Oil Pressure safety scenario
I've got a 7-1/2hp condensing unit serving 9 doors of freezer merchandiser. For almost a week now, every morning the dern thing is off on oil pressure safety.
This is what I have done:
1. The system was low on refrigerant, added R-408A, cleared sightglass.
2. The defrost timer was wired to directly de-energize the compressor relay. I re-wired the timeclock to pump-down on defrost initiate, and assured that the lock-out relay for the heater circuits was properly configured.
3. Checked oil pressure, got 20 to 30 psi. (safety set for 9psi).
4. Replaced oil pressure safety after it failed to reset (not because it kept tripping)
5. other responses to the scenario included some faulty wire connections in the control/safety circuit.
... Now the equipment is OLD, and likely misapplied. I have advised mister customer that I recommend not dumping thousands of dollars into this sytem for repairs, so I have been going at this step by step.
On occasions that we arrive at the site with the unit down (safety tripped) the crankcase is full of fluid (lubricant/refrigerant). I was anticipating liquid refrigerant in the crankcase oil, which is why I endeavoured to configure the pump-down properly (the store personnel had gotten into the bad habit of going on the roof and puching the "reset" button).
The unit went down again this morning. My next step is to
1. evaluate adjust superheat (and probably the expansion valves are misapplied)
2. The wiring is a mess, and we are unaccounted for voltage from the case (presumably the 200v supply to the case is supplied from the CU for the fans and heaters, but when the CU disconnect is de-energized, we still have a live 120V leg coming up from the box. I think that somewhere the 120V light circuit is crossed into the CU wiring scheme. I have essentially removed the thermostat from the circuit, becuase none of the wires coming from the cases are marked and I was saving the wiring work until I was certain that the compressor was going to survive.
....But the safety keeps tripping, and I have yet to find any oil pressure discrepancy..... the compressor (a Copeland Semi-hermetic) is knocking like a wrist pin is worn (confirmed by acoustical characteristics under differing head pressures... i.e. knock-knock-knock-knock-knock. knocking diminishes when you increase the head pressure by blocking off the condenser coil.
What do you think?:confused: