Tech Challenge January – Answer
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Ready for the answer to January’s Tech Challenge? First, let’s review the question:
A reach-in 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. | 205 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. |
| Evaporator Superheat | 40 deg. F. |
| Compressor Inlet Temp. | 68 deg. F. |
| Total S. H. | 71 deg. F. |
| Ambient Temp. | 75 deg. F. |
| Room/Box Temp. | 51 deg. F |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | Low |
Answer:
The probable cause of the warm beer is likely to be a liquid line restriction. The temperature of the liquid entering the capillary tube is well below the ambient temperature, which tells 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. 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.
Cheers.
Dick
Posted In: ACCA Now, Tech Challenge
