York Chiller YCAJ Low Oil Pressure fault during pump down

I am a new commercial tech. I have a York Chiller model YCAJ160-46PA Serial 676AHL6A with two recip compressors . Circuit 1 compressor shuts down on low oil pressure during pump down only when the load is satisfied. When it runs, the oil PSID is identical to the circuit 2 compressor. I verified oil pressure with my gauges and matched to to microprocessor control. When we are in 60-70 degree weather, the load will satisfy and this is when I have the problems. When we get into the 80s and 90s , the system runs all day and night , all summer long with no problems because it never shuts down. I also checked and matched all transducers and temp probes. I cleaned the coils and checked proper superheat and subcool fully loaded . Why does this happen during pumpdown only? Other techs think the microprocessor is not supposed to be checking oil pressure during pumpdown. Any ideas

Did u check oil heater ? Pls run the comp at full load to oil return back.........

Hi Air tech

The microprocessor looks at the differential between suction pressure and oil pressure.
And calls that "Oil Pressure"!
There are many reasons why the oil pressure drops.
How you matched to your gauges I am not sure.
It is also operational level related.
Try maintaining a higher oil level and if that does not work. Drain the oil and check the oil strainer and sump for cleanliness.
J & P compressors love having load and work well, however as referred to above at continual low loads the throw oil for a pastime. Until the system is loaded and gas volumes rise the oil stays out in the system.
Which is what nuwan is referring to.

There are more things you can do but as I am not sure you are still with us?
I will defer that.

I checked my oil pressure at the pump with my gauges , subtracted from my suction pressure I had on my gauges and got my net pressure which matched the PSID on the microprocessor . I checked the crankcase heater amp draws and felt the compressor which was warm when off. I am still learning so I know It may seem like I ask stupid questions but my question- Is the only way to run the compressor fully loaded would be to lower to leaving water temp? Or is there another trick? Also I was told this compressor failed about 5 years ago. It was rebuilt by a local company and it failed shortly after. Our company had it rebuilt again by a different company and it has been working since then , kind of. The tech that I took this over from said that it has some nussance trips in spring and fall and all I have to do is reset it. So apparently it has been doing this for about two to three years. The oil levels in the sight glass is half full on one and about three quarters on the other. It is frothy when running which makes me think refrigerant is in the oil. I have been wanting check the strainer which I do not know how to but my boss does not want to get back into it at this time.

Air Tech,
In your first post you mentioned oil pressure may not be checked in pumpdown.
I would say that be incorrect, as it should be monitored at all times when running.

If it only happens in pumpdown suggest you simulate that to see what happens.
Watch oil for foaming & oil level.
Check compressor unloading if it has any & how it works within system.

See if anything obvious.

Can you swap compressors around, does it happen then as well?

My next visit to the job I am going to see if I can swap the compressors at the microprocessor which should tell me if it is the board or the compressor. The oil does foam up and is half full at site glass. Refrigerant in oil?