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January 2017 Tech Challenge – Answer

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A Coca Cola cooler utilizing R-134a with a TXV metering device with receiver, has a customer complaint of “warm pop.” The symptoms confirm warm product and the condensing unit is cycling frequently on the low pressure control. With only one problem intended, what are the “possible causes” with the following measured conditions on this field service check sheet??

Field Service Check Sheet

Compressor Discharge Temp. 185 deg. F.
Condensing Press./Temp. 106 psig / 91 deg. F.
Condensing Outlet Temp. 78 deg. F.
Condenser Sub cooling 13 deg. F.
Condenser Split 16 deg. F.
Entering Feed Device Temp. 43 deg. F.
Evaporator Press./Temp. 5 psig / -4 deg. F.
Evaporator Outlet Temp. 38 deg. F.
Evaporator Superheat 42 deg. F.
Compressor Inlet Temp. 68 deg. F.
Total S. H. 72 deg. F.
Ambient Temp. 75 deg. F.
Room/Box Temp. 52 deg. F
Compressor Volts 240 V.
Compressor Amp. Draw  Low

Answer: The problem appears to be a restricted liquid line. This is verified by the entering feed device temperature of 43° F. (below ambient) caused by a liquid line partial restriction causing flash off (evaporation). The low side is starved giving high superheats and the high side follows the low side because the system is not picking up much heat. The discharge temperature is high because of the high superheated inlet temperature and low refrigerant flow.

Posted In: ACCA Now, Tech Challenge

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