Based on the information provided, this sounds like the more likely scenario to me.
Originally Posted by gearhead3
The crankcase becoming overfull and the pump locking out on oil sound like 2 separate issues with the first being a result of the second.
Unless you've got a suction accumilator on the rack, I'd be looking at the circuits nearest your pump as the culprit.
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Just went through all of this after a company did a refrigerant conversion on a Rack. Same time of night every 2 or 3 days there was an oil fail on a particular compressor. What we finally figured out what was happening, oil was logging in a couple of circuits at night due to low refrigerant velocities under low load conditions. This would cause the circuits to flood to the rack due to the insulation properties of the oil and low heat transfer of the evaps. Now, the case would go into defrost, oil is warm that is insulating the sensing bulb from the actual temps of the suction line.. and the circuits would flood hard trying to cool down evaporators full of oil. Now, this would wash oil from the compressor directly under this circuit, which only took about 5 mins after defrost ended. Then the oil would start coming back from the evaporators due to increased refrigerant velocities after defrost. So, everything would look good when a tech got there. Had to actually sit with it and watch it one night.
Ended up changing 37 TXV's, but it's been purring ever since.
Did any of that make sense?
I can't fix it if it won't stay broke..
It sure makes sense to me, a little low ref flow a little oil lodging a little blow by on the compressor equal big oil problems.
I wish we knew what type and size comp he has. It seems it worked fine till now of course could have been a long term prob he has just has gotten involved in.
If it has a helical separator it just will not work at light loads.
maybe the oil separator isnt doing its job
We had a very similar issue with a hill rack also about 10 years old. same senario low and med temp setup. off time for med temp and hot gas for low. ran fine for several years and all of a sudden the reservoir was empty and 1 compressor shutting off on oil failure. checked pump pressure when compressor was running 40-45 lb dif. dropped the float in the separator to see if there was a restriction and when we did almost no oil came out. usually if there is a restriction there should be enough oil to make a mess decided that the oil separator was not separating any oil. as soon as we changed the separator compressor running fine we actually had to remove a couple of gallons of oil sinse the oil was to the top sight glass
Glad to see you posted here for answers. Thanks for posting the solution.
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Last edited by dgruber; 01-06-2013 at 05:27 PM.
I would check how the suction group is set up depending on the operating system. I have had the same issue with CPC using there enhanced suction mode. If this compressor runs the most and is the only one at times it maybe coming back through the suction.