Tech Challenge - March 2018 Answer - IE3: Business Tools for HVAC & Plumbing Contractors  

Tech Challenge – March 2018 Answer

A split air conditioner utilizing R-410A with a TXV feed device (and receiver) has a customer complaint of “warm, no cooling.” The symptoms confirm inadequate cooling and the compressor appears to be running all of the time and the thermostat is not 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. 230 deg. F.
Condensing Press./Temp. 296 psig / 95 deg. F.
Condensing Outlet 82 deg. F.
Condenser Sub cooling 13 deg. F.
Condenser Split 10 deg. F.
Entering Feed Device Temp. 85 deg. F.
Evaporator Press./Temp. 101 psig / 32 deg. F.
Evaporator Outlet Temp. 52 deg. F.
Evaporator Superheat 20 deg. F.
Compressor Inlet Temp. 75 deg. F.
Total S. H. 43 deg. F.
Ambient Temp. 85 deg. F.
Room/Box Temp.34 80 deg. F
Compressor Volts 240 V.
Compressor Amp. Draw Low

Answer: The problem appears to be a restricted TXV. The low refrigerant flow and inability to pick up heat in the evaporator is causing low discharge and suction pressures, low splits and high superheats. With low refrigerant flow and most of the refrigerant in the receiver and liquid line the subcooling is higher. The TXV is likely restricted with the formation of wax, caused by insufficient dehydration of the system during service. After the TXV is replaced or cleaned, the filter drier needs to be replaced and a deep evacuation performed that will remove all moisture and non-condensibles from the system before charging and doing a system check.

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