Another Insult

No sooner have I retrieved my 300D from the engine shop with completely new everything, EXCEPT, I did not replace the A/C Compressor, but did have it switched to the new R134A refrigerant.
Well, today, I was motoring down the freeway, when smoke began to plume from behind, and POOF. A/C compressor seized!. The engine quit, of course, and I had the car towed to the shop.
We'll see how much this will cost, for a new compressor and the labor to install, etc.
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wrote:

I hope you had it towed to a shop other than the one that keeps screwing everything up, ie all the problems you had after the engine rebuild and how long it took them to figure it out. It's suspicious the compressor failed right after the conversion.
I would have taken it someplace else where you could have gotten an independent evaluation and might have found out they screwed that up too by doing something like not putting oil in it, or not evacuating and correctly refilling it, etc. If you took it back to the screw ups, all they are gonna tell you is you need a new compressor because it just went kaput on it's own and you're gonna pay for the whole thing anyway.
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On Sep 19, 4:35am, snipped-for-privacy@optonline.net wrote:

Your points are well taken, and bring up a question: What exactly does cause a compressor to fail? You mentioned not properly evacuating it, and oil.
I do know that the shop had to recharge the system several times, and never seemed to get it to work properly after converting from R12 to R134 refrigerant. Last week, when I picked the car up from the shop, the mechanic said the air conditioning worked. It "worked" only to the extent that the fan activated and blew air, but the air output was the temperature of dog's breath. It has never "worked" like you would expect an air conditioner to work, i.e., blowing cold air.
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Definitely time to change the shop. AC is not that difficult to work on if the mechanic has the proper tools.
Possible causes of compressor seizure: 1. not enough oil 2. incorrect type of oil 3. debris
R12 uses mineral oil while R134a uses ester or PAG. R134a has different characteristic and cannot circulate mineral oil. Without adequate lubrication, the compressor will grind to a halt quickly. Sometimes the failing compressor creates debris and kills itself. Debris can also be introduced by opening the system without proper capping (for example, during the engine replacement).
AC does not need to be opened (even for a conversion) unless a component in its system is replaced. Now it needs to be opened to replace the compressor. The receiver/drier should be replaced every time the system is open. Existing oil should be drained as much as possible, especially there was mineral oil in the past. The mineral oil itself will not hurt the new system but it takes up volume while does not do any cooling. Flush the system as much as possible. Connect all components then evacuate with a vacuum pump for at least 30 minutes. Finally charge it with correct amount of R134a and lubricant. The optimum R134a is about 85% of the volume of R12.
Remember that your AC system was designed for R12. R134a needs slightly larger system to perform as good. Therefore, the cooling will never be the same as new. However, my two conversions (84 190D and 87 300SDL) work pretty well for me (in mid-Atlantic area, not the Arizona desert :-).
randallbrink wrote:

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Thanks very much for this information and for th thorough description of the system works. I am planning now to restore the system to R12, given that the compressor and components will need replacement anyway.
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Siezed AC compressor is almost always lack of oil... when you vacuum out the refrigerant, you also take out the oil... With a fairly new machine, you would know exactly how much oil you took out and reinject the same amount.
So whoever last worked on it, didn't make sure you have neough oil. Get cheap compressor on ebay and have someone put it in... Don't let the shop take you for a ride on the compressor... On youe car, it is probably about $100 for a rebuilt compressor on ebay. I buy ebay compressor all the time... zero problem.
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http://cgi.ebay.com/ebaymotors/1977-1985-Mercedes-300D-300SD-300TD-280-A-C-COMPRESSOR_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem48374ca439QQitemZ310165414969QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
I have bought two MB compressors from him.with optional drier... cheap too.
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Tiger, Thanks. I'll pursue this, as I am now going to restore the system to R12. I shold never have let the mechanic talk me into converting to 134 in the first place.
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