Top Post......
There are pag oils out there which are compatible with both freons...
Did a few on the side (out side of my shop)
And never had any problems...
Steve
Re: converting from R12 to R134  

Group: alt.autos.chevrolet.malibu Date: Thu, Jul 7, 2005, 3:04pm (CDT+5)
From: henri_latour@hotmail.com (Henri)
I have some antique cars and when I looked into R12 conversions I was
told that there are 3 kinds of conversion.
They first check to make sure the system is working OK.Any hoses or
components that are damaged must be replaced.
1st one is called a dirty conversion.The system is evacuated and a flush
is done to get most of the old R12 oil out of the system.The seals are
replaced and the system is recharged with R134..
The second kind is called a partial conversion. The system is evacuated
and a flush is done to get most of the old R12 oil out of the system.
The Accumulator/drier is replaced, the seals are replaced and the system
is recharged with R134.
The 3 kind is a full conversion where everything but the evaporator and
condenser are changed out.
The most common appears to be the dirty conversion or the partial
conversion and I am told the partial conversion runs around $250cdn. The
only problem with the dirty conversion is that if all the old R12 oil is
NOT removed from the system, the A/C system can gum up when the R134 oil
is added.
There are products now on the market which are compatible with R12 and
can be added to the old R12 without conversion. I am looking at Duracool
to do a drop in replacement for the old R12.
http://www.duracool.com/Duracool/purchase.html or
Red Tek http://63.135.115.175/ 
Hope this helps.
"Plantagenet_Palliser" <lasalle1@pacbell.net> wrote in message
news:1pcqc11q6iusq578kc18ct1eocoi5tqi44@4ax.com... I have an 87 Monte
Carlo w/R12 coolant. Anyone knows what's involved in changing out to
R134?
I'm told that the hoses have to be changed out and system flushed.
Anyone know if there is some factory pub. telling you how to do it?
TIA

So what's your point. The fellow might not have been on e-mail a million
times ago. Did you think of before becoming obtuse.

the topic has been covered over 1,000,000 times

Well, I'll make it the One millionth + 1.

I went back to the dealership I bought the car from here in Glendale,
California.

They had to change out nearly everything.  Took about a day and a
half.

Cost:  $1200.00

Interestingly the AC mech who did the work owned an identical  Monte.

The R134 seems to cool about as effectively as the R12.  I'm told the
R12 is not being used  in California any more.