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Tech Challenge November 2020 – Answer

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A commercial split heat pump system, in the cooling mode @ 88° F. outdoor ambient, utilizing R-410A, has a customer complaint of no cooling. The system has TXV metering device’s on the indoor and outdoor coils with check valves. The symptoms at the home confirm that the compressor and indoor blower are running continuously. What are the “possible causes” (note: there is only one problem intended) with the following measured conditions on this field service check sheet? Note that in the cooling mode, the condenser is the outdoor coil and the evaporator is the indoor coil.

Field Service Check Sheet

Compressor Discharge Temp.  109 deg. F
Condensing Press./Temp.  295 psig / 94 deg. F.
Condensing Outlet  90 deg. F.
Condenser Sub cooling  4 deg. F.
Condenser Split  6 deg. F.
Entering Feed Device Temp.  88 deg. F.
Evaporator Press./Temp.  101 psig / 32 deg. F.
Evaporator Outlet Temp.  36 deg. F.
Evaporator Superheat  4 deg. F.
Evaporator Split  48 deg. F.
Compressor Inlet Temp.  40 deg. F.
Total S. H.  8 deg. F.
Ambient Temp.  88 deg. F.
Room/Box Temp.  80 deg. F
Compressor Volts  240 V.
Compressor Amp. Draw LOW

ANSWER: The problem appears to be restricted air flow over the evaporator (indoor coil) possibly caused by a dirty air filter. The low air flow is not allowing the load to be absorbed in the refrigerant, so the pressures and splits are low as well as the S.C. and S.H. The refrigerant entering the compressor is barely above saturation and compressor flooding resulting in compressor failure could result. The amperage draw is low due to the low load.

Posted In: ACCA Now, Tech Challenge

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