I have a blast freezer with a problem of one of the two condensing units shutting off on low pressure after a couple of hours.
It is a basic system of two Zannotti condensing units with one evaporator with two sets of passes keeping the two units separate. there is a solenoid before the Danfoss TES20 mop expansion valves and condensing units are controlled by the high and low pressure switches. I have checked the oriface spring lengths are both the same and expansion valve vials are at same height on suction pipes. Both systems have full charge of 404a and I have condensing fans set at 20 bar on both units. I think problem can only be at expansion valve and I have opened it and it had a waxy deposit. A year ago I changed the compressor oil and used Emkarate RL32H and wonder if this oil is ok evaporating at minus 40c. I did just fit two new core driers and not getting to bottom of problem. All evaporator fans are working and so are all the defrost heaters. At start on pull down both systems have the same low pressure but after a few hours the low pressure drops away on one condensing units and it cycle on and off on Low pressure. Any advise will be greatly appreciated