Tech Challenge – January 2014
A cooler utilizing R-134a with a TXV metering device (and receiver) has a customer complaint of “warm product.” The symptoms confirm warm product and the condensing unit appears to be running 100% of the time, with the low pressure control not being satisfied. 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.||180 deg. F.|
|Condensing Press./Temp.||105 psig / 90 deg. F.|
|Condensing Outlet Temp.||78 deg. F.|
|Condenser Sub cooling||12 deg. F.|
|Condenser Split||15 deg. F.|
|Entering Feed Device Temp.||42 deg. F.|
|Evaporator Press./Temp.||5 psig / -3 deg. F.|
|Evaporator Outlet Temp.||37 deg. F.|
|Evaporator Superheat||40 deg. F.|
|Compressor Inlet Temp.||68 deg. F.|
|Total S. H.||71 Deg. F.|
|Ambient Temp.||75 deg. F.|
|Room/Box Temp.||52 deg. F.|
|Compressor Volts||240 V.|
|Compressor Amp. Draw||Low|
Share this challenge with your technicians to find out if they can figure out the problem. You can also share your thoughts here by posting them in the comments section below. Check back after March 1, 2014, for the correct solution.
And the answer is…
The problem is a restricted liquid line. This is verified by the entering feed device temperature of 42° 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 temperatures and low refrigerant flow.
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