Centrifugal Oil loss to system

[setrite]

Hi Guys,

A Centrifugal, after a leak repair tripped due to low Oil level. Went to site, charged Oil, started machine and found discharge superheat very low at 0.5 Deg F. Recovered around 300 Kg of Refrigerant, now superheat is normal. But in a couple of weeks it again tripped due to same fault and oil went into the system. What could be the reason ? A leaking Eye Seal ?

manufacturer says chiller is out of warranty, Customer is furious says won't buy again.......

[Toosh]

Hi Setrite, it would be helpfull if we knew who the make and model of the centrifugal was.

Regards Toosh

[Lowrider]

Has the machine been surging before giving the oil alarm?

If so check flow and temperatures and temperature difference across the condensor.
Could be low flow, too hot water coming back or leaving the machine which will cause the machine to go in to surging and thus "sucking" the oil from the compressor!

[absrbrtek]

Ditto! Need more info.

Hi Setrite, it would be helpfull if we knew who the make and model of the centrifugal was.

Regards Toosh

[Lowrider]

After reading your post again, I have the following remarks:

A Centrifugal chiller normally doesn't have a large superheat, like a dx since it's an bath evaporator. One could expect the sh to be between 0 and 3K.

What gives a better clue as to the charge of such a system, is approach. That's the difference between evaporating temperature and leaving water. Make a complete report at the highest load possible, but at at least 70% RLA and post it here with make and model of the machine!

If you really want to be sure the charge is correct, reclaim all the refrigirant and charge the amount it's suppoust to have.

[absrbrtek]

He stated .5F Discharge SH. The machine is obviously carrying over with that kind of DSH.

Pulling and weighing in the charge is not normally feasable on a centrifugal. Nameplate charges will get you close, but are not always 100% acurate.

After reading your post again, I have the following remarks:

A Centrifugal chiller normally doesn't have a large superheat, like a dx since it's an bath evaporator. One could expect the sh to be between 0 and 3K.

What gives a better clue as to the charge of such a system, is approach. That's the difference between evaporating temperature and leaving water. Make a complete report at the highest load possible, but at at least 70% RLA and post it here with make and model of the machine!

If you really want to be sure the charge is correct, reclaim all the refrigirant and charge the amount it's suppoust to have.

[Lowrider]

You are right! Didn't read it carefull enough!

Stil if the machine leaked, one would expect who ever repaired it made sure he weighed in the right amounth of refrigirant, so taking out 300 kg of charge would make it undercharged!

So again, make up a report and post it here!

Another note! When you added the oil, did you take out the extra oil added?

[setrite]

Thanks for the replies, This is a VSD chiller. After the leak repair, there was no additional charge top-up. After a few weeks of operation there was a low Oil level problem, Oil was topped up, Oil returned back into the Oil sump ( So Oil eductor's OK ), excess Oil was drained, the filter drier in Oil return line was replaced, chiller was put back into normal operation. A fortnight later the problem was repeated. Went to site, checked and found Discharge Superheat which should be normally around 15 - 20 deg F is only 0.5 deg F. Hmmm... checked Evaporator sight glass and found refrigerant level is normal. But even then recovered 300 Kg of refrigerant just to improve discharge superheat. Checked the differential Pressure between Evaportor and Oil sump and found it to be around 4 psid at 50 hz, reduced frequency and found differential pressure reduces to 0 at 42 hz. As far as my experience goes it can be caused by a leaking impeller eye seal.

Any other checks to make, before the compressor is opened.

I don' think it carrying over now, the refrigerant level in the evaporator is low, and discharge superheat is normal after refrigerant evacuation, but the Oil loss problem while chiller is running is still there.

[absrbrtek]

This sounds like a York chiller? Is the oil in the sightglass tinted brownish and wavey looking? What model chiller is this? What refrigerant?

[setrite]

absrbrtek, your right, this is a YK using R134a. The Oil is clear and not discoloured or wavy.