Tech Challenge – March 2012
A split A/C system utilizing R-22 with a fixed orifice metering device has a customer complaint of “no cooling.” The symptoms at the customer’s home confirm that the thermostat is not satisfied and the condensing unit and blower are running continuously. What are the possible causes with the following measured conditions on this field service check sheet?
Field Service Check Sheet
|Compressor Discharge Temp.||240 deg. F.|
|Condensing Press./Temp.||260 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.||88 psig / 53 deg. F.|
|Evaporator Outlet Temp.||58 deg. F.|
|Evaporator Superheat||5 deg. F.|
|Compressor Inlet Temp.||70 deg. F.|
|Total S. H.||27 Deg. F.|
|Ambient Temp.||80 deg. F.|
|Room/Box Temp.||84 deg. F.|
|Compressor Volts||240 V.|
|Compressor Amp. Draw||High|
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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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