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July 2014 Tech Challenge Answer

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A split air conditioner that has been retrofitted from R-22 to R-438A (M099) with a TXV metering device (and receiver) has a customer complaint of “warm, no cooling”
The condensing unit appears to be running 100% of the time. What are the “possible causes” (Note: The unit was retrofitted per the manufacturers guidelines and there is only one problem intended) with the following measured conditions on this field service check sheet?

Field Service Check Sheet

Compressor Discharge Temp. 220 deg. F.
Condensing Press./Temp. 195 psig / 95 deg. F.
Condensing Outlet Temp. 81 deg. F.
Condenser Sub cooling 14 deg. F.
Condenser Split 10 deg. F.
Entering Feed Device Temp. 81 deg. F.
Evaporator Press./Temp. 50 psig / 32 deg. F.
Evaporator Outlet Temp. 51 deg. F.
Evaporator Superheat 19 deg. F.
Compressor Inlet Temp. 75 deg. F.
Total S. H. 43 Deg. F.
Ambient Temp. 85 deg. F.
Room/Box Temp. 80 deg. F.
Compressor Volts 240 V.
Compressor Amp. Draw Low

And the Answer is…

The possible Problem is a partially restricted TXV Inlet creating a very low refrigerant flow rate and causing the evaporator, Compressor and Condenser to be starved of refrigerant. This results in low suction and condensing pressures, high superheats and low amperage draw. If the sub-cooled liquid entering the Freezer is above ambient temperature(which it is), there has been no flash off of liquid refrigerant prior to the TXV and the restriction is likely a plugged screen at the inlet of the TXV. Since the symptoms for an undercharged system are very similar, many may have listed this as the possible cause, and the main difference is that with an undercharge, there would be lower sub-cooling levels. 

Posted In: ACCA Now, Tech Challenge

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