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Old 09-02-2003, 06:43 PM
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Join Date: Jun 2002
Location: Monrovia, CA
Posts: 490
Question About A/C OIl

Here's a question for the A/C pros/specialists out there. This is on a 1986 300E with the original R12 system:

How can I determine whether the oil in my air conditioning system is at the proper level or not? I replaced the A/C hose assembly, expansion valve and the receiver-drier over the weekend. According to the service CD, I should be replacing 20cc for the hose assembly and 20cc for the receiver drier. However, I wasn't able to drain any more than about 10 drops out of the complete hose/manifold assembly. I haven't tried draining receiver-drier yet, but will try that tonight. And do I just inject the oil into one of the lines or the receiver-drier itself? Or is there one place in the system where the oil tends to collect that can be drained and refilled with a known amount? Is there any danger in overfilling the system?

I want to take the car in tomorrow to have it evacuated and refilled with R12, but I want to make sure there's the right amount of lubricant in it first.

I also noticed a some rust-appearing corrosion inside the condensor pipe where the metal pressure line connects to the LH side of the condensor. Is this anything to worry or do anything about? The rest of the lines appeared clean and corrosion free.

Thanks for any help.

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Old 09-02-2003, 08:27 PM
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Join Date: Aug 2003
Location: northern Calif
Posts: 72
a/c oil

put in the amount that is indicated in the manual, it is hard to over fill the system by using recommended levels, normal small leaks over the years ,leak out refrigerant and will find the most oil in the lowest and coldest part of the a/c system.hope this helps,BILL.

1981 240d 197,000
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Old 09-02-2003, 10:42 PM
Registered User
Join Date: Jun 2002
Location: Monrovia, CA
Posts: 490
Well, I'm concerned with underfilling it too. Seeing as the pump is the lowest part of the system, is there any accurate way to drain and refill it in situ? What's the total capacity in a new system?

Also, what about the corrosion in the condensor connector? Any need to be concerned? It's not throughout the system, but I don't really know how far it goes, only that all the other hose and pipe connections looked clean internally. Is a little bit of corrosion normal over the years and does it tend to stay put?

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Old 09-03-2003, 09:46 AM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,743
Anything short of taking everything apart and flushing the system is a guess at the present oil level. Oil is distributed throughout the system and one can only make an educated guess at how much needs to be replaced during a repair. Overfilling the system will make it less efficient because the refrigerant volume is displaced by the lubricant.
95 E320 Cabriolet, 131K
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