Hopefully someone with more expertise wil post, but certainly the two
are not compatible as they act under different pressures.

For my 2 cents I think your friend has been lucky. Lets face it, how
does someone determine their air conditioner needs help - when it's
not cooling, usually at all. How many people do you know that say "I
put a thermometer up to my a/c outlet and the air is 3 degrees warmer
than it should be". Usually it's not blowing cold - e.g. out of R12.
I have successfuly recharged empty R12 systems with R134 without
replacing any parts. It is kind of silly, since I still don't
determine what is wrong, but it's not in my daily driver so I don't
worry. In addition it is not as efficient as swapping out the
appropriate parts (and leaking ones...), but it will work at least
decently. It has to be "under charged" as I believe you only use
about 80 percent as much R134 pressure as you would R12. Even if you
don't have the proper manifolds for measuring all of that the kits
come with a small guage that does the trick.

Bottom line is you would not properly recharge a system if you don't
create a vacuum in the system first, and if you create a vacuum I
believe you would have evaculated all of the R12.

Finally, the oil used in R12 is not compatable with R134 so the system
will fail sooner rather than later, if you don't evacuate that R12 oil
and put in the proper oil.


On Sun, 28 May 2006 17:12:54 -0500, (m Ransley)
wrote:

A friend has been filling R12 systems on cars with R134a and says
there is no need to evacuate out R12, he has done it for years on many
cars. Is he lucky to not of had his friends cars damaged or can I just
put in R134a in my R12 system without evacuating out R12.