When servicing a refrigeration system, it is important to accurately determine the true cause of the failure. Misdiagnosing the problem can often create additional system issues for you and the customer.
Consider this example: You are called out to repair a self-contained cooler that is not cooling properly. You attach your low-side gauge — and only your low-side gauge — to the system and discover the suction pressure is lower than normal. You decide the issue is a loss of refrigerant and begin to add refrigerant back into the system in order to get the suction pressure up to a level that you believe is acceptable. You and the customer decide not to look for the leak at this point.
The next day, you get a call from the customer that the system is still not working. You go back out to the job and discover the compressor has failed. You blame the failure on age and maybe tell the customer that the loss of refrigerant caused the compressor to fail. The next day, you are back out to change the compressor, and as you are recovering the refrigerant, you discover that there is much more in the system than the data plate lists. You replace the compressor, weigh in the charge, and the system is back to running with a low suction pressure again. You eventually discover the capillary tube is restricted and needs to be replaced.
This scenario could have been avoided if you had also measured the high-side pressure during your initial inspection. At that point, you would probably have seen that as you were adding refrigerant to the system to get the suction pressure back up, the high-side pressure was getting higher and higher, and you would not have allowed the system to continue to operate. You would most likely have identified the capillary tube restriction before the compressor failed.
To accurately troubleshoot a mechanical issue with a refrigeration system, you should be looking at the whole picture. This means, at a minimum, examining both the low- and high-side pressures, as well as examining the condition of the evaporator and condenser. Depending on the system, you should also measure the temperature of the refrigerant leaving the evaporator and calculate its superheat value, as well as measure the temperature of the refrigerant leaving the condenser and calculate its subcooling value. Looking at all of these points will allow you to get a clear picture of how the system is running and why it is not cooling properly.
Don’t be a one-gauge technician. Looking at the suction alone is problematic, and looking only at the discharge pressure is problematic. You need to examine the system as a whole, not just sections of it. It is definitely a process that cannot be rushed; it takes time to do it right. As service professionals, we need to properly diagnose the cause of system issues and not misdiagnose the failure, or even worse, create additional problems.
Publication date: 2/4/2019