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Old 11-18-2002, 09:48 PM
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Join Date: Nov 2002
Location: Orange County, CA
Posts: 95
Unhappy R12 or R134

I am bringing in my car this week to see if my evaporator needs replacing (1987 300D). The parts guy at the dealer said that if I need a new evaporator, to convert to R134 from R12.

What are the pros and cons of each?

1987 300D (176,000 mi)
2001 CLK 430 (18,000 mi)
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Old 11-18-2002, 10:11 PM
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Join Date: Feb 2002
Location: Virginia
Posts: 550
First thing that I'd suggest is doing a search. Use R12 and conversion as keywords, and you'll have a wealth of informed opinions to help you. The bottom line I think, is that R12 is what your system originally was designed for, and will work better in your system than R134. The newer R134 systems are designed with larger condensers that compensate for R134's less efficient cooling ability. R12 is still readily available to your shop, and although R134 is cheaper, enough R12 to fill your system can be had for less than $100 - less than the cost of a proper conversion.

Having said all that, if you want to convert, it's certainly a good time when a major component is being replaced.

82 300 SD
77 450 SL (gone)
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Old 11-18-2002, 10:57 PM
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Join Date: Mar 2000
Posts: 517
Use R-12.

Your '87 300 D will never cool as well with R-134a, unless you perform additional modifications.

Also, ND compressors generally last about 150K miles. If the vehicle is still using its original compressor, you'll want to seriously consider renewing it at this point, esp. if the system has been run for a period of time without a full oil charge or if you wish to switch refrigerants. R-134a runs at a substantially higher discharge pressure than R-12 and this will stress a worn compressor.
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Old 11-18-2002, 11:08 PM
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Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
If you do an evaporator replacement, the refrigerant will be the LEAST expensive part of the bill. Stick with R12. Due to "Black Forest" condensor design and size, our cars don't make close friendships with R134a. The hygroscopic nature of the oils (PAG or ester) for 134a makes acid production more likely and evap. life much shorter. I stopped arguing the efficiency issue long ago ( too many non-scientific opinions), but I will expound the acid issue. I hope it's just an "O" ring gone bad, though, and not the evap.
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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Old 11-19-2002, 09:58 AM
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Join Date: Jul 2001
Posts: 613
I have switched all my cars from R12 to R134 without any problems, although the R134 does not get as cold, with recirc on it gets down to 48 degrees, plenty cold for Seattle summers. My 190 was done two years ago with no issues. One thing to remember is to charge your system to 80% capacity. Of course when I did this switch, I replaced my evap unit, ac filter, condenser and all the O rings. By the time I was finished there was little if no R12 oil left in the system, the only thing original is the compressor.
1993 500E
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Old 11-19-2002, 11:19 AM
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Join Date: May 2002
Location: Mass
Posts: 1,127
Suggest R-12.
Price has fallen dramatically in recent years.
Makes the economics of a conversion less compelling.
Reports on the lifespan of AC components post-conversion are not encouraging. Plus, less cooling.
1986 300E 5-Speed 240k mi.
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Old 11-21-2002, 07:41 AM
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I went through the phase of converting every car in site. Since that time, I have begun "reverse converting." That is going BACK to R12. If the car was not originally designed as an r134 system, it will just not be right. When doing a significant a/c repair, R12 is almost always the least expensive purchase of the project.

Good luck in your decision,
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