Oil return problems

[Peter_1]

Freezer store-room, installed 1994.
Original situation: 2 independent Copeland Demand-cooling compressor (R22) on 2 KUBA evaporators, electrical defrost. Danfoss TE5.
No oil separator nor suction accumulator.
2 HE’s in the discharge for make-up water for the ground heating.
Since the install no big problems. (broken heater in the evaporator, condenser fan fault,…)

Round March this year, one compressor went in fault. Piston was broken.
Reason??
Client does minor repairs themselves and sometimes when a heater in the evaporator is broken, they wait to repair it till they have 2 or more broken heaters or unit is completely frosted.
Possible cause: ***** washout in the sump??

Installed a new compressor, standard compressor (no demandcooling) and retrofitted to R404a. Blow out the lines (+/- 80 to 100 ft) with OFN. Let it run on POE and replaced after 4 hours running with new POE.
After 1 day, replaced oil again.

Appr. 10 days later, call from clientà New compressor went in fault.
Cause: broken pistons.
No oil in sump.
Searched for fault: tech had installed a new TE5 and installed an orifice 3 instead of a 1.
***** washout.

Installed new compressor. SH within the limits (20 K measured at inlet compressor)
After 1,5 months running, again strange noise (knocking metal noise) in compressor. It’s just like a piston is has too much spacing. Again, almost all the oil has gone out of the sump.
Checking Oil Safety device: wired wrong by ‘someone’

Is oil return so worse with R404a compared with R22?
Speed in the suction lines is approximately the same.
We did retrofits in supermarkets with more then 2000 ft of lines and never had those problems.
Also never had oil return problems with R22, at least no such a problems.

Installing an (coalescent?) oil separator?

[stan1488]

mornin Peter! i would check evapps clear , clean, sh, install standard oil separator, sounds like key is unclear(icing) coils ecessive run times low sh and velocity, parralel compressors or independent compressors? if parr. which stage problem?

[chemi-cool]

Hi Peter.

In all the oil problems I had, always after changing the orifice to a smaller one and installing oil separator, problems has gone.

One more thing you can do is making a 1/4 pipe with SV from the lower point at the collector pipe at the evaporator to the suction line operating via a timer controlled by the compressor main contactor.

I have done this on a unit where the evaporator wes 20m below the condensing unit. No oil problems there anymore.

Chemi

[Peter_1]

Thanks already, just a quick reply while eating


2 independent compressors and evaporator is +/- 4 m above the compressor, lines sloped towards compressor.

[chemi-cool]

Bon appetite Peter.

Still, check the evaporator design and see how the pipes are arranged.
The oil is there somewhere.

Chemi

[Peter_1]

That's true and it only can be in the pipes or evaporator.
But why weren't there any problems during almost 10 years with R22? That's bothering me now.