May 2017 Tech Challenge Answer
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A commercial rooftop utilizing R-410A with a TXV feed device (and receiver) has a customer complaint of “insufficient 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. | 236 deg. F. |
| Condensing Press./Temp. | 442 psig / 124 deg. F. |
| Condensing Outlet | 112 deg. F. |
| Condenser Sub cooling | 12 deg. F. |
| Condenser Split | 36 deg. F. |
| Entering Feed Device Temp. | 89 deg. F. |
| Evaporator Press./Temp. | 125 psig / 43 deg. F. |
| Evaporator Outlet Temp. | 52 deg. F. |
| Evaporator Superheat | 11 deg. F. |
| Compressor Inlet Temp. | 68 deg. F. |
| Total S. H. | 25 deg. F. |
| Ambient Temp. | 88 deg. F. |
| Room/Box Temp. | 78 deg. F |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | High |
And The Answer is…
The problem appears to be a restricted air flow over the condenser caused from a dirty condenser, diverted air flow or condenser fan issue. The condensing pressure/temperature, and condenser split are high to expel the heat gained in the evaporator, superheat and compressor. The high compression ratio is causing recompression, high discharge temperatures and high amperage. The subcooling and superheat are high to normal because the TXV is attempting to maintain a constant S.H. with a lower refrigerant flow caused by the higher compression ratio.
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