January Tech Challenge – Answer
A frozen food case utilizing HFC R-404A with a TXV metering device (and receiver) has a customer complaint of “warm product.” The symptoms at the convenience store confirm that the case is 20 degrees warmer than normal and the condensing unit appears to be cycling on the low pressure control. What are the “possible causes” (note: there is only one problem intended) with the following measured conditions on this field service check sheet?
Answer: The problem with this frozen food case centers on restricted air flow over the evaporator coil, most likely a frosted evaporator caused by a failed defrost system. With the frost insulating the load (heat) from the refrigerant the pressures and splits are low as well as the S.C. and S.H.
The refrigerant entering the compressor is barely above saturation and compressor flooding resulting in compressor failure could result. The normal amp draw is caused by the nearly saturated, high density refrigerant coming back to the compressor.
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