Refrigeration Mystery Oil Pressure Fault
Compressor keeps tripping off on low-oil-pressure indication but there is oil visible in the crankcase sight glass?
Or - There has always been an adequate oil level in the past and there is no evidence of an oil leak - so why, all of a sudden, would there be a low-oil-pressure indication?
What's going on?
It could be the evaporator coil is getting too cold for some reason - probably a loss of airflow. Check for reasons why the evaporator coil is running too cold.
Check belts condition, belt tension, dirty filters, dirty blower wheel fins, obstructed return-air or closed dampers.
Also check for proper operation of the expansion valve. It could be an expansion valve stuck open.
In the situation where the evaporator coil is running too cold, the oil will thicken as it passes through the evaporator coil and tend to stay in the coil. This can serve to deplete the oil in the compressor enough to trip the low-oil-pressure sensor.