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Tech Challenge – September 2013

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A residential split AC system utilizing R-22 has a customer complaint of “no cooling.” The symptoms at the customer’s home confirm that the thermostat is not satisfied and the condensing unit and blower are running continuously. The system has a fixed orifice. What are the “possible causes” with the following measured conditions on this field service check sheet?

Field Service Check Sheet

Compressor Discharge Temp. 230 deg. F.
Condensing Press./Temp. 182 psig / 95 deg. F.
Condensing Outlet Temp. 87 deg. F.
Condenser Sub cooling 8 deg. F.
Condenser Split 10 deg. F.
Entering Feed Device Temp. 87 deg. F.
Evaporator Press./Temp. 86 psig / 52 deg. F.
Evaporator Outlet Temp. 65 deg. F.
Evaporator Superheat 13 deg. F.
Compressor Inlet Temp. 76 deg. F.
Total S. H. 24 Deg. F.
Ambient Temp. 85 deg. F.
Room/Box Temp. 81 deg. F.
Compressor Volts 240 V.
Compressor Amp. Draw Low

And the answer is…

The possible causes point to an inefficient compressor. The first sign is a very high discharge temperature that is likely caused by recompression and low refrigerant flow through the system. The pressures between the high side and the low side have moved closer together and the splits are low along with low amps telling us that the system is not working. The high evaporator temp/press is probably caused by an inefficient compressor that is not pulling refrigerant from the evaporator and the evaporator is not picking up much heat. The next step, perform a compressor efficiency test.

Posted In: ACCA Now, Tech Challenge

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