Please excuse my terminology for I come from an electrical background. We have one ammonia compressor that the motor has a hard time starting. The compressor inertial load seems to be greater than designed for the motor. The motor, compressor bearings and slide valve can be eliminated for this problem due to extensive troubleshooting.

The compressor is stopped now and has been off for a couple of days. The liquid ammonia injection for compressor cooling is frosted up. None of the other shut off compressors is displaying any frosting up and are in fact ambient room temperature.

The piping: First is a shut off valve then a check valve then a solenoid then a window then a regulator then shut off valve and then compressor entry. There is heavy frost at the window and between the solenoid and regulator.

I do not believe this frost should be there since the compressor is turned off and not requiring any cooling. Is it possible that liquid ammonia is being injected into the compressor when off thus causing the motor to see a heavy load during start. The motor only sees a too heavy of a load during start and not run. Any ideas of what is going on here? Also, what should one see in the window when the compressor is off or when the compressor is on. Thank you for any and all responses.