Hello everybody, new here with a question. Been lurking for a while looking for info on this subject but haven't seen what I am going to ask.

Have a '89 Chevy G20 with the R12 of course that is inop. We pulled a vacuum and it held for 30'. Then charged with the R134 and UV enhanced appropriate oil. Well it is below the threshold for the compressor to run now in about a months time and no leakage can be detected with the blue light.

So rather then waste more time and money on an old system that doesn't compare to a better designed R134 system, am thinking of changing to an R134 system, taking the stuff needed off a 94-95 vintage model.

How it would change over is the question. I figure I would need the brackets as the compressors are different, can purchase most of the other parts new at the parts stores, except maybe for the hoses. Maybe the configuration of the alternators and other parts have been moved, I don't know.

So anybody done a comparo of these two to determine the difficulties or ease of the changeover? Thx.

When you pull a vacuum, leave it there for a couple of days with a known good set of gauges. Did you jump out the switch? Check the pressure with good gauges? Remember all the seals have to be compatible with the gas.

Okay, just really added the background info as fyi. Professional mechanic was attending to the conversion and I don't wish to pursue everyone's knowledge base of this.

Really want to know if anyone has done the r12 to r134 equipment conversion.

I did.... had my 92 G30 changed over to R134 ... cost me $700

Marcela, welcome.
A system that does not leak R12 can leak R134 like a sieve....
The molecules that make up R134 are much smaller that the molecules that make up R12. These smaller molecules can slowly escape at (usually multiple) locations in the old systems where the (larger) R12 was secure. These leaks may be too tiny to be easily detected and may hold vacuum just fine. Some of the older hoses can actually allow R134 to slowly seep thru the walls of the hose itself.
The older the system the more of a problem this becomes. Your '89 would be in that category. As the manufacturers came under fire by the EPA for leaky systems they refined their materials so the later R12 systems were somewhat tighter.

Hope this helps with the background leakage info.

BTW your professional AC tech should know all this ......

Changing the system to the later 94/95 system would solve the leakage problem but will not be easy or cheap. The 94/95 is a completely different design. For instance, the new system has a suction accumulator in the low side for excess refrigerant and the older system used a dryer/receiver in the high side. The new system is a orifice metered system and the old system used a thermostatic expansion valve.
Long story short ... the entire system (including compressor) will need to swap.

What I would do to save money and work is have all the hoses remade using modern materials, the compressor upgraded and O-rings/connections replaced with R134 compatible types. The R134 will cool using the older design but it will only be about 70 to 80 percent as effective.
Still it will save major bucks. Have your evaporator and condenser coils pressure tested to be sure they are leak free as well.
My 2%

Interesting Catfish, thanks for the info.

I knew about the hose thing and figure that is where all the molecules went as I haven't detected the leak from the metal parts yet. It was a crap shoot but only cost $140. Just don't want to do it again.

I figure to find a junked van and rob the a/c parts. Had one close by but wasn't ready to commit. Since the body style is the same I believe this should work, if not let me know. Not looking forward to working in the tight quarters.

The van is like new with 83k miles originating in TX then southern KS, old people driven and spent time in a garage or I wouldn't be pursuing this avenue. And I may not get it done but no a/c is not gonna work for me i don't believe.

I'd prefer to have the system designed for the R134 if possible, especially using a more efficient compressor designed for it.

I went through and replaced my 1985's A/C system with all new parts (literally every part). And I'm running R134 through the 1985 spec parts just fine, You just need to make sure to run the correct type of oil, and get the conversion fittings. I wouldn't trust the r134 on original parts however.

Might end up doing that also and replacing the hoses, especially the long ones to the a/c in the back.

I painted myself in the same corner last year. The clutch was making noise so I got a new compressor, after installing it I realized there was no way I could run all the old dirty parts thru my new compressor. The 134 is made to replace 12 the trick is to replace all the seals with ones that work with the gas and flush the system. I did refer work in my 20's around the time 12 got outlawed, on the slower days we would just play with things for fun. We would put the wrong gases in systems just to see if we could make it work. The 134 will work you just have to prep for it.