RSS

Category Archives: TROUBLESHOOTING HEAT PUMPS

Troubleshooting TXV Systems

(The content of this post is intended for consideration by trained service personnel only)

This short video illustrates the symptoms of some of the problems associated with TXV systems…can you diagnosis the numbers?

You can see a more in depth explanation of TXV operation and illustrated failures in the “Troubleshooting Heat Pump Refrigerant Systems” and “Troubleshooting TXV’s” rental videos:

Troubleshooting Heat Pump Refrigerant Systems

Troubleshooting TXV’s

 

Tags: , , , , ,

Overcharged System

(The content of this post is intended for consideration by trained service personnel only)

I was called on this unit, found some electrical problems and noticed the compressor sounded not quite right. On checking the compressor amp draw, it was running right at RLA. I messed with it a while and finally connected the gauges and temp sensors. What you’re seeing are the system pressures, saturated temps and liquid line temp. The net result is 50 degrees subcooling.

You can see an explanation and demonstrations of all the common refrigerant system failures in the “Troubleshooting Heat Pump Refrigerant Systems” rental video.

Troubleshooting Heat Pump Refrigerant Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Diagnosing Low Voltage Failures

(The content of this post is intended for consideration by trained service personnel only)

The system is a split heat pump, with the air handler in the attic. The HO had reported nothing was running. On arrival I flipped the stat fan switch to “ON” and nothing happened. Neither indoor nor outdoor sections running, usually indicates a low voltage failure or loss of high voltage to the transformer. Since the transformer is usually located in the air handler, that’s where to start the troubleshooting process.

Once I accessed the electrics, the problem was quickly discovered…

Blown fuses all too frequently indicate a short somewhere in the control voltage system. Maybe conductor failure or component failure. While at the air handler I ran some resistance checks and found the resistance low in the “Y” circuit going to the condenser unit.

At the condenser, I accessed the stat wire connections…

This one turned out to be easy. The stat cable had been lying against a section of tubing for a long time. The long term contact between the two eventually led to the insulation wearing through and “grounding” the “Y” conductor to the copper, creating the short and blowing the control voltage fuse.

You can get a full explanation and illustrations of all the common electrical failures in the “Troubleshooting Heat Pump Electrical Systems” videos for rent:

Troubleshooting Heat Pump Electrical Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Liquid Line Restrictions

(The content of this post is intended for consideration by trained service personnel only)

I started the service call guessing the problem was low charge, due to a leak somewhere, which isn’t a bad guess. The system is in heat cycle and you can see the frosted distributor lines, which can be caused by low charge. But after adding a pound or so of refrigerant, the suction pressure didn’t come up significantly, so I figured the problem was something else…

After connecting a temp sensor to the liquid line, it was fairly obvious the subcooling was much higher than it should be, which would indicate a restriction in the liquid line somewhere.

After looking over the refrigerant tubing and not finding any temperature drops ahead of the orifice distributor head, I knew the restriction had to be there.

And after disassembling the distributor and accessing the orifice, I found a piece of “something” partially blocking the orifice bore opening.

You can see an explanation and demonstrations of all the common refrigerant system failures in the “Troubleshooting Heat Pump Refrigerant Systems” rental video.

Troubleshooting Heat Pump Refrigerant Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Learning To Troubleshoot…Maybe Not

(The content of this post is intended for consideration by trained service personnel only)

We all start out in the service business thinking we have to learn how to troubleshoot and hoping we will some day. And if we stay in the business long enough, we eventually do. But the fact of the matter is, we didn’t really learn to troubleshoot because the truth of the matter is, you can’t learn to troubleshoot. What we end up learning is how stuff works…

If we were to try to define troubleshooting, the definition could be something like:

Troubleshooting is the process of collecting and analyzing information, then drawing conclusions from the information about how a system is operating.

What we’re doing when we troubleshoot is simply comparing the actual operation of a system to the expected or intended operation of the system. When we see the actual operation is different from the intended operation, we do whatever is necessary to determine the cause for the unexpected behavior. Which usually amounts to making some kind of electrical, pressure or temperature measurements. And the only way we can do that is by knowing what the expected or intended behavior is supposed to be, in the first place…knowing how stuff works.

If you can ever learn what heat pumps and furnaces are supposed to do, and what it takes to make them do it (learn how stuff works), troubleshooting becomes an instinctive, or maybe subconscious, response to an unexpected behavior. There’s nothing to learn about troubleshooting.

Let me illustrate what I’m saying…Say we go on a heat pump service call to investigate a “no cooling” complaint. In order for the system to initiate a “call for cool”, what’s supposed to happen?

We know a switch (or switches) inside the thermostat has to close and send 24 volts to the contactor coil, the reversing valve solenoid (with most equipment brands) and the blower motor control. Then the contactor coil is supposed to “pull-in”, completing the high voltage circuits to the compressor and condenser fan motors. The blower motor control also closes a switch, completing the high voltage circuit to the blower motor and the reversing valve solenoid causes the pilot valve to shift, which in turn results in the main valve shifting. If all that takes place as designed, the compressor motor, condenser fan motor and blower motor start, and the reversing valve directs the refrigerant flow in the right direction.

