May 2015 Tech Challenge – Answer
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A medium temperature cooler utilizing R-134a with a fixed orfice (capillary tube) feed device has a customer complaint of “warm product.” The symptoms at the convenience store confirm warm product and the condensing unit appears to be cycling on the low or high pressure control. What are the “possible causes” with the following measured conditions on this field service check sheet?Field Service Check Sheet
| Compressor Discharge Temp. | 200 deg. F. |
| Condensing Press./Temp. | 112 psig / 94 deg. F. |
| Condensing Outlet Temp. | 78 deg. F. |
| Condenser Sub cooling | 16 deg. F. |
| Condenser Split | 19 deg. F. |
| Entering Feed Device Temp. | 44 deg. F. |
| Evaporator Press./Temp. | 5 psig / -3deg. 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. | 50 deg. F. |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | Low |
And the answer is…
The possible causes of the warm product are likely a liquid line partial restriction. The temperature of the liquid entering the TXV is well below ambient tells us that some evaporation has taken place before it got to the TXV. If the liquid line and filter/drier are also cold, a partially restricted filter/drier is probably the culprit. The pressures and amps are low 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.
Posted In: ACCA Now, Tech Challenge
