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Old 07-20-2000, 11:29 PM
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Join Date: Mar 2000
Posts: 532
A friend recently complained of poor A/C cooling in his '93 190E 2.3. Inspection reveals a low freon charge but more importantly, across the R-12 refrigerant capacity sticker is written "134a - 24 oz"
[stated system capacity is 2.2 lbs]. The freon charge fittings are standard R-12.

Freon analysis reveals the presence of an R-12/R134 blend. The composition of the refrigerant oil is unknown.

He is the original owner and states that the only prior A/C work was approx. a year ago; he was unaware of this "pseudo-conversion".

Assuming no compressor damage, will replacement of the leaking component(s) and the receiver/drier be sufficient or should the system also be aggressively flushed? Any technical insight would be appreciated. TIA.

[This message has been edited by jgl1 (edited 07-20-2000).]
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Old 07-21-2000, 09:52 AM
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This was a JakeLeg job of conversion, but I'm sure you already know that.

R12 and R134 are so incompatible that this caused the change in fittings and guage sets. I've been told to never get the two near each other.

First of all, the quantity should not be too far off, but a little low. According to Benzmac, and I have seen this work out pretty well a few times in practice, you should charge with 75 to 80% of the specified volume when changing to 134. In this system, 2.2 pounds would be about 35 ounces, 75% would, of course, be about 26 or 27 ounces. I believe that as a bare minimum, this system should be emptied, and the oil changed to Ester. It would be better to break connections and flush aggressively as you put it. If you do this, change to the green O-rings, put in the Ester and pump it down. Whenever you have the time to do so, it's very good if you can pump down for 24 hours. In any automotive A/C, R12 or R134, any moisture in the system combines with the refrigerant to produce an acid which can eat up evaporators and other components from the inside out. R134 is much more prone to developing this acid when combined with moisture left in the system. This is why I always try to pump down a system which has been broken apart, for 24 hours where practical.

Good luck,

Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

[This message has been edited by LarryBible (edited 07-21-2000).]
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Old 07-21-2000, 10:00 AM
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Join Date: Jun 2000
Location: Baton Rouge, LA.
Posts: 583
First you need to find out which refridgerant it's supposed to use. When the industry began it's conversion to R134A in all the training classes I attended it was preached that you do not mix R12 & R134A ever!! The compressor oil's, hoses and just about everything that was not metal was not compatible. So my suggestion is that when you tear down the system you need to do a complete system flush. Then you can do one of two thing's. First you can go back with R12 if that is was originally used or you can convert to R134A, which could possibly reguire some hose changes and oring replacement. Either way you should not have both in your system.

Keith Schuster
83 300D
auto\hydraulic mechanic 20 yrs
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