At that point, the intended/expected operation amounts to the correct or design volume of air being moved by the condenser fan and blower wheel, the compressor pumping the design volume of refrigerant, the reversing valve channeling the refrigerant flow in the right direction and the TXV maintaining the correct amount of liquid entering the evaporator coil. And of course, we confirm whether or not all that has happened simply through visual observations, system pressures and temperature measurements.

If our visual observations tell us the condenser didn’t start, we would logically begin troubleshooting for some electrical issue. The first thing we would do is check whether or not the contactor has pulled in. If not, the troubleshooting process begins with an analysis of the low voltage circuits. We would check for voltage on the “hot” side of the contactor coil. If the meter reads zero, we start “backing up” towards the low voltage source, which is the thermostat in this case, looking for the open circuit.

If the contactor has pulled in, then the high voltage circuits are suspect. We would begin by checking for high voltage at the contactor L1-L2 connections for power coming into the condenser unit. If there was no voltage there, you’d begin “backing up” towards the high voltage source, which is a breaker somewhere in the panel box.

In either case, it is our knowledge and understanding of what is supposed to take place, and our ability to reason through information, that tells us where to check for voltages.

If on the other hand, everything appears to be running, you initially begin the troubleshooting process with the assumption there is some problem with the refrigerant system. We confirm that by measuring system pressures, superheat and subcooling.

The expected behavior of an R-22 system would generate a suction pressure in the 70-80 psi range and a superheat in the 10-15 degree range. If you measured 50 psi and 30 degrees, you’d know something is wrong. If you understand what has to take place in order for the numbers to be 70-80 psi and 10-15 degrees, you would know there is not enough refrigerant entering the evaporator coil. And you would also know that has to be due to an undercharged system, a faulty TXV or liquid line restriction. At that point you have to evaluate the head pressure and subcooling to decide which of those possibilities is the problem. If the head pressure and subcooling are low, the problem is low charge. If the head pressure is in the normal range and the subcooling on the highish side, you know the problem is one of the other possibilities.

But to emphasize my point again, we didn’t learn to troubleshoot the problems…our knowledge of what the heat pump is supposed to do, instinctively led us to follow a logical procedure of observations and measurements, which resulted in a conclusion explaining the unexpected behavior of the heat pump.

The videos I’ve made available take a practical approach teaching “how stuff works”. If you already have some training in the fundamentals, the video content will help you apply your knowledge to real world situations in the field.

(The content of this post is intended for consideration by trained service personnel only)

 

Tags:

TROUBLESHOOTING HEAT PUMP SYSTEMS…INDOOR / OUTDOOR TEMPS VS SUPERHEAT W/ FIXED ORIFICE SYSTEMS

(The content of this post is intended for consideration by trained service personnel only)

..If you look at a superheat charging chart for a fixed orifice system, you quickly see the required superheat varies with outdoor and indoor conditions. As the outdoor temperatures vary, so does the required superheat…pretty much the same relationship for indoor temperatures. Why? The net force pushing liquid through the metering device is the difference in the head and suction pressures, more or less.

The point being, if the outdoor temperature is 75F you don’t won’t want a “beer can cold” suction line…because by the time the afternoon temperature hits mid-90’s, the increased head pressure will have increased the “net force” pushing the liquid through the orifice, and the system will be overcharged, resulting in a lower than desired superheat.

Likewise, if the indoor temps are “high”, superheats will be high. Most charging charts use indoor wetbulb as the control variable, since wetbulb temps include the humidity factor. As indoor wetbulb goes down, the superheat will decrease, everything else being equal. The following clip demonstrates variations in superheat with outdoor conditions.

You can see an explanation and demonstrations of all the common refrigerant system failures in the “Troubleshooting Heat Pump Refrigerant Systems” rental video.

Troubleshooting Heat Pump Refrigerant Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Tags: , ,

TROUBLESHOOTING HEAT PUMP SYSTEMS…OPEN CONTROL VOLTAGE CIRCUITS

(The content of this post is intended for consideration by trained service personnel only)

One of the more frustrating and difficult situations with heat pump diagnostics is open circuits in the control wiring. There is a logical process to follow when attempting to locate the failure…

You can get a full explanation and illustrations of all the common electrical failures in the “Troubleshooting Heat Pump Electrical Systems” videos for rent:

Troubleshooting Heat Pump Electrical Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Tags: , , ,

TROUBLESHOOTING HEAT PUMPS…DIAGNOSING PSC MOTORS

(The content of this post is intended for consideration by trained service personnel only)

A common failure with residential equipment condenser and blower motors is not actually the motor, but the run capacitor. Probably the majority of the time, the capacitors fail “open”…the motor can’t develop the necessary torque to actually begin rotation. So, it justs sits in a “stalled” condition, pulling above normal amps…the video gives some thoughts on the subject.

