York Centrifugal Chiller-No Oil Return

[bunglebear]

we have some old R11 chillers in a big office building. One of them is causing problems as it is going out on low oil pressure and seems to have done so a few times over the last few months. The sump sight glass is half full, until the oil pump is started to prelube the machine and then the sump empties. Compressor will run for just a few minutes and trip out. The oil filters were changed last week. The service guys were on site and having big problems. They tried to add oil to get the pressure up (didn't work) and they were going to drain it from the evaporator and recharge to the sump. Last week one of them did the service and left the valves on the oil line closed so it would have probably had an oil problem because of this, but it is impossible to get the oil back and stop the trip outs. The suction pressure I thought was high compared to the other two machines and the condenser pressure low (I can't remember but it was around 20kPa or perhaps that was in Hg). The oil pressure was dropping towards 50kPa where I would ahve been looking for 150-200, evan though on the running logs it has always been no more than 120kPa. I actually think the problem is the compressor (maybe a bearing) which is the cause of this but I'd be grateful for any input. Thanks

[txhvac]

Check & make sure your eductor (jet pump) is open, this skims oil off the top of the cooler & returns back to sump. the eductor is based on condenser pressure. Look @ the scavenger line drier, 2-3 degrees drop. Verify that the vent-line on top of chiller is closed on start-up could be stuck open, line opens to vent refrigerant back to chiller from oil circuit, if open at start-up, oil pressure is higher than barrel pressure, you will lose oil pressure. You can add oil to try & get it oil back, but if your eductor is not returning oil you won't get anything back. Yes, worse case senario you could have a bearing issue, I'd check few more things before getting ready for a bearing repair. Hope this helps.

[bunglebear]

Check & make sure your eductor (jet pump) is open, this skims oil off the top of the cooler & returns back to sump. the eductor is based on condenser pressure. Look @ the scavenger line drier, 2-3 degrees drop. Verify that the vent-line on top of chiller is closed on start-up could be stuck open, line opens to vent refrigerant back to chiller from oil circuit, if open at start-up, oil pressure is higher than barrel pressure, you will lose oil pressure. You can add oil to try & get it oil back, but if your eductor is not returning oil you won't get anything back. Yes, worse case senario you could have a bearing issue, I'd check few more things before getting ready for a bearing repair. Hope this helps.

I do know that after the service was done, the eductor was left closed so all the oil pumped out. \This is open now but no oil return still. The scavenger line must be called something else here so assume it is the one at the top of the chiller rather than the one at the bottom of the condenser barrel ????
Oil pump raises pressure on pre lube but drops back on start up and stays low.

[Randy S.]

Be sure the gas line into the eductor is clear. I've seen a flake of rust or paint stop the oil return from working. Valve it all off, and take the line loose on both ends.

I've also had the oil pressure relief stick open, and dump all the flow down the bypass, and back to the tank. You can tell by the temperature of the bypass between the relief and the tank.

[toptwo]

what kind of machine carrier, york, or A Joy compressor unit

[toptwo]

oops didnt see it was a york.

[stickerhead]

If it has a Turboguard purge, the check valve from the foul gas line may be leaking back and dumping the oil into the condenser. If it is slowly losing oil, the oil eductor system is not working. This could be a sign of low refirgerant charge. Remember, the oil eductor works best at part load because the eduction point is between the vanes and the impeller. Make sure the condenser gas to the eductor is not overdriving the eductor. Sometimes when it is open too far, it will blow gas by.