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Old 03-04-2000, 09:19 AM
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I had a $150.00 worth of Freon shot in to my 300 SD W116 122K on a saturday.. Vacuum Pump went out on a Tuesday.. Had the Pump fixed on a Friday and I tried the A/C ..... Nothing, put the gadges on .. No freon at all..
Would the Vacuum Pump problem have anything to do with this, are do a have a problem somewhere else ? The compresser has a lot of oil on the back side.. Any ideas where I should start looking first... I don't wont to waste another $150.00 ..

Thank you , Juan

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Old 03-04-2000, 10:23 AM
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You said that you had freaon added, but what about a system leak check? The original freon had to go somewhere, since this is a closed system. I suspect the $150 dollars worth of freon went the same way as the original charge. The vacuum pump system and A/C are not connected, but it may have been agravated by the vacuum pump work, such as disturbing the lines and increasing the leakage rate, if it is/was a leaking line. Unless you see something really unusual, it is not the fault of the mechanic. Haver you confirmed the electric clutch is engaging when the A/C is selected? Maybe the fuse blew or the electric line to the compressor clutch got knocked off? Also, oil on the back of the compressor is a bad sign! Living in Texas, you will want A/C and I think that you will need a comprehesive fix. Probably, compressor, a line or two, receiver/dryer and freon again. It won't be cheap :-(

87 300TDT
150,000 miles

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Old 03-04-2000, 11:34 PM
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Thank you deezel,I think i will have the A/C system re-done...

[This message has been edited by Webmaster (edited 03-04-2000).]
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Old 03-05-2000, 08:07 PM
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I agree with the information you have received. Should it be that you need a new compressor, and possibly even if you do not, I suggest that you switch from R-12 to R-134. The reason to switch is the cost difference - with R-134 the cost of a recharge is probably $50 or less. The cost of change-over should not be expensive either, when R-134 first came out it was expensive because it was felt that all seals needed to be changed along with the oil & freon. Now many shops simply vacuum the system, add the correct oil for R-134, and add the new freon.

It is extremely important to have a thorough leak test done to the system to find out where the freon is being lost.

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Old 03-06-2000, 07:57 PM
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Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
It is my understanding that systems that use the r-134 generally operate at higher pressures (due to decreased efficiency I guess. I am not aware that it is OK to just dump the r-12 and fill er up with r-134 and drive away. I think you ought to get a well informed opinion about doing that sort of thing.

Jeff L
1987 300e
1989 300e
1987 BMW 325
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Old 03-07-2000, 10:09 PM
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No, you do not "just dump" the R-12. In this case the system was empty so it is a non issue. Also, there really is no reason to convert if there has not been a freon loss. To vac the system the shop would use a recovery unit so the freon would not escape. The R-134 is different in charging the system, it requires weighing the quantity.

There is nothing wrong with R-134 - it cools very well and is used in new cars.

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Old 03-07-2000, 10:25 PM
Join Date: Jan 2000
Location: Indpls.,IN. USA
Posts: 84
Anyone looking to charge an empty system with R-12 these days knows to partial charge and leak test. If your compressor is leaking around the housing it needs a new Delco R4. These are usually reasonably priced. The rule of thumb these days is to convert the system to 134a if a major component is replaced. I think you'll find the performance will be fine.
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Old 03-07-2000, 11:37 PM
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You can get Mercedes' service info for converting R-12 to R-134 from your MB dealer. It is Service Info #83/83 of Oct 1996 (folks cited this last summer here on the Forum). I got a copy free from the parts dept. The service manager told me that MB had found that they got good results without changing very much, but it was important to get out the old lube oil from the ac system.
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Old 03-08-2000, 08:10 AM
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Did you ever find a vacuam pump? If not, contact me again, and we will keep looking until we find one. I have a few other sources I can look up for you if need be.

Also, it seems that posting an R12 vs. R134 topic is getting like getting opinions on oil. All of the posts you've gotten are somewhat helpful, and are all with good intention. But not all of them come from Houston, Texas. There aren't too many large cities that strain an Air Conditioning system, both home and auto, like Houston.

The cooling capacity of R134 is less than that of R12. Also there are two types of oil to be used in an R134 system. PAG is one type and is strictly for systems which have never had R12 in them. Ester is another type and is the only one you can use in converted systems.

There are several downsides to converting, one of which is not a downside for people in climates where they don't deal with a Houston type summer, that downside is the reduced capacity. Theoretically, it is only about a 20% loss. But most a/c's are strained to the absolute edge of operation when in Houston. The 20% loss may be "the straw that breaks the camels back".

Also it seems that the R134 dries out the oil. Benzmac says it should be pumped down, oil changed and recharged every two years.

In spite of these downsides, I totally understand your dillema. R12 is RIDICULOUSLY expensive. I guess I shouldn't get started, but I think that when our govenment voted on banning R12, they should have all been required to live for a full summer in Houston before voting.

juan, I have converted a few vehicles to R134, one of them being a Benz, and I don't know what to tell you. I have been disappointed with the conversions, but losing $150 worth of R12 while troubleshooting a leak is a tough thing to do. It might be worth finding a GOOD independent auto air shop, handing it over to them and letting them find and repair the leak.

I think that this is probably a tough thing for you to do. It is very tough for me to do. I do all my own work, and not only is it difficult to cough up the money for this, but I'm almost admitting defeat when I do it. But I think that if you can find the right shop to find and fix the leak, you will be money ahead in the long run.

Best of luck and let me know if you still need a vac pump,

Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in
Mercedes automobiles
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Old 03-08-2000, 08:02 PM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
Posts: 521
There are many web sites which provide info regarding A/C conversion. Learn more about it before you start. Here is one of them:

I went to one other web site (forget where) which had one page info about older MB conversion. As Chrisg above said, there is not much to change on a MB. I recalled that a new higher rated pressure switch was recommended by the author. He also stated that the conversion on older MBs were not as good as other conversion due to MB's poor design of the A/C system.

If you need a vaccuum pump (not the engine vaccuum pump on a diesel engine) to service your A/C system, you may conver a good compressor from a discarded refrigerator (that was what I used in the shop back in the old days before all the new laws came up). Some compressors work very well as a vaccuum pump.

You A/C system went empty within few days. You had a big leak and it should be very easy to find. You saw a lot of oil on the back side of the compressor. That might be the leaking area.


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