frascold compressor out of oil

[DEVIL]

Hello

I had a litle troble with a frascold compressor semi hermetic, somewhere at 13 Kw of cooling , i whas qurios if someone happend the same

it's a cooling room made by me abaout one year ago, and it whasan't worcking, when i got to the sight, i doscoverd that the compressor, whas not turning, and there whas no oil in the sight glass, after short start and stops, i managed to make the compressor turn again, and when on with the short start and stop, so i can get the oil back to the compressor, after 5 mins, the sight glass whas complitly full with oil. I'm qurios if someone did encauntered the same problem, now the compressor work's ok, (i'm qurios for how long but now it's ok), but i didn't manage to answer myself the question where whas the oil, now it's worcking for a period of hours, and the sight glass is full with oil.

Sorry for my english

[mohamed khamis]

Unfortunately I could not understand well ur writting. But basis on my comprehension for ur problem, the oil migrated from the compressor to the evaporator and piplines and entrapped there during the off period (may be rather long) and the reasons for its migrations perhaps:

1- the compressor location is above the evaporator and there is no oil traps or oil separators to get back

2- the compressor is located in warmer area that evaporator location.


These are only speculations, more description of ur system will help more.

Cheers

[Brian_UK]

yes, sounds as though the oil is not getting returned properly during normal running.

Do you have an oil separator fitted?

Are there oil return traps?

Is the pipe sizing correct?

Does the unit run at low load for long periods, this will allow the oil to stay out of the compressor?

What sort of defrost system is fitted?

[protect]

Hallo,

hat kind of oil protection are you using within the compressor? Differential pressure?
The application is a rack unit or single compressor.

[mohamed khamis]

yes, sounds as though the oil is not getting returned properly during normal running.

Does the unit run at low load for long periods, this will allow the oil to stay out of the compressor?

What sort of defrost system is fitted?

Hi Brian_UK

As my knoweldge if the unit is overdesigned, at low loads it runs shortly and this impedes the compressor to get back its oil from the system, this is called short cycling problem. As a result of a short running and long off-cyling (because the load is relatively low) the oil is entrapped in the system and cease to flow back to compressor and thus the compressor loses gradullay its crankcase oil level, am I wright or rong.

Cheers

[DEVIL]

the pipe size, is ok, there is no need for oil traps, because, the evaaporator is slightly above, and the piping respects all ther rules, and after working for 1 minute, the cranck case is full with oil, mutch above the minimal limit, so ... all the oil returns normaly, it worcked for some period of time, and i whas watching it, becuase i whas makeing anather cool rom, in a nearby building, and the oil lever whas allways good, actualy is very good, it whas never even close to the minimum, so ... i don't getit why it happend.

[Gary]

It is possible for refrigerant to migrate to the evaporator during the off cycle. If the evaporator is above the compressor, liquid refrigerant in the evaporator then travels by gravity down the suction line to the compressor where it washes the oil out when it starts. The suction line should loop above the evaporator and then down to the compressor, thus trapping any liquid refrigerant in the evaporator.

[DEVIL]

Gary, might be right but not in this case, whe allways fit eletromagnetic valves, that are closed when the compressor is in the off cycle, so ... refrigerent migration in the off cycle, is excluded