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1988 300CE
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Discussion Starter #1
I have just put in a new (rebuilt) AC compressor in my '88 300CE. The coolant has been 134a for a time based on the fittings. Is there some type of lubricant for the compressor other than the lubricant in the 134a and the lubricant in the compressor when it came from the rebuilder?
 

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CH4S Admin , Outstanding Contributor
1985 500SEC, 1991 190E 2.6.
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39,643 Posts
I have just put in a new (rebuilt) AC compressor in my '88 300CE. The coolant has been 134a for a time based on the fittings. Is there some type of lubricant for the compressor other than the lubricant in the 134a and the lubricant in the compressor when it came from the rebuilder?
Welcome. I moved your post to the correct W124 forum.
All I know is that the lubricants for R12 and R134 are different, and available in measured quantities (small cans), and added to the freon from the low pressure side.
Did the rebuilder or you evacuate the system with a good vacuum pump, to remove all content and moisture, and see how long the system holds vacuum?
I don't know about the W124, but the W126 forum has a 'Welcome .....' sticky to show how to run a forum search. The archive has multiple threads re this topic.
Cheers
 

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Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
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5,454 Posts
I may have some bad news, Dave. A new or rebuilt compressor typically comes with a lot more oil inside than is required. After opening the box, you should uncap and tip the compressor to drain out all the oil that you can. You discard that oil. Then you estimate the amount of oil that the system should require and you add that amount of NEW oil.
Figuring out how much oil to add is not an exact science and the most angst-inspiring part of an a/c repair (for me anyway). If there was a catastrophic failure like a collision where all the refrigerant was dumped in a few seconds you usually add a full oil charge (as indicated on the underhood label). If you had a leaking hose that gradually vented the charge and left little oil staining, I usually add 2 oz. If the leak area is an oily mess I add another 2 or 3 oz. Too much oil is bad because it reduces cooling capacity. Way too much oil will hydrolock the compressor. Too little oil will cause the compressor to wear out prematurely. Sucks, huh?
The only 100% sure way to get exactly the right amount of oil is to remove each component and drain the oil out of it. Way impractical for the evaporator.
You can get close by draining the receiver-drier, the place where a lot of oil pools (other than the compressor).
 

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1988 300CE
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6 Posts
Discussion Starter #4
Compressor Oil

I replaced the drier so it is new but I did not intentionally empty the compressor other than what spilled along the way. The rebuilders instructions said not to remove their oil but to fill to specification (which I find no place) for my car. I am going to Grainger to pick up my vacuum unit today.
 
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