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July 2015 Tech Challenge – Answer

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A freezer utilizing R-22 with a TXV metering device (and receiver) has a customer complaint of “warm case.” The symptoms at the store confirm that the case which normally operates at 0 degrees is at 32 degrees, and the condensing unit is running continuously. What are the possible causes (there is only one problem intended) with the following measured conditions on this field service check sheet?

Field Service Check Sheet

Compressor Discharge Temp. 238 deg. F.
Condensing Press./Temp. 168 psig / 90 deg. F.
Condensing Outlet Temp. 87 deg. F.
Condenser Sub cooling 3 deg. F.
Condenser Split 5 deg. F.
Entering Feed Device Temp. 86 deg. F.
Evaporator Press./Temp. 35 psig / 12 deg. F.
Evaporator Outlet Temp. 32 deg. F.
Evaporator Superheat 20 deg. F.
Compressor Inlet Temp. 54 deg. F.
Total S. H. 42 Deg. F.
Ambient Temp. 85 deg. F.
Room/Box Temp. 32 deg. F
Compressor Volts 240 V.
Compressor Amp. Draw Low

And the answer is…

The possible cause centers on an inefficient compressor. The head pressure is lower, and the suction pressure is higher than normal. This combined with a very high discharge temperature, is caused by the recompression of gases. The TXV is wide open, but there is very low refrigerant flow, which causes maximum subcooling and high superheat. The amps are low because the compressor isn’t working.

Posted In: ACCA Now, Tech Challenge

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