Tech Challenge – July 2013
A split medium temperature cooler, normally operating at 34° F. utilizing R-134a with a fixed orifice metering device has a customer complaint of “warm product.” The symptoms confirm that the pressure control is not satisfied and the condensing unit and evaporator blower are running continuously. What are the “possible causes” (there is only one problem intended) with the following measured conditions on this field service check sheet?
Field Service Check Sheet
|Compressor Discharge Temp.||210 deg. F.|
|Condensing Press./Temp.||171 psig / 120 deg. F.|
|Condensing Outlet Temp.||100 deg. F.|
|Condenser Sub cooling||20 deg. F.|
|Condenser Split||40 deg. F.|
|Entering Feed Device Temp.||90 deg. F.|
|Evaporator Press./Temp.||22 psig / 25 deg. F.|
|Evaporator Outlet Temp.||30 deg. F.|
|Evaporator Superheat||5 deg. F.|
|Compressor Inlet Temp.||55 deg. F.|
|Total S. H.||30 Deg. F.|
|Ambient Temp.||80 deg. F.|
|Room/Box Temp.||42 deg. F.|
|Compressor Volts||240 V.|
|Compressor Amp. Draw||High|
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 September 1 for the correct solution.
And the answer is…
The Possible Cause for these conditions center on a system overcharge. The overcharge would cause high head pressure/temperature and split because the condenser is largely filled with liquid refrigerant reducing its effective size (area of heat transmission). The low side is following the high side to higher pressures/temperatures thus preventing adequate cooling. The high discharge temperature is caused by the high superheat. The unit may also be cycling on the high head pressure control or compressor overload if the outdoor ambient were to get warmer.
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