Will external vac. pump for AC system vac oil out?? - PeachParts Mercedes-Benz Forum

JimmyL · #1 03-02-2009, 12:30 AM

I've spent the weekend redoing the AC system on Smash. I will add details to my cheap wagon thread, but had a question.
After replacing all the parts and the o'rings and adding the ester oil, I attached the evacuation pump to my AC gauge lines.
So, can this suck out some of the oil that is installed in the system? I had pretty much the exact amount I needed and hope none is removed via the vacuuming......

mytmousemalibu · #2 03-02-2009, 01:05 AM

Quote:

Originally Posted by JimmyL

I've spent the weekend redoing the AC system on Smash. I will add details to my cheap wagon thread, but had a question.
After replacing all the parts and the o'rings and adding the ester oil, I attached the evacuation pump to my AC gauge lines.
So, can this suck out some of the oil that is installed in the system? I had pretty much the exact amount I needed and hope none is removed via the vacuuming......

Speaking in generalitys, depends on the car and A/C service equipment. Does your vac pump have an oil collection resivior? If so you can see how much it draws ou and inject that much back, if not, it likly is vented to atmoshere, you will likly see any suctioned oil discharged out the pump exhaust. If you can, recover that oil to see how much to add back. Its prolly not goin to do any harm to add a touch extra oil. Is this a retrofit to R-134a or R-12 refill? R-134a needs PAG oil as refill and at our shop doing a retrofit, we repalace the o-rings, reciver/dryer, flush the condenser with a/c flush and purge with air to remove flush. Also replace clean any screens, possibly replace the expansion valve, and remove as much oil from the a/c compressor as possible and refill with PAG. Hope that helps!

Cr from Texas · #3 03-02-2009, 01:26 AM

Jimmy,
How did you add the oil?
Directly to the compressor and drier as recommended or into the lines?
I'm starting a rebuild on mine and I'd be interested in some more details.

R-12 or 134a?

I found a synthetic oil rated for use with either that I plan to use. I have about 15 lbs of R-12 and when that's gone, I'll convert. I'm thinking I won't have to worry about oil compatability that way.

JimmyL · #4 03-02-2009, 01:50 AM

R12 or R134a?? Neither. Freeze12, hence the ester oil.
I flushed evap and condenser [they were very clean], replaced rec/dryer and exp. valve. The expansion valve was my leak source as I saw the oil bubbling out the side after I charged it upon first purchasing the car.
There was a very cracked and hardened o-ring off the larger of the two condenser fittings, so that might have been leaking also.
Compressor was already a fairly new Delco my neighbor had installed. I did NOT remove the manifold lines at the compressor, but busted them open most other places and replace and nylog'd o-rings.
I added half the oil in the new rec/dryer and half down the low pressure hose prior to compressor, right at the fitting by the top low side schrader fitting. I've done it that way a couple of times before. I always spin the compressor first for multiple revolutions so it doesn't slug.
Works for the non-professional.
The vac held for over an hour, so I installed one can of refrigerant and that pressure has held exactly for 3 hours now. We'll hope it is the same in the morning.......

daw_two · #5 03-02-2009, 10:03 AM

Well, did you check it before you went to work? Did it hold overnight?

JimmyL · #6 03-02-2009, 12:32 PM

Nope. My gauge hoses r awful though. will hook back up tonight. lost 4 on low side

tangofox007 · #7 03-02-2009, 12:41 PM

Quote:

Originally Posted by JimmyL

Nope. My gauge hoses r awful though. will hook back up tonight. lost 4 on low side

Static pressures are highly dependent on ambient temperature.

Cr from Texas · #8 03-02-2009, 01:26 PM

Quote:

Originally Posted by tangofox007

Static pressures are highly dependent on ambient temperature.

And I got down below freezing last night in DFW, right?

Others strongly recommend pressure testing with nitrogen. I guess as a DIY, you skipped that and just did the vacuum test. I would think oil added to the lines would be the most likely to be vacuum out by the pump.

Matt L · #9 03-02-2009, 01:39 PM

The oil won't come out unless it is carried out by liquid refrigerant. That can happen during recovery, but not during evacuation.

It is very hard to determine if you have a leak by looking at the refrigerant pressure. If there is any liquid at all in the system, the quantity of refrigerant has no bearing whatsoever on the pressure. That is why nitrogen is used, as it will not condense to a liquid in the system.

compu_85 · #10 03-02-2009, 01:52 PM

Ya, compared to how quickly a leak causes the pressure in the system to rush out, the vac pump (at least mine anyway) moves things much more slowly. I can't see it pulling any oil out, especially because the ports are up high.

-Jason