TROUBLESHOOTING HEAT PUMP SYSTEMS…R-22 VS R-410A
Unless you’ve been living under a rock for the past several years, you know R-22 is on the way out and R-410A appears to be the manufacturer’s weapon of choice for heat pump and comfort cooling equipment. If you’ve already encountered a 410A system and had a less than pleasant experience, possibly attempting to correct or understand what appeared to be abnormally high system pressures, your confusion may be with a misunderstanding of mechanical refrigeration, rather than the refrigerant.
Mechanical refrigeration is all about heat transfer and temperatures, especially boiling and condensing point temperatures. The whole point of a refrigeration system is that of creating a heat sink or low heat energy level, causing heat to transfer from a higher energy level. For comfort cooling applications, the indoor coil operates at a temperature lower than that of the indoor air temperature, and I’ll say in the 40ish degree range. When the system is in operation, the indoor air is pulled through the coil, where some of it’s heat is transferred to the coil. That heat is then carried to the outdoor coil, where it is transferred to the outdoor air. When heat pumps are operating in the heat cycle, the outdoor coil has a temperature less than the outdoor air temperature. Then the heat in the outdoor air transfers to the refrigerant in the outdoor coil, is carried to the indoor coil, where it is transferred to the indoor air. So, the dynamics of a mechanical refrigeration system simply control the refrigerant temperatures within the indoor and outdoor coils, maintaining a continuous process of heat transfer, in whatever direction is needed.
I don’t claim or even pretend to know, the engineering details necessary for the design of refrigeration systems. But I have a reasonably good idea of how they’re supposed to operate, relative to system pressures, subcooling and superheat, and particularly with comfort cooling and heat pump applications. And so long as I know what refrigerant the system uses, and have a way to convert pressures to saturated temperatures, I’m comfortable with the system. We’re all probably guilty of becoming familiar with system pressure measurements, and forgetting what we’re actually measuring, which is the saturated refrigerant temperatures in the evaporator and condenser coils. Once we see what those numbers are, we then measure the suction line and liquid line temperatures so superheat and subcooling values can be calculated. With the system pressures / saturated temperatures, superheat and subcooling values, we can make an intelligent decision about the operation of the system.
An R-22 system operating in the cool cycle on a hot summer day will usually run a suction, or low side pressure, of 75 psi or so. And the superheat could range from 5 to 15 degrees depending on the type metering device, equipment brand and outdoor temperature. An R-410A system would be running around 120 psi low side, but would have a similar superheat range, again depending on the metering device, brand and outdoor temperature. The difference in pressures is due simply to the difference in saturated temperature / pressure characteristics of the two refrigerants. So long as your gauges have a “temperature conversion scale” for the type refrigerant you’re working with, and you know what the evaporator temperature is supposed to be, you can analyze the system for proper charge and operation, whether or not the pressures are “familiar”.
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June 9, 2008 at 5:03 pm
Always and forever temps will remain the same (drops super heat subcool) pressures’ will not.
