the registers and wrap the unit in the attic with more insulation. On a hot summer day the best we can hope for is for the upstairs to hold at 80.
Anyway a couple of months ago we had a chilly night and we turned the system from cool to heat. Turned it back to cool the next day and the following day the system just started blowing hot air on it’s own. I turned it off, let it sit for a few hours and when I turned it back on it was blowing cold again.
A few days ago we went upstairs to go to bed and we noticed the smell that you get in the winter when the heat is on and the system was blowing hot air. Turned it off, let it sit for a few minutes and turned it back on. Blowing cool again.
When we woke up this morning it felt stuffy and I found that it was blowing heat again. I called a service tech that I trust to come out and he said that my system was operating the best it could but that since we have a “zoned” system (1 thermostat for each level of the house, both controlling a single heat pump) that when the temp dropped below the thermostat setting the heat would come on. He recommended that I have someone disable the “zoned” operation.
We left the AC on 70 all day knowing it would never get there and when I got home it was 74 down/76 up which I was very happy with. About 30 minutes later it started blowing heat agian. Turned it off, let it sit for 30 minutes and turned it back on. It’s blowing cold again.
It just seems really weird for the system to be blowing cool all day and all of a sudden flip over to blowing hot air. Could this be caused by some sort of problem with the reversing valve?
June 23, 2009 at 9:31 pm
I would be inclined to think there was something electrical going on with the reversing valve. Your brand, like the majority of brands, energizes the reversing valve solenoid in “cool”. If the solenoid loses voltage for some reason, the system will kick into heat mode…what might be causing it intermittently isn’t quite as easy to say…
The few times I’ve seen similar situations, the problem was a simple loose wire-nut connection made up at the outdoor unit with factory and field wired stat cable. There is another connection at the air-handler most likely. My experience with zone controls is virtually non-existent, but I would think it is a possibility…having a tech there when the issue is taking place would be nice, since some voltage measurements could be made and possibly find where the glitch is coming from.
June 25, 2009 at 10:02 am
Thanks. It happened again last night. System ran pretty cool all day and at about 11 pm it started blowing warm. We turned both thermostats to OFF but left the fans set to ON instead of AUTO. Woke up this morning and there was hot air coming out of the vents and it was 88 degrees inside the house.
July 1, 2009 at 6:27 pm
why should the heat pump not be operated above 65 degrees for long periods of time in the heating mode?
July 2, 2009 at 5:26 pm
why would a manufacturer use line voltage for a four way valve coil when a 24 volt could be used?
July 3, 2009 at 7:59 am
..I started learning service in the early 80’s. The heat pumps I dealt with at that time were manufactured in the 70’s, maybe even the 60’s. Most, if not all, had reversing valves with 240 volt coils…
I can only guess the electrical designers started out with a mentality the RV coils needed to, or should be, 240 volt, or maybe the valve design was such that a lot of electrical “power” was required for the valve to switch, or there may have been some other explanation for the voltage design…I don’t know anything about equipment “design”.
Early heat pumps were pretty much void of solid state (electronic) components…it was all electro-mechanical: relays and mechanical timers. Once solid state defrost controls became available, the entire “controls logic” could be greatly simplified. Where the old units needed a “heat relay” to switch the reversing valve, and a “defrost relay” to accomplish a defrost cycle ( switch the valve, energize the strip/aux heat and de-energize the outdoor fan), the solid state “board” could accomplish the same thing, as well as sense the need for a defrost cycle. The 24 volt coil may have simply been the logical result/product of design refinement…
July 1, 2009 at 6:28 pm
Why should a heat pump not be operated above 65 degrees for long periods of time in the heating mode ?
July 2, 2009 at 5:29 pm
Thank you for your help , we are doing research for our mid-term exam, some of this info is hard to find if you are a rookie
July 1, 2009 at 7:29 pm
..if the desired indoor temp is typical, 70 +/-, a heat pump wouldn’t run very long per cycle, when the OD is 65+…If someone is after 80 F indoor temp, yeah it might run a while…and then there are the few oddballs who run the system in cool when the OD is 65…
As outdoor temps increase, there is more heat available for the outdoor coil to extract and transfer to the indoor coil. The more heat transferred to the indoor coil, the higher the head pressures will be. The constant volume of air flow through the indoor coil can only remove so much heat from the refrigerant, resulting in higher condensing temperatures. I doubt the designers factored in a lot of heat cycle operation at 65+ OD temps.
But to answer your question, the higher head pressures put a lot of strain on the compressor, possibly to the point of compressor damage. Most compressors have some type of internal pressure relief device, which could open. But those devices are for short term duration. Hours of operation with the relief valve open can eventually damage the compressor. Equipment with high pressure limits will shut the condenser section down…it may require a “reset” or the limit may close automatically.
July 2, 2009 at 5:31 pm
thanks for your help. ill get a good grade on my midterm.
July 3, 2009 at 6:57 am
..I’ll send you an invoice for services rendered…
July 2, 2009 at 5:31 pm
What is the problem if you are on a service call for a heat pump system and the compressor is extremely hot and the suction line is also hot ?
July 3, 2009 at 7:04 am
..need more information to answer the question…is the system/compressor running? are you referring to the constant/true suction line between the reversing valve and compressor or the vapor line between the condenser and air handler? what are the system pressures? heat or cool cycle?
July 3, 2009 at 7:50 am
In reference to my previous question, my assumption is that the system is running in the cooling mode and the suction line is referring to the true suction line
July 3, 2009 at 9:19 am
..in that case, the reversing valve stuck mid-position/leaking, by-passing hot gas to the suction line, would be a good guess…
July 3, 2009 at 11:06 am
thank you for your help sir, it is truly appreciated. ill send you a check in the mail.