low oil after evacuation

[dave fulton]

We have a Carrier 19dk 360 ton chiller that seems to have lost half of its sight glass oil after we pulled it down. The oil agitates while the vacuum is on. Did we pull oil out to the tank because of a bad compressor seal, or is it boiling out because the oil heater was/ stiil on, thus raising the vapor pressure of the oil?:anyone:

[cperk]

We have a Carrier 19dk 360 ton chiller that seems to have lost half of its sight glass oil after we pulled it down. The oil agitates while the vacuum is on. Did we pull oil out to the tank because of a bad compressor seal, or is it boiling out because the oil heater was/ stiil on, thus raising the vapor pressure of the oil?:anyone:

Never, ever pull a vac. on synthetic oil below 500 microns, so I was told. It will boil the oil and it would be (much worse if heater was on). So now you have basically got some oil thats prob. broke down-burnt up,(not that it was exposed to high temp.) but it was exposed to low vac. and normal temp. The oil does'nt know the difference. Pull a vac. on a beaker of water, it will boil at room temp. and even lower because it does'nt know the difference either.

[amickracing]

I've heard 250 microns was the magic number. I kinda don't believe it too much though.

1st off, there's refrigerant in the oil, that's a given, it takes up space, so when you pulled it out, some of that volume was removed. There's also a chance some of it followed the refrigerant out (they bond pretty good together).

[klove]

I go with amick. You depleted the refrigerant that was in solution and lost some level. I don't personally leave the heaters on during evac. Run 'em to heat things up and drive out n/c's but once it goes below about 25", I turm 'em off and let it cool down. I think it's safe to say that you didn't boil that much free oil out of the machine with a vacuum pump - that would take a month of Sundays. (Unless you evaced for that long.) The easy way to tell this is: did your pump oil level rise?

perk: Where'd that piece of info about no vacuum below 500 microns on synthetic oil come from? Never heard that before. Be interesting to hear the in-depth reasoning behind it. I'm assuming this is not synthetic in this machine, anyway, unless someone converted the oil charge.

[amickracing]

I could sum up 4 pages of reading, but it's actually some good reading in there...

http://hvac-talk.com/vbb/showthread.php?t=185533&highlight=boiling

[chilbrig]

The oil in a DK would be mineral oil. A DK has an upper and lower oil sump, and only the upper one has an oil heater. When you pulled the vacuum you boiled the refrigerant out of the oil in the lower sump and the oil level dropped.

[cperk]

original post by klove:::::::perk: Where'd that piece of info about no vacuum below 500 microns on synthetic oil come from? Never heard that before. Be interesting to hear the in-depth reasoning behind it. I'm assuming this is not synthetic in this machine, anyway, unless someone converted the oil charge.[/QUOTE]

I was told by an old Carrier Mech. you prob. know. It may have been 400 mic. I don't have a 19dk, I was assuming it was synthetic. But anytime I have to recover gas to work on a large chiller (min. or syn.) oil, before evacuating I push, or pull the oil out of the system and replace with new, (after I have some pressure above atmosphere). I don't think it's a bad practice, especially if your pulling a deep vac. and don't turn the heaters off. If your that deep in the system why not go ahead and change the oil?