Tech Challenge – November 2012
A beverage cooler utilizing R-134a with a TXV metering device (and receiver) has a customer complaint of “warm brew.” The symptoms at the convenience store confirm warm product and the condensing unit appears to be cycling on the low or high pressure control. What are the “possible causes” with the following measured conditions on this field service check sheet?
Field Service Check Sheet
|Compressor Discharge Temp.||180 deg. F.|
|Condensing Press./Temp.||205 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 January 2 for the correct solution.
And the Answer is…
The possible causes of warm beer center on a liquid line restriction. The temperature of the liquid entering the TXV is well below ambient tells us that some evaporation has taken place before it got to the TXV. If the liquid line and filter/drier are also cold, a partially restricted filter/drier is the culprit. The pressures and amps are low because the liquid line is a very small evaporator and it is not picking up heat. The system is not working very hard.
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