I have an upright Sanborn 60 gallon compressor. Model SLA 7006056 With a 755H pump. Running on 220. Older used compressor. I have had it a couple years. It is labled 10w30 synthetic and that is what I am using. Oil level is fine. It has been cold out the last couple months, under 30. The other day I went into the garage and the breaker was tripped. I reset it and the compressor built pressure and cycled fine several times. It does not struggle to start when cold. Nice quick torquey startup. After a while the compressor cycled, ran for a while, heard a clunk and then a belt squeal. I flipped off the breaker. Will look at it later. Well later came, I took the belt cover off and spin the pulley. It spins free. (normal) Turn the breaker on and it is running fine again. I am timid on using it. 2 strikes and all.... I guess I can take the pump apart and give it a once over. Ideas??