Tech Challenge March 2021 – Answer
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A medium temperature cooler utilizing R-134a with a capillary tube feed device has a customer complaint of warm beer. The symptoms at the convenience store confirm inadequate cooling and the compressor appears to be short cycling on the high or low pressure control. What are the “possible causes” (Note: There is only one problem intended) with the following measured/calculated conditions on this field service check sheet?
Field Service Check Sheet
| Compressor Discharge Temp. | 210 deg. F |
| Condensing Press./Temp. | 108 psig / 92 deg. F. |
| Condensing Outlet | 76 deg. F. |
| Condenser Sub cooling | 16 deg. F. |
| Condenser Split | 17 deg. F. |
| Entering Feed Device Temp. | 44 deg. F. |
| Evaporator Press./Temp. | 5 psig / -3 deg. F. |
| Evaporator Outlet Temp. | 37 deg. F. |
| Compressor Inlet Temp. | 68 deg. F. |
| Total S. H. | 71 deg. F. |
| Ambient Temp. | 75 deg. F. |
| Room/Box Temp. | 50 deg. F |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | LOW |
Answer: The possible cause of the warm beer are likely to be a liquid line restriction. The temperature of the liquid entering the capillary tube are is well below the ambient temperature is telling us that evaporation has taken place before the feed device. If the liquid line and filter/drier are also cold, a partially restricted filter is probably the culprit. The pressures and amp draw are low and it is cycling on the low pressure control because the liquid line is a very small evaporator and it is not picking up very much heat. The system is not working very hard and what work it is doing is in the wrong place.
Posted In: ACCA Now, Tech Challenge
