This was an after hours call. The low temp alarm was set off on compressor 1 oil failure when the sight glass is full. I decided to read up on the past service reports.
Past technicians found that the compressor was running out of oil due to a very oversized suction line. Its 2 1/8" when it should be 1 1/8". Compressor 2, 3, 4 only come on after defrost when the oil is coming back. That is why there is always a full sight glass. Compressor 1 will trip and 2 will come on pumping oil out of the oil separator refilling compressor 1. That is why there never seems to be a problem.
The low temp rack alarm system had to be reset before leaving.
