Tech Challenge – July 2018 Answer
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A rooftop utilizing R-410A with a fixed orifice metering device has a customer complaint of “no 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. | 225 deg. F |
| Condensing Press./Temp. | 292 psig / 94 deg. F. |
| Condensing Outlet | 88 deg. F. |
| Condenser Sub cooling | 6 deg. F. |
| Condenser Split | 7 deg. F. |
| Entering Feed Device Temp. | 88 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. | 87 deg. F. |
| Room/Box Temp.34 | 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 picking working. The high evaporator temp/press is probably caused by an inefficient compressor that is not pulling refrigerant from the evaporator and the evaporator is not picking up much heat. The next step is to before condemning the compressor is to perform a compressor efficiency test to manufacturers specifications.
Posted In: ACCA Now, Tech Challenge
