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Tech Challenge July 2019 – 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 that normally operates about 0 degrees is 34 degrees and the condensing unit is running continuously. What are the “possible causes” (note: there is only one problem intended) with the following measured conditions on this field service check sheet? 

Field Service Check Sheet

Compressor Discharge Temp.  240 deg. F
Condensing Press./Temp. 168 psig / 90 deg. F.
Condensing Outlet  87 deg. F.
Condenser Sub cooling  3 deg. F.
Condenser Split  5 deg. F.
Entering Feed Device Temp.  86 deg. F.
Evaporator Press./Temp.  39 psig / 16 deg. F.
Evaporator Outlet Temp.  38 deg. F.
Evaporator Superheat  22 deg. F.
Compressor Inlet Temp.  54 deg. F.
Total S. H.  38 deg. F.
Ambient Temp.  85 deg. F.
Room/Box Temp.  34 deg. F
Compressor Volts  240 V.
Compressor Amp. Draw  Low

ANSWER: The possible cause appears to be an inefficient compressor. The head pressure is lower and the suction pressure is higher than normal with a very high discharge temperature caused by the recompression of gases. The TXV is wide open, but there is very low refrigerant flow causing maximum subcooling (to with-in 2 deg. of ambient) and high superheat. The amps are low because the compressor isn’t working. A compressor efficiency check per manufacturers specifications needs to be accomplished. 

Posted In: Tech Challenge

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