July 6, 2008 at 11:30 am
Sun. 7-6-08 I am a homeowner and just installed a 13 seer case coil on a 90%, 90,000 btu furnace, all Goodman brand. Now I am trying to decide to go with 410a or R-22. Wayne I have 2 questions.#1.)Did I have to buy a special 410a case coil or is the same Goodman case coil used for both refrigerants. #2.) In your professional opinion which one gets and stays the coldest? Thank you, Bob Mullins ph.#734-444-6210
July 6, 2008 at 1:26 pm
1) ..at least some equipment mfg’s use the same coil for either refrigerant…only the refrigerant metering device is different, which is a crucial engineering point. In theory, the metering device can be changed to accommodate 410A, but not all mfg’s will support or even accept that retrofit procedure as a viable option…you are likely overlooking one aspect of R-410A systems…they require a type oil not normally found in R-22 systems. Only trace amounts of “R-22 oil” are allowable in 410A systems…you probably have an outdoor unit running on 22 and full of “22 oil”…in addition, there is the question of whether or not the outdoor unit would perform properly with the 410A refrigerant, which I can’t begin to answer…so retrofitting to 410A is not a simple matter of “take out the old, put in the new” …
2)..regardless of refrigerant type, A/C systems remain one application of mechanical refrigeration which is determined by the “indoor” coil internal operating temperature, and that design temperature range hasn’t changed, to my knowledge. I hear occasional comments that systems with the new stuff don’t get as cold ??? and I don’t have any scientific data to support or dispute the claims, but personally, I think the argument is a crock. There may be situations where the capacity of a 410A replacement system is less than the original 22 system, which would explain some apparent loss in cooling ability. I replaced my 22 old system with 410A equipment…it seems to cool better…
July 15, 2008 at 4:15 pm
Wayne,
I am in the process of replacing my old r22 system with a new 410a based system. I will be replacing both the external as well as the internal units. My question is whether the old copper tubing can sustain the pressure required by the new 410a refrigerant. I understand that it will unless there are soldered joints that might give way due to the increased pressure required by the 410a. I don’t know if there are any joints in the tubing. Is my concern valid?
July 15, 2008 at 8:01 pm
..if you decide to use the existing copper and leaks develop, it won’t be the result of the new refrigerant.
Your question led me to do a little research…the burst strength of refrigeration grade copper tubing is 3000+ psi…R-410A systems don’t develop pressures geometrically greater than R-22. A new 13-14 SEER system operating per design conditions will run maybe 350-400 psi on the high side. Some of the old 22 systems with dirty heat exchange coils will run that high. I’ve observed over the years, copper in refrigeration applications doesn’t generally deteriorate over time, unlike water plumbing which can “eat through” sometimes…seems like water and air are far more detrimental to copper than refrigerants and refrigerant oils.
So far as joints, a good silver solder brazed connection has more strength than the copper, and “new copper” will be soldered at the equipments’ factory stubs, so you’ll still have “soldered joints”.
Some A/C guys like to change the copper when replacing equipment as a matter of standard practice. The more valid explanation for replacing copper is to eliminate any questionable or potential contamination in the old tubing, or change sizes to better match the equipment requirements. But there are flushing agents available which will pretty much take care of the contaminants. And obviously, it’s not always feasible to replace the copper…you got to be able to access it freely.
July 16, 2008 at 9:53 am
Thanks Wayne. Your advice helped a lot.
September 5, 2008 at 11:43 pm
I AM ATTENDING A VOCATIONAL SCHOOL FOR HVACR THIS IS MY FIRST TIME ON YOUR WEBSITE, YOUR INFORMATION IS VERY HELPFUL AND YOU HAVE MADE IT VERY CLEAR YOU KNOW WHAT YOUR TALKING ABOUT I WILL DEFINENTLY PASS THE WORD TO MY CLASSMATES
September 10, 2008 at 5:03 pm
A goodman R410a 16 SEER heat pump system (SSZ16024 HP and AEPF303616 AH with TXV) was installed 2 months ago. The house feels humid. Suction pressure reads 135 and discharge reads 240. My rudimentary temp readings are ambient=86, inhouse=72, return air=72, supply air=60, liquid line @ condenser=92, suction line @ evaporator=69, indoor wet bulb=67. Sound close to right?
Thanks
John
September 10, 2008 at 8:02 pm
..your measured values calculate out to 20+ degrees superheat and a negative subcooling value. That along with the 240 head pressure would seem to indicate undercharge. 72 return and 60 supply gives a 12 degree “split”…I would think 15-20 is probably closer to normal…I’m not all that familiar with Goodman equipment/model numbers, but the H/P number looks like a 2 ton, and the air handler a 2-1/2 to 3 ton…What capacity is (was) the system supposed to be, what state are you in and how many square feet is the house?
