Tech Challenge: November/December 2024
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A residential split A/C system utilizing R-410A with a fixed orifice metering device has a customer complaint of “insufficient cooling.” The symptoms confirm that the thermostat is not satisfied, and the condensing unit and 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. 240 deg. F.
- Condensing Press. / Temp. 283 psig / 92 deg. F.
- Condensing Outlet Temp. 87 deg. F.
- Condenser Sub Cooling 5 deg. F.
- Condenser Split 6 deg. F.
- Entering Feed Device Temp. 82 deg. F.
- Evaporator Press. / Temp. 145 psig / 51 deg. F.
- Evaporator Outlet Temp. 65 deg. F.
- Evaporator Superheat 14 deg. F.
- Compressor Inlet Temp. 76 deg. F.
- Total S. H. 25 deg. F.
- Ambient Temp. 89 deg. F.
- Room/Box Temp. 80 deg. F.
- Compressor Volts 240 V.
- Compressor Amp. Draw Low
Answer: The possible causes center on an inefficient compressor. The high discharge temperature is likely caused by recompression, low refrigerant flow through the system, and continuous compressor operation. The pressures between the high side and the low side have moved closer together, and the splits are low along with low amps, telling us that the system is not working very hard or to capacity. The system is flowing very little refrigerant, thus picking up very little heat.
The next step before condemning the compressor is to perform a compressor efficiency test relative to manufacturer’s specifications.
Posted In: ACCA Now, Tech Challenge
