try again

[hem057]

this is a 9RB1 0760 TFE Copeland compressor, and I should mention that there are two compressors, each tied in with two evaporators each, totally independent of one another,
freezer application, both with 408a refrig. and the oil failure is tripping, HOT GAS DEFROST, I have been in many times and never catch it tripping, 3 weeks ago changed the contactor, have now changed the valve plate (wed this week), and the oil failure control (yesterday) and the unit is still off every morning, when it is operating suction is 15, oil pressure discharge is 70 (means oil net is 55) everytime I am there oil level is good, from 1/8 to 3/4 sightglass,I have never seen excess foaming,
so if this is bad blow by, I should see excess faoming, thrashing, if oil is not returning, I would see lack of oil in sight glass, if we had liguid flooding back from evaporator, I would see this in alot of foam in oil,...
or even a bad control, now is a new one,
what am I missing, any suggestions
I should mention that the lower unit never trips anymore, I changed the valve plate over a year ago because of a tripping problem back then, never did it again,

[rimek]

Now that it is happening every morning(that's different than your last post- so all your labor has changed something, might be easier to troubleshoot if it has become that consistent), have you tried skipping that overnight defrost to be sure that's what causes it to trip?
Does this unit use a defrost termination stat, is it working?
How does the compressor sound during defrost and regular run?
How long is hot gas defrost?
Is this an air cooled unit?
Is there any thermobank-type loading to keep hot gas supply up?
Does the condenser fan(s) cycle off in defrost?

Sounds like you've checked the ops fittings for crap. I didn't hear sentronic either so I'm assuming it's a regular johnson/penn type?

For the amount of time this is sucking up, put a cheap clock on it to find out when it trips exactly(sensaphones are cool for this-use alarm contacts on ops and it will call you or your machine when alarm sounds, giving you a time stamp) and get there at that time the next overnight to witness "phenomenon".
Ya, it's after hours and all, but you're running out of parts to change.

[rocket]

net oil pressure is NOT oil pump outlet minus suction
it is oil pump outlet minus crankcase pressure

blowby is suction pressure compared to crankcase pressure
this may be your problem

[hem057]

I didn't go into all the details on this post, but I have put gauges on the suction service valve at the compressor inlet and the actual port where the oil pressure failure line is coming out of the compressor body, and they were both reading 15 psi suction, therefore the terminology, sorry about not being more specific
I may have to pick up a guage with larger graduations to read more accurately what the pressure difference is between the suction and crankcase, but on the guage/hose set we are using, they look the same