oil sludge accumulation in R-22 rack compressor?

[beachfronttech]

Hi to everybody and Happy New Year. I have one question for the pros:
In supermarket rack systems, is it unusual to have the last compressor in the oil return circuit accumulating a lot of sludge? There is this particular compressor located at the end of the rack line which continuously displays darkened oil. Even after an oil change, the color of the oil in the sight glass changes quite rapidly from typically clear yellow to brown. Would an in-line filter drier be any helpful?

[nike123]

Hi to everybody and Happy New Year. I have one question for the pros:
In supermarket rack systems, is it unusual to have the last compressor in the oil return circuit accumulating a lot of sludge? There is this particular compressor located at the end of the rack line which continuously displays darkened oil. Even after an oil change, the color of the oil in the sight glass changes quite rapidly from typically clear yellow to brown. Would an in-line filter drier be any helpful?

Did you check discharge temperature of that compressor?

[beachfronttech]

Thank you for your reply. Discharge temperatures vary depending if the system is in defrost mode or not, but the highest one I´ve been able to record is about 245 degrees F ( 118 degrees C). These compressors are all Copeland Discus, with head cooling fans and Demand Cooling Modules installed. Additionally, the compressor located next to the last, which performs under similar conditions, keeps a very neat oil color.

[nike123]

Thank you for your reply. Discharge temperatures vary depending if the system is in defrost mode or not, but the highest one I´ve been able to record is about 245 degrees F ( 118 degrees C). These compressors are all Copeland Discus, with head cooling fans and Demand Cooling Modules installed. Additionally, the compressor located next to the last, which performs under similar conditions, keeps a very neat oil color.

That is pretty high! Typically, maximum discharge temp. should be 225°F (107°C)
Check superheat!
What refrigerant is in system (I see now in subject:o), and what is evaporation temp, for that application.

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[joshman1]

I suspect your compressor is faulty, do a complete mechanical (compression) check, how is the oil filter on drain plug or is the dirty sight glass misleading?, check the colour of your valve heads. Good luck.

[Tesla]

If the oil return is common to compressors on rack, the sludge could come from the system - other compressor(usually valves) or moisture. There should be a filter of some sort in the common oil return pipe. Use an IR thermo to check crank and valve temps, compare with other comps. Oil entry to comps level - check with clear thin hose. Even if oilfloat valves are used, if there is a pressure differance between 1st and last or a slope the sludge is more likly to deposite in the last compressor. Is the last comp the least used? I have also noted this problem with some ac chiller racks.

[s/market guru]

check the efficiency of compressor first,you may have done a valve plate and have discharge bypass into sump causing oil discolouration

[750 Valve]

Also if its a rack check there is no suction sock left in the filter housing, I have found this before - that particular comp was pulling a vacuum as the rack only had a common LP safety piped off the header and had massive superheat and really discharge temps - it was cooking the oil.

Also is it the comp with the most run hours by any chance as there may be a common issue its just it shows up in this one first.


Like the guru suggests - have you done a valveplate? Is it a LT rack? by the disch temps it sounds like it - they are pretty darn high, are the crankcases equalized? what is the oil level control? What sort of filter is in the oil circuit? We only use sporlan ROF replacable cartridge filters - they are pretty good performers... ya gotta filter that oil!

[s/market guru]

its either a valve plate or your demand cooling is not working mate

[beachfronttech]

Thank you for all your time and interest. I must add that the compressor´s log card reports a recent oil pump gasket change. I remember that these Discus compressors use only two kind of gaskets: one with a rounded hole and the other with a square-like hole on it, depending on the model. Assuming that the gasket was not selected appropiately, could this situation be leading to the color change?
By the way, some of you suggested a compressor performance test: is that procedure done in the field or in a lab or test rig?