January 2015 Tech Challenge – Answer
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A medium temperature cooler utilizing R-134a with a TXV metering device with receiver, has a customer complaint of “warm product.” The symptoms confirm warm product and the condensing unit is cycling frequently on the low pressure control. With only one problem intended, what are the “possible causes” with the following measured conditions on this field service check sheet?
Field Service Check Sheet
| Compressor Discharge Temp. | 192 deg. F. |
| Condensing Press./Temp. | 108 psig / 93 deg. F. |
| Condensing Outlet Temp. | 78 deg. F. |
| Condenser Sub cooling | 17 deg. F. |
| Condenser Split | 18 deg. F. |
| Entering Feed Device Temp. | 41 deg. F. |
| Evaporator Press./Temp. | 3 psig / -7 deg. F. |
| Evaporator Outlet Temp. | 37 deg. F. |
| Evaporator Superheat | 30 deg. F. |
| Compressor Inlet Temp. | 68 deg. F. |
| Total S. H. | 61 Deg. F. |
| Ambient Temp. | 75 deg. F. |
| Room/Box Temp. | 52 deg. F. |
| Compressor Volts | 240 V. |
| Compressor Amp. Draw | Low |
And the Answer is…
The problem is a restricted liquid line. This is verified by the entering feed device temperature of 41° F. (below ambient) caused by a liquid line partial restriction causing flash off (evaporation). The low side is starved giving high superheats and the high side follows the low side because the system is not picking up much heat. The discharge temperature is high because of the high superheated inlet temperatures and low refrigerant flow.
Posted In: ACCA Now, Tech Challenge
