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Old 07-23-2002, 12:25 PM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
R12 to 134 Conversion on 300D 85

First of all, does anyone know where I can buy a vacuum pump used? Is there a way I can make one?

How do I get the PAG oil in safely? The last time, I took the compressor off, flushed it, and poured the oil in.

Some people say all I have to do is use one of those conversion kits but I would rather do it thoroughly and correctly.
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Old 07-23-2002, 12:50 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,804
It's good to hear you're doing it properly.

As far as vacuum pumps, I've made some from discarded refrigerator and dehumidifier compressors. Once the unit is removed from the refrigerator, use the suction line to pull a vacuum. Works well enough. New one can be bought from the internet for roughly $250. (Still a savings for the do-it-yourselfer, compared with having this job done for you.) Try or for more information.

A/C compressors, per se, don't get flushed during a conversion like the other parts. You simply drain as much oil as possible, turning the shaft a few times during draining. Then run some new PAG oil through the compressor to wash out the old oil. All other passages, with the exception of receiver/drier, orifice valve, and any filters, get flushed with solvent.

To charge the system with oil, put half the required amount in the compressor, and distribute the rest throughout the system. That way, the a/c system wont be starved for oil during startup.
95 E320 Cabriolet, 140K
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Old 07-23-2002, 01:55 PM
Posts: n/a
I used an old refrigerator compressor for years, it finally laid down and I found a wet vane Robinaire pump for $100 in like new condition. I felt that it was a bargain. The refrigerator compressor would pull about 25 or 26 inches, good enough. There is a write up at about how to make a fancy pump out of one.

I would not flush the compressor, simply pour out all the oil you can get out of it. Additionally if you are going to use PAG, you really need to flush EVERYTHING. It is not as compatible with residual mineral oil as is Ester. If you will flush all lines, the condensor, the evaporator and replace the filter drier, PAG should work good, especially with your R4 compressor.

If you really want to be thorough and do a good job, get the brass conversion fittings rather than the aluminum ones from AutoZone. Also replace all the o-rings with the r134 compatible ones and use the Nylog lubricant on them.

I don't know exactly which kits you're talking about. If you're talking about the one with the single hose and some r134, these are called "death kits" at This does not mean death of the operator, but death to the air conditioner. If you are talking about the retrofit kits with Ester oil, fittings and a few o-rings they are okay. They, however, usually have the aluminum adapter fittings rather than the good ones. The brass fittings are available from for about $3 each.

Also, Carrameow, be careful with the manifold on the back of the R4 compressor. Loosen the bracket on the line that clamps it at the upper part of the compressor mounting. Get the lines loose, so that you can start the center manifold bolt in straight. Once you have it in place and tight, THEN tighten the line brackets in place.

Once everything is flushed make sure you get the correct amount of oil in place and pump it down well. r134 is more susceptible to combining with moisture to make acid than is r12.

Good luck,

Last edited by LarryBible; 07-23-2002 at 02:05 PM.
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Old 07-25-2002, 12:57 PM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
Thank you very much for taking the time...

Dear Larry
Please see this EBAY convinced me. Do you think its a good deal? I am 41 now, i guess I have at least 5 or 6 charges ahead of me, the only thing tht actually might limit you and me from working on cars is the chips/digital long as thier are Mercedes diesels up to 90...........

Hope the IT world is doing okay.Best regards
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Old 07-25-2002, 02:22 PM
Posts: n/a

I don't even plan on the computer engine/chassis management to keep me from it. I bought a system that I run on my laptop that lets me draw codes even from my C Class. The air conditioners I will always expect to be servicable by a competent a/c do it yourselfer.

I'm just trying to keep up.

Have a great day,
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