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Tech Challenge January 2021 – Answer

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A beer cooler utilizing R-134a with a TXV metering device with receiver, has a customer complaint of “warm product.” The symptoms confirm warm beer and the condensing unit is cycling frequently on the LPC (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.  193 deg. F
Condensing Press./Temp.  108 psig / 93 deg. F.
Condensing Outlet  78 deg. F.
Condenser Sub cooling  17 deg. F.
Condenser Split  18 deg. F.
Entering Feed Device Temp.  41 deg. F.
Evaporator Press./Temp.  3 psig / -7 deg. F.
Evaporator Outlet Temp.  37 deg. F.
Evaporator Superheat  30 deg. F.
Evaporator Split  37 deg. F.
Compressor Inlet Temp.  68 deg. F.
Total S. H.  61 deg. F.
Ambient Temp.  75 deg. F.
Room/Box Temp.  52 deg. F
Compressor Volts  240 V.
Compressor Amp. Draw LOW

ANSWER: The possible problem appears to be a partially restricted liquid line. This is verified by the entering feed device temperature of 41° F. being well below ambient temperature 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 temperatures and low refrigerant flow. A visual inspection of the liquid line, is likely to find a cold to the touch and possibly frosty filter drier.

Posted In: ACCA Now, Tech Challenge

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