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Old 07-30-2002, 11:39 AM
Michael B
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Easy, But Stupid AC Question

I'm replacing the compressor and dryer on my 260e. Do I have to fill the compressor with oil before driving to the shop and getting the system evacuated? I won't be running the a/c during the drive... but must there be oil in it? I purchased a rebuilt unit with a new clutch.

Also, what kind of oil? How is it introduced to the system?

Michael B
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Old 07-30-2002, 12:01 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,741
First, you need to know what refrigerant will be used in the system....r12 or r134. This will determine what oil you'll use. Are you doing a conversion from r12 to r134 at this time?....if so, you need to flush the system....r12 oil will be a problem in a r134 system.

How much oil to put in depends on how much was lost. Without flushing all the plumbing, it's only a guess how much needs to go in. Assuming the compressor you got was sold without any oil, a compressor change requires replacement of approximately half the specified oil charge (you'll need to find the specs). It can be poured directly into the system before closing it up (recommended), or charged from pressurized cans after it is closed up.

You didn't mention anything about the dryer/accumulator. This should probably be changed along with the compressor. Moisture in the system will eventually form acids that shorten the life of your a/c system.

Did your old compressor break up internally, sending debris through the system? If this happened, you need to flush out the debris from all the components or the new compressor will fail in short order.
95 E320 Cabriolet, 131K
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Old 07-30-2002, 01:09 PM
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Kestas offered a very good and accurate reply. I only want to stress how important it is to flush the system, followed by flushing the system, then follow up by flushing the system. On top of that operation it would be good to use a suction side filter that you can get from your auto ac parts supply.

If you are changing to r134, the flushing will remove all the mineral oil and make way for PAG or Ester. If you do not flush (did I mention that if you had a failed ocmpressor you should flush?) and are changing to 134, Ester will work better. If this is a Nippondenso compressor, PAG 46 is preferrable, but ONLY if you have thoroughly flushed the old oil out. Replacing the filter drier should be considered absolutely mandatory with the system being opened AND a new compressor installed.

This is not an accumulator system, this means that the filter drier is after the condensor and before the evaporator. If you had a failed compressor there will be lots of junk in the evaporator with no filter between it and the compressor. Without thorough flush and suction side filter, chance of compressor failure is high.

Good luck,
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