July 2017 Tech Challenge – Answer
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A freezer utilizing R-402A with a TXV metering device (and receiver) has a customer complaint of “warm case.” The symptoms at the store confirm that the case that normally operates about 0 degrees is 34 degrees and the condensing unit is 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?et?
Field Service Check Sheet
| Compressor Discharge Temp. | 240 deg. F. |
| Condensing Press./Temp. | 204 psig / 90 deg. F. |
| Condensing Outlet | 87 deg. F. |
| Condenser Sub cooling | 3 deg. F. |
| Condenser Split | 5 deg. F. |
| Entering Feed Device Temp. | 86 deg. F. |
| Evaporator Press./Temp. | 48 psig / 14 deg. F. |
| Evaporator Outlet Temp. | 36 deg. F. |
| Evaporator Superheat | 22 deg. F. |
| Compressor Inlet Temp. | 54 deg. F. |
| Total S. H. | 40 deg. F. |
| Ambient Temp. | 85 deg. F. |
| Room/Box Temp.34 | deg. F |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | Low |
And the answer is…The possible cause appears to be an inefficient compressor. The head pressure is lower and the suction pressure is higher than normal with a very high discharge temperature caused by the recompression of gases. The TXV is wide open, but there is very low refrigerant flow causing maximum subcooling (to with-in 2 deg. of ambient) and high superheat. The amps are low because the compressor isn’t working. A compressor efficiency check per manufacturers specifications needs to be accomplished.
Posted In: ACCA Now, Tech Challenge
