If you convert the A/C on a W126, do the flush, the whole thing - do you need a new pressure switch and/or temperature switch?

I found many of the parts now to be both R12/R134a. I had a "professional" conversion done. He did the receiver/dehydrator (obvious), flushed the system (o.k., one step above obvious, but the most important, and he did it), did not do the rest of the o rings (I ended up doing them with the generous help of CTaylor of this board at his home garage), but it seems now he also did not do the switches.

I know this is a controversial topic. Whenever I order a part, though, I am told it works for both refrigerants. This includes the receiver/dehydrator and the expansion valve. Anyone with experience on the late model 126 want to chime in?

Thanks!

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Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)

First of all it is a real bummer that it has been converted.

After doing atleast a thousand of them, I can guarantee reduced performance and shortened life. The refrigerant charge is about the cheapest coponent in the system, and getting cheaper. Just isn't any reason to change anymore.

Anyway, the switch that you must get is the stock switch from about 83 on. The problem is the original earlier switch looks exactly the same and is cheaper and is widely substituted for the current part. the switch was originally just a low pressure switch designed to shut the system off when the refrigerant charge was real (I mean real) low. The later version of the switch shuts the compressor off if the pressure goes too high as in when the aux fan doesn't work. The hi pressure cut-out keeps the system from popping a cork somewhere at tremendous pressure.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Stevebfl,

On "shortened life", you mean the compressor?

Since this is an '89, would the "stock" switch on it be the right one? I.e. if the switch was never changed, would I have the right switch installed?

I hear all these different things about the pros and cons of converting. It's like the oil thread here - I did a lot of reading, and it seems that there are various opinions on it. I for one like the fact that with R134a I can actually work on the system myself. Bought the gauges, did the expansion valve myself, vacuumed the system, and filled her up. You need a license to do that with R12, not to mention the environmental issues (my fiancee is an attorney at EPA). But I am also aware that the system will not be as efficient as R12.

Thanks for responding.

__________________
Henry Bofinger
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)