Okay, looking for any insight that maybe I've overlooked here.

Customer had compressor (Copeland 9RS1-1505-THC) compressor that started to trip the oil pressure safety. Through troubleshooting, found TXV's were at fault, and were replaced (both of them on both evaporators). Superheats were normal, but compressor had be subjected to much flooding overtime. You could hear lower end problems, and recommended replacement of the compressor.

Customer then found a used compressor at another jobsite, that HE opted to have installed instead of new compressor. The original compressor that was removed had a serial number from 1990. This compressor found on another site had a 1983 serial number. (A step in the right direction, eh?)

Installed this replacement compressor. Oil pressure much better, no lower end noise from it. After startup, saw that the oil in the site glass was low. I said, I would have to return on Monday, would fill up then. (did not have any on the truck right then).

Over the weekend, this compressor tripped the oil safety. I thought, could be expected, since oil level was low. Added oil, on Monday. Ran great.... until

Friday morning, got the phone call again, tripped oil safety AGAIN. Customer had reset, and was running upon arrival. Pumped system down (shut off solenoid) Oil level went high on the site glass. Restarted, ran for a while, pumped down again. Oil level finished BELOW the site glass. Every pump down, the oil level was at a totally different level everytime.

Flo-Con head pressure regulator not working, and maintaining head pressure properly. It has a working crankcase heater (newly installed). Also has an oversized liquid line. (+20°F evaporator) which is 1 1/8". It appears for this line set run, it should only be about 5/8".

It appears that the compressor is passing a lot of oil into the system through worn piston rings and blow by. So, here's the question(s)....

1).Could the oversized liquid line be playing a part in not allowing the oil to consistantly return to the sump of the compressor?

2).Could the head pressure regulating valve not working properly also have that significant impact on the oil return?

The real answer I know is the compressor should be replaced with a new one that would not have this type of problem. But I'm just checking the "what if" department since the customer doesn't seem to want to spend any more money on this project.