You can get a full explanation and illustrations of all the common electrical failures in the “Troubleshooting Heat Pump Electrical Systems” videos for rent:

Troubleshooting Heat Pump Electrical Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Tags:

TROUBLESHOOTING HEAT PUMP SYSTEMS / RECOGNIZING LOW AIRFLOW

(The content of this post is intended for consideration by trained service personnel only)

One of the more common problems found in service work is low airflow across the indoor coil. This situation can be due to coil restriction, inadequate/damaged ductwork or dirty filters to name a few. Much has been written in regards to airflow and it’s critical role for proper heat pump operation and performance. The design value for indoor airflow with A/C’s and heat pumps has, to the best of my knowledge, always been 350-450 CFM per ton. Values less than 350 generally create operational problems like coil frosting in the cool cycle or high head pressure in the heat cycle. Values greater than 450, though the lesser of two evils, would produce situations better described as performance problems…poor moisture removal in the cool cycle, or low discharge temperatures in the heat cycle. But, with typical residential systems, excessive airflow is rarely a problem, simply because residential duct systems are rarely oversized. So, the usual situation becomes one of recognizing and correcting low system airflow.

All residential equipment, be it heat pump air handlers, gas furnaces or packaged units, is limited in its capacity to move air and the limiting factor is system external static pressure. External static pressure is for all practical purposes, a measurement of the resistance encountered by the air as it moves through the duct/air distribution system. The standard for maximum ESP is about 0.5 inWC, and residential duct systems have to be designed and sized, to meet this capability of the blower. Otherwise, the ESP may exceed 0.5 and the airflow per ton will be less than 350 CFM…

With no practical understanding of system operation, determining airflow volume would require taking some kind of measurements and doing some calculations that eventually provide a CFM value. Or, if a specific value of airflow is required, so will be the measurements and calculations. But for me, most of the time, the issue comes down to either having enough airflow, or not. And by “enough” I simply mean, the system will run 24 hours without frosting the indoor coil in the cool cycle, or producing excessive head pressures in the heat cycle. Now, if you’re attempting to evaluate overall system performance and efficiency, which depends to a great extent on airflow, “enough” probably isn’t adequate. But keep in mind, service calls are usually situations where the homeowner was content with the system performance yesterday, but not today. So, I always start with the assumption the airflow has at some point in time, been satisfactory, adequate or “good enough”…and most of the systems I find fall into this category. All I need to do is return the system airflow volume back to or near, whatever it was on Day 1, regardless what that actual value is. And that usually amounts to changing a filter, or cleaning the coil.

Airflow calculations aren’t necessary to decide there isn’t enough. If, in the cool cycle, the suction pressure is low and the superheat is low for fixed orifice systems, or normal for TXV systems, the airflow is low. If, in the heat cycle, the head pressure is high, the cause is either overcharge or low airflow, or both…sometimes, techs will overcharge a fixed orifice system in the cool cycle to correct low suction pressure resulting from a dirty indoor coil. But you can ask a few questions to determine if that’s the case. Common sense dictates indoor coils will restrict over time, due to a variety of possible reasons. So when you see symptoms of low airflow, that’s the first thing to suspect. Occasionally you get lucky and find a dirty filter, but more often than not, the coil is the culprit.

You can see a more in depth explanation of refrigerant system operation with low evaporator air and illustrated failures in the “Troubleshooting Heat Pump Refrigerant Systems” rental video:

Troubleshooting Heat Pump Refrigerant Systems

(The content of this post is intended for consideration by trained service personnel only)

 
1 Comment

Posted by on March 28, 2008 in TROUBLESHOOTING HEAT PUMPS

 

Tags: , , ,

TROUBLESHOOTING HEAT PUMP SYSTEMS…RESTRICTED LIQUID LINE FILTERS

(The content of this post is intended for consideration by trained service personnel only)

Liquid line filters occasionally restrict for whatever reasons, resulting in a significant pressure drop across the filter. The restriction forces more than the normal amount of liquid refrigerant to remain in the condenser coil, which will increase the subcooling value. Head pressure will usually drop a little or remain near normal, while suction pressure will be low and superheat high, due to the evaporator coil being underfed. Of course, where pressure measurements are taken relative to the filter location will determine “head” pressure readings. If the filter is located upstream of the pressure port, the reading would reflect the pressure drop across the restriction and be low. One of the best methods for recognizing a restricted filter is a temperature drop through the filter. The restriction and pressure drop most often creates “flash gas” which generates some refrigeration effect, and causes the filter to cool. A noticeable difference in temperature between the inlet and outlet of the filter is a definite symptom of some restriction. The following clip from the heat pump refrigerant video provides a good visual.

Troubleshooting Heat Pump Refrigerant Systems

(The content of this post is intended for consideration by trained service personnel only)

 

Tags: , , ,

 
Follow

Get every new post delivered to your Inbox.