Hot Milk

We have a warning light mounted on the outside of the milk house. This light is clearly visible from the house. I noticed it was on when they finished milking this evening so I went to investigate. I discovered the milk temperature was 50 some degrees, much to hot. So I did some investigating and discovered something in the systems brain isn't functioning properly. I manually started both compressors and they worked. So for some reason they are not receiving the signal to come on. In other words, the compressors think the milk is already cold. I have to go out and turn them off after while. If I don't, I will have a tank full of frozen milk.