Blow By Explained for Refrigeration Compressors

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When you get multiple calls to a store and the oil safety device like a Sentronic or CoreSense Protection is tripped and goes into alarm, on the same compressor that is not a nuisance trip. There is usually a reason it trips, and it is our job as refrigeration professionals to figure out what causes this alarm.
High discharge temperatures are very common in supermarket applications and when you have high discharge temperatures that start to thin the oil. When the oil is thinned it starts to lose its lubrication properties and you can start developing wear on pistons, rings, and cylinder walls.
To check a Discus compressor for a pressurized crankcase, compare the crankcase pressure to the suction pressure. If the crankcase pressure is higher than the suction pressure it would indicate blow-by. Typically this is the result of worn piston rings. However, a system using an oil float or discharge oil separator that is stuck open would also cause an increase in the crankcase pressure.
What you need to do is safely remove all the gas from the compressor and lockout the electrical, pull off the head or heads of the compressor, and check for any wear that could potentially be causing this.