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Saturday I went out to trouble shoot a Milk Cooler. There was a lot of ice forming on the bottom of the bulk tank and the compressor was running abnormally long. I put on my gauges and yes, it is low in Freon. I charged it appropriately. I ended up with normal condenser p/t for the ambient conditions and about 3° superheat at low load condition, (bulk tank @ 36°). That is what they want, a flooded evap to alleviate thermal stress on the cooling plates on the bottom of the tank. The condenser is a unique setup. I had to noodle over it a bit till it made sense. Starting at the compressor, the discharge line first passes through a free-heater (water heater with a desuper-heating coil in it), then it makes it's way back to the condensing unit and enters the condenser which has standard fan head pressure controls. Once it exits the condenser, it passes through a "suction line accumulator heat exchanger = aka SLAHX" and then on to the TEV. Through the TEV and on to the evap plates and then back to the SLAHX and back to the compressor suction port.
The TEV threw me for a loop at first. It is designed to maintain a specific subcool 10° at the condenser. In this manner it is possible to keep the condenser operating at maximum BTU output regardless of ambient conditions or evap loads. This is important because milk needs to be cooled quickly and the milk that is already in the tank should not be allowed to warm up during consecutive milkings.
So that's all good. Here is the problem. 245° to 250° comp discharge temp. It didn't seem to vary much with the suction line temp. Granted, the suction line picks up some heat going through the SLAHX but I was measuring temps both before and after to get a better feel for things. The comp is a Techumseh AGA5568EXN. That is a H/Back Pressure Air Conditioning compressor. I did notice the compressor's nominal capacity is about 9k BTUh higher than the max output of the evap, which occurs at the max rated influx of warm milk.
I will attach Pics. https://www.dropbox.com/sh/p871yhxaodphd8z/AAAc1VEK8ZCVUv1XFik4dPjna
Oh, and I did find 2 leaking service ports which account for the low charge.