Oil foaming

[Mervin]

After recent compressor failure on low temp rack we’ve replaced oil protection and oil return controls then found it nessesary to change oil in system as clogging strainers etc from compressor debris I assume , now we have an issue with the oil appears to be foaming up within compressor and diluting the oil pressure yet as soon as it stops oil filling reaches level and stops filling looks good but restart oil foams again !do you think we must have excess liquid refrigerant entering via suction line ?

[passandscore]

Hi Mervin,

That could be the problem. What is your superheat?

[Aussie134a]

Yep liquid flooding back will cause the oil to foam and eventually freeze which ends up tripping oil safety's etc. Check TXV sh's

[Mervin]

Yep liquid flooding back will cause the oil to foam and eventually freeze which ends up tripping oil safety's etc. Check TXV sh's

I agree ,there appears to be no liquid refrigerant flooding, cold return ,not frosting ,the oil level compressor is at it should be but the return oil from reservoir is hot and appears like it’s infused with gas !when trxoil opens to fill ,the in rush of hot oil appears to froth up the sump oil ,we have had to throttle the return line so when traxoil float opens it’s only allowing a trickle of oil so as not to upset the sump oil ,it’s like the oil is too thin !if we purge some return oil at the traxoil it’s like a highly beaten egg white ready for the pavlova .ive checked and confirmed the oil is suitable but it’s either not mixed well with the residual oil in system or it is not handling the discharge temp ! ? Befrore the oil change the oil level floating indicators would rise and fall with liquid level but not now so it makes you wonder how the traxoil floats can operate properly

[al]

Have you semi hermetic compressors? Check that valve plates are ok, could have discharge gas passing back to compressor sumps, is oil return float stuck open in seperator? Sweating is normal on low temp packs, what is suction superheat, are you using 2 stage compressors? If so is interstage cooling valve ok?

[RANGER1]

Mervin,
Sump heater, is it working when compressor off?
Oil return should be very slow & controlled, also should not be all the time otherwise something else like what Al mentions above.
Is oil reservoir or oil separator for this compressor only & at discharge pressure? or is it a central reservoir from other compressors as well, if so it is vented to a lower pressure usually.

other things like following can help paint a better picture, as we can only speculate.

type of system & temperatures required (freezer. cool room. water chiller, air con etc).
refrigerant & oil type
suction pressure
suction superheat at compressor suction stop valve area
compressor discharge pressure
oil pressure & trip setting
sump oil temperature when running

[Mervin]

Hi thanx for your advice ,I thought you had it when ou advised maybe a valve plate fail causing high sump temp affecting the oil ,but all ok .i confirmed no liquid flood back and found the opposite ,I needed to open a few tx valves to reduce superheat which in turn reduced sump temp ,when oil temp came down a little it started to behave like it should the the traxons could open and close to control oil refill without foaming ,I believe it is the oil we used did not operate well at the higher temp ,extol psr 32 but I will see how it goes .ithink we may have some debris through system from the comp fail ie in tx strainer etc ,to answer your questions it’s typical lokbtemp supermarket rack three semi copeland comps one of which is variable speed ,-25 suction ,40 cond ,sump heater ok ,no mech float involved ,direct oil return to each traxon control ,

[RANGER1]

Mervin,
Thanks for letting us know what you found.