May 2014 Tech Challenge Answer


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A Roof top system utilizing R-22 with a fixed orifice-metering device has a customer complaint of “no cooling.” The symptoms at the customer’s office confirm that the thermostat is not satisfied and the compressor, condenser fan, and blower are running continuously. What are the “possible causes” using the following measured conditions on this field service check sheet?

Field Service Check Sheet

Compressor Discharge Temp. 210 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. 86 deg. F.
Evaporator Press./Temp. 82 psig / 49 deg. F.
Evaporator Outlet Temp. 65 deg. F.
Evaporator Superheat 16 deg. F.
Compressor Inlet Temp. 78 deg. F.
Total S. H. 27 Deg. F.
Ambient Temp. 85 deg. F.
Room/Box Temp. 80 deg. F.
Compressor Volts 240 V.
Compressor Amp. Draw Low

And the answer is…
The possible cause centers on that of an inefficient compressor. The discharge pressure is lower and the suction pressure is higher than normal with low refrigerant flow as evidenced by the high superheats, low splits, and low amps. The high discharge temperature is likely caused by recompression and very low refrigerant/high superheated vapor coming back to the compressor.


Posted In: ACCA Now, Tech Challenge

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