September 11, 2008 at 9:01 pm
The HP is a 2 ton, The air handler is as you suspect a larger unit. The location is east/central PA. The unit handles 1100 sq ft. The reasoning for the inside unit was a desire for maximum heat production, not the most efficient AC.
Manual says for high superheat and low subcooling , add charge to get 7 plus or minus 2 degrees subcooling and then adjust TXV to set superheat to 7-9 F.
At installation, HP came with enough for 15 feet of line, we added .6 oz/ foot of line for 17 feet = 10.2 oz. Seems we neglected to add for the evaporator coil. Idea as to how much that would take?
Thanks for your help.
September 11, 2008 at 10:56 pm
..there’s nothing wrong with over sized air handlers, IMO. It was a common practice around here in the “early days” of heat pumps. The theory is the mis-match will improve humidity removal in the cooling season as a result of greater coil surface area. I’m not sure about increased heat, since the outdoor unit can only generate so much, regardless of indoor size…unless you’re referring to the auxiliary elements. I would suggest slowing the indoor blower speed to the lowest selection, if that hasn’t been done.
So far as additional charge, I’ve never been keen on weighing in, which is a purely personal thing, and don’t have a clue as to how much additional you need…the procedure you followed should have gotten you closer than it appears to have… just add refrigerant a few ounces at a time, while monitoring the subcooling. If the TXV requires adjustment for the 7-9, you’ll need to watch it also. The equipment I work with comes with non-adjustable TXV’s, so superheat is…whatever it is.
September 12, 2008 at 10:56 am
Thanks very much for the time.
Last question… with R410a, what pressure values would you expect for this 2 ton, Copeland scroll unit?
Best regards
John
September 12, 2008 at 5:27 pm
..refrigeration is about temperatures..refrigerants are about pressure. Indoor coils for comfort cooling run in the 40 F temp range and condensing temps probably in the 100-110 F. With decent indoor and outdoor temps, suction and head with 410A probably 115-140, 315-350 respectively.
March 24, 2009 at 5:33 am
I’m concerned if I over-rated a replacement Heat Pump in which I didn’t fully diagnose before replacing. The unit I replaced was a 3 ton, and I increased it to 3.5 ton. After discovering that the previous tech had reduced the line set sizes from 3/8 liquid to 5/16 and 7/8 suction to 3/4, I’m now lost in what this 3 bedroom, two floor house originally required ?
Not realizing, after hook-up to a R-410a, I contaminated the condensing unit. Should I roll-out the whole system or drain the condensing unit and replace the compressor…..as well as the other goodies ?
March 24, 2009 at 5:34 am
Please notify and let me know, I’ll be checking in. Thanks.
March 24, 2009 at 6:18 am
..you lost me with some of the details. You had a 3 ton split, R-22 system and replaced the condensing unit only, with a 3.5 ton 410A condenser unit? What’s the square footage of the home? How long is the line set?
March 26, 2009 at 1:25 am
Anyone know what the suction & liquid line pressure’s are to be on a 13 SEER R-410a heat pump ? Ambient 50deg. F Is it 130 suction & 418 liquid ?
March 26, 2009 at 10:22 am
..there should be some service literature with the unit to answer that question…
March 30, 2009 at 5:00 am
Well, the problem is in the air distributing ductwork. The existing plenum is 10″ x 20″, so you can see there’s a problem with this previous second floor upflow installation. It’s a two floor home with about 1500 square feet. Two return grilles first floor and second floor. Lineset is 25 feet. The Goodman unit required that if the condensing unit was lower then the evaporator, a loop of the suction piping must be higher then the evaporator…….doesn’t make sense, and no explanation to that determination either ?
After 8 hours of operation (5:00am), the customer would call saying there was a loud grinding noise coming from the outside unit. Either a floodback occured during defrost or the compressor starved for oil, which resulted in compressor failure. I’m going to have to eat it and start over.
