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R-12 to R-134 A/C Conversion (Long)
Audi has a Technical Service Bulletin (TSB) on this subject. I have that
TSB in an electronic form which requires proprietary software from "efax" to
read. "Efax" are the people who provide a free fax number. If you want to
go to their site and download their software, I will send it to you. Or,
maybe someone else can send it to you in another form.
The TSB wants you to change some seals in the compressor; replace the
dryer; flush the system with solvent; change the ports; change the oil; and
maybe do some other things I forgot here. With the exception of the seals
on the compressor and the amount of oil to put in the system, the TSB's
instructions are the same as any other instructions on converting.
Most of the mechanically inclined people I have heard from on this subject
are not very fussy about the conversion. They just open the system up to
vent it of R-12 (This is illegal.) and to drain some old oil; throw in an
amount of R-134 compatible oil; and charge with 3 cans of R-134. The amount
of R-134 should be about 15% less than the amount of R-12 specified for your
You can fool around like this with R-134 because the cans are only $5 each.
The cans of R-12 are $40+ each when and if you can find them. You will also
need to buy a conversion kit which contains different sized (for R-134)
ports. That kit is ~$35. Your local automotive parts store will have all
the stuff you need to do this conversion.
Of course, you will need to fix any leaks and faulty components of the A/C
system no matter which refrigerant you use. Most people report a slight
decrease in cooling after this conversion.
In the old days, it was considered ordinary maintenance to recharge your
R-12 system regularly. R-12 was cheap. Just throw a $5 can in once in a
while. R-12 is now considered to be bad for the environment and is being
phased out. You can still get it. But it is difficult and expensive and
getting more so every year. So far, R-134 is the replacement refrigerant of
When R-134 was first proposed, it was thought that R-12 A/C systems would
need extensive changes in order to work with the R-134. It was thought that
the R-134 leaked easier so seals and hoses would need upgrading. The oils
used with these 2 refrigerants are not compatible. Therefore, it was
thought that it was necessary to get every little drop of the old oil out.
Where the A/C system is being opened to the atmosphere, it is always a good
idea to replace the dryer. As you can see, all this would be very
Experience is now showing that if the R-134 is indeed "leakier", it is cheap
enough to keep replenished. R-134 is not compatible with R-12 oil, but it
seems that a little R-12 oil won't hurt as long as there is enough R-134 oil
in the system. Maybe you should replace seals, hoses, the dryer, and
retrofit the compressor for optimal performance. But it appears you can get
adequate cooling without having to do so.
All this assumes you are doing the work yourself. It also assumes that you
do not have access to specialized A/C shop tools and test equipment.