Some things to consider. A quality conversion to R134a can be accomplished but you need some R134a specific components. The condenser is different and the H valve or expansion valve is also different. The addition of an electric fan for the condenser also helps to keep the high side pressure down when sitting in traffic.

I did the conversion on my 92 D250. I used a R134a compatible condenser, a newer R134a H valve, a new compressor, evaporator and drier. Others maintain you need to change the hoses to the newer barrier style but I didn't do that as they are not available. Yeah I know I could have had them made but my hose ends are not in great shape and I didn't want to mess with them. So I flushed the hoses really well and used PAG oil because I work at a dealership and there are plenty of half used cans of the stuff sitting around. I also added two 8" electric pusher fans on the condenser.

Either way it works well, will cycle the compressor if it's not on high at around 38*. In the 5 years since I did the conversion I have not had to add any refrigerant. The biggest problem I have with the old gal is keeping the hot outside air out of the cab. If it wasn't for that this thing would cool awesome.

ok,my 2 cents ,i have a 92 dakota that had a hose go bad ,so i bought a new hose and drier and expansion block,i bought some 134 compatible oil dumped some in by guesswork,didnt drain the old oil at all!,evac and charged with 134,works good,but it had a problem at idle it would push out some gas out of the pop off valve thats screwed in the back of the compressor,so come winter time i removed the valve and filled it with jb weld and put it back in,evac and charged the system,works fine,no leaks,this was at least 5 yrs ago,maybe more,compressor is somewhat noisy but was before i converted it,i was told by a mechanic at the time the compressor wasnt going to last very long?,as it and the truck has 348000 miles on it and still puttin out cold air
your experience may vary!1

Ive a couple cans of R12 I will never use if it would help, although I seen you posted you had some?

Thanks EV2, appreciate the offer.
Will let you know if I need it.

Thanks for all the detailed replies, learning a lot.

Another couple of questions based on above :

How can I tell what type of refrigerant was used to charge the restored system if there were no obvious changes to valves etc?

If 134a was used and can be replaced with R12, would a shop need a 134a machine to remove the 134a or can it be removed with any machine?

Would it need to be somehow "flushed out" of all previous contents before recharging with R12?

If the charge ports haven't been changed then it probably has R12 in the system but the only way to know for sure would be to have an A/C shop with a tester identify the refrigerant.

If it has 134A in the system, legally it would need to be removed with a 134A recycling machine.

Flushing the system would be required to remove the PAG oil if going from 134A back to R12 and wouldn't be a bad idea even if the system has R12 in it. I would replace the dryer also.

I prefer to use R12 in my old cars, fortunately I still have some left. I would suggest sticking with R12 if you have access to it.

Thanks for the reply Ply72rr.

The charging ports don't appear to be changed, but I was just told that 134a was used. So not sure what's in there, that's why I am hoping a shop can identify and then take action based on what's there.

Appreciate all the replies.
Will let you know what I find out...

If it has R134a in it I would keep it. It's far easier to deal with and readily available. The problem with R12 is that there aren't many shops with the equipment to deal with it. You can't recover R12 with a R134a machine as has been stated previously. You end up with a contaminated machine and tank.

is it possible to put in R134 without changing the port fittings ?

Anything is possible.

Like putting on the fittings, filling it up with R134 and removing the fittings.

Yeah, they are supposed to be non-removeable, they aren't.

you are correct, anything is possible. i wondered about this because the adapters i have used in the past, boogered up the fitting threads, supposedly making the 134 conversion "permanent". but you "had" to install the little sticker included with the conversion kit to make "sure" the conversion was complete !

I still have an unopened 30LB cyl.of R12.

Okay so according to Classic Air the original components ( compressor, clutch, filter drier and hoses ) were rebuilt to be compatible for BOTH R134a and R12.

The resto shop said they used 134a to charge system (but see no difference in the charging valves/ports).

If I wanted to go back to R12 then Classic Air would have to re-restore compressor and drier at the least...

Don't know of anyone that has a sniffer to detect R12 vs R134a.
Any obvious ways to tell to confirm?

This is likely what they did if they charged it with R134a

Why? If the components were "rebuilt to be compatible for BOTH R134a and R12" a simple change in refrigerant shouldn't be a problem.

Most current driers are compatible with both refrigerants, as is ester oil, so you can swap back and forth as desired.

Good point John.
Why can't I simply replace 134a with R12 .

I'm waiting to hear back from Classic Air to confirm.

What about the oil , per above reply each refrigerant uses a different oil , won't that require some work to flush the R134a oil out ?

"R12 uses mineral oil R134 uses ester or PAG oil."

I assume that, if it was configured to use both refrigerants, it has ester oil which is compatible with both.

Hay MONC just noticed u live up here in the HV so I guess you have the green 72 with the air grabber I've seen running around here,I have all the tools to service your a/c.

just if somebody is interested... old article but I think still valid

When doing an R134a conversion, should a guy be adding a high pressure cutout switch and/or a pressure relief valve? I don't know about adding the valve but high pressure switch doesn't look like it would be too tough to add.

Heard back from Classic Air and they said regarding evacuating R134a to put in R12 "As long as you flush the system it can be done"

So we'll see.


Thanks for posting NachoRT