The lineset has been replaced (7/8 & 3/8) and the Goodman unit was a restrictor (fixed) type. Calling around, I failed to see that 1200 cfm is not sufficient for 1500 cfm requirement (3.5T), so I have to drop it down back to 3 ton respectively. “ooooh, R-410a is a nightmare.”
March 30, 2009 at 5:07 am
I’m loosing track, what I’m looking for is the correct pressures for Suction and Liquid lines, when the ambient is say, 50deg. F. ? Should I go with sub-cooling procedures instead ? The Goodman unit has 181 ounces (11-5/16lb R-410a), I believe this is for 15 feet of lineset ? Start up pressures were 96-LP & 450-HP Ambient = 58deg. F.
March 30, 2009 at 7:37 am
The “loop” in the suction line is standard piping recommendations…prevents oil slugs returning to the compressor.
..I never did quite understand whether or not the indoor and outdoor unit were matched…did you replace the air-handler with a 3.5 ton 410A rated unit to match the outdoor unit, or did you replace only the outdoor unit?
Airflow is always critical…admittedly, 350 cfm per ton might work, but it is minimum, and will result in high head pressures in the heat cycle and low suction pressures in cool cycle.
I can’t say 100% what the system pressures would be for the Goodman equipment in the heat cycle. Based on some other brands service literature, the suction is a little low and head a little high for the outdoor ambient you gave. In the heat cycle, indoor temperature will affect the head pressure. Again, the equipment service literature should include a chart showing pressures versus indoor and outdoor temperatures.
Most equipment mfgs don’t provide a superheat or subcooling method for charging in the heat cycle…it’s nature of the beast. But 95 LP and 400 HP would be reasonably decent for 50 F ambient…but all that is based on matched equipment with the correct airflow.
March 31, 2009 at 6:34 am
Thanks Wayne,
Yeah, I know about the beast…..no SC or SH chart for heating, I would get this mess in the winter ? This is also why I’m rolling it out and putting in a 3 Ton. Air Flow was definitely a factor, and I’m sure after 8 hours of operation, that’s what killed the comp. I just realize, that this refrigerant is a slow boiler, if the pressures aren’t high enough…..that’s what I couldn’t put my finger on. I’ll keep your advice for future reference.
Thanks again.
March 31, 2009 at 6:44 am
Oh yeah, back to the trap question: The condensing unit being lower, then the evaporator doesn’t require a trap, only if the opposite happens…..like in Supermarket Open freezers etc. I could see if there was a trap, it would crowd the evaporator of it’s performance ? I don’t know, let me know ?
March 31, 2009 at 8:27 am
I’ve been installing 410A replacement systems since 2002, with and without traps, 3/4″, 7/8″, 3/8″ and 5/16″ tubing…whatever is there, but haven’t had any compressors fail after 8 hours. The failures I’ve experienced with 410A systemsare no worse than 22 equipment. Your first post mentioned swapping a 3.5 for a 3.0 and contaminating something with a 410A…You never answered the question of whether or not the equipment you’re working with is a matched system…
I assume you know 410A equipment uses a synthetic oil and 22 systems use something else…and the synthetic won’t mix with the something else. The equipment mfg’s started out saying 410A systems could not be contaminated with any amount of mineral oil, meaning linesets had to be new (clean) with 410A equipment. They have since, backed off that stance to some degree, I assume, realizing some linesets can’t realistically be replaced. They recommend purging the linesets with nitrogen to remove any excess mineral oil. I’ve started using a flushing agent to improve the removal of old oil.
I haven’t seen or even heard first hand, of a 410A system contaminated with a lot of mineral oil, but can see where it might cause an 8 hour failure…
The real booger-boo with the synthetic oils is their “hygroscopic” tendencies: they absorb moisture more readily than mineral oil, and the moisture can’t be removed with a vacuum pump. That fact still wouldn’t account for an 8 hour compressor failure, as it will produce long term effects.
I have no idea why the compressor failed after 8 hours, but doubt it was the result of tubing diameter, traps, airflow or any particular characteristic of 410A refrigerant…it could have simply been a bad compressor.
April 5, 2009 at 7:25 am
Yeah, one tech told me linesets wasn’t important either, but another told me that incorrect air flow would cause high pressures which would blow out the oil in the compressor during defrost and thus tear it up internally. Now, looking over the years of replacements on this house, I’m wondering if when it was built, was it a 2.5 Ton Heat Pump ? Seeing the second replacement was a Trane 3 T., with the lineset in the wall being 5/16 & 3/4; in which they adapted to 3/8 & 7/8, obviously, this was an upgrade and probably an increase in rating also.
The second tech said that the coldest period of the day is when ? I replied, around 5 o’clock in the morning, and that’s when the noise was errupting from the compressor in which the customer would call. Driving to the site in 40 minutes, I’d find it was in defrost mode of operation, when she switched to emergency heat as I requested. I restarted the heat pump cycle, finished defrost, it would resume back to normal heating until the next morning, around 3 to 5 o’clock in the morning, when it would do it again. After racking my brain for about three times of this, the compressor finally failed……both suction and high side pressures equalized at 180psi while in operation.
Now, rolling it out and replacing with a Ducane 3 T., I nearly fainted when I saw the air handler cover saying it was a 42,000 btuh evaporator ! I called back to the distributor, and knowing I wanted a 3 T, which is what the condensing unit is, he exclaimed,….. “Jeff, you’re doing good, keep going; you’ll be Ok.” I’m thinking of going to my doctor and get some chill pills cause this 410a unit is going to send me to the nut ward !
I wasn’t satisfied so I called tech support and Frank said, it was normal to over-rate the air handler to the condensing unit, then he went on about the lineset being looped over, higher then the evaporator and about traps. I asked about High & Low Side pressures, and he said, that’s already been taken care of and are printed on the inside of the condensing unit cover.
I purged with nitrogen, dehydrated down to 5u….holding at 500u for 10minutes. I did this twice so as to be able to re-install the cores back in the service valves.
With an ambient of 63 F., my pressures are suppose to be 355 HP & 109 LP. My guages read 305 HP & 70 LP, in which I’m seeing is undercharged. Sub Cooling: Liq.Line Temp. = 93.6 F, in which climbs to 94.8 and then returns back to 93.6 F. (Restrictor System). Switching to the pressure chart, I get 97 F. Subtract and I get 3.40 degree, which is definitely too low. I told her keep it in Em.Heat, until I make sure we don’t blow the oil out of the compressor like we did before. It’s probably Ok, but all this work commences at 6 o’clock in the evening, which is the only time I can get in to complete the replacement, so you can see why I’m being over cautious with this animal.
Oh well, with a learning curve ball like this one, I struck out big time, but I promise, it won’t happen again….that’s for sure.
May 17, 2009 at 9:24 pm
Hi wayn,
i bought 12btu mini split a/c precharged after i install it and open the high pressure port i found a leak i guess some of the freon gone , how to charge it do i need a vacuum pump can i use a gage and 25lb r410a
May 19, 2009 at 6:57 am
..your best approach in that situation would be to weigh in the charge, in which case you’d need a recovery machine, recovery drum, vacuum pump, manifold/gauges and scales…and knowledge of how to use it all. You’d probably be better off calling a service company…
May 19, 2009 at 9:50 pm
do i need a recovery machine and drum, can not i open the valve and let the freon goes, or if iam a bit low cann’t i use just manifold/gauges and r-410a freon and add just a bit , would this damage my compressor , do i must use a vacuum pump to add freon, thanks alot i paid $500 for the whole unit precharge i guess will cost me more just to call the company and add freon
thanka again
May 19, 2009 at 10:27 pm
..you could add some refrigerant if you knew what you were doing, with the gauges and jug of 410A…which is why I suggested calling a service company. I don’t mean to be rude or blunt, but without some knowledge and expertise, the more you mess with it, the worse the situation may get…