Mixing R134A with R12

Will a 12oz can or less “marry-up” R12 in a R12 system. (92 Jeep 4.0)

You cannot mix R-12 with R-134a, they are not compatible (and neither are the compressor oils used with them). If you have a R-12 system, you either need to use R-12 (make sure you fix the leak first, it’s currently selling for about $60/pound), or “convert” the system to R-134a (including having it flushed and evacuated).

There are some other products out there (freeze 12, etc) that claim to be compatible with R-12 for a lower cost, proceed at your own risk.

The fittings for the two freon systems are not compatible . That should tell you something !

No, don’t do this. It might work for a while, but eventually you will have to get the system fixed. There is some sort of leak or you would not need to add freon, so even if it’s slow now eventually it will get bad enough to require repair. Many shops will not work on a system that has mixed gasses in them.

Either get it fixed and converted, or just fixed and refilled. I personally would convert it, but you can price that out and compare to the rising cost of R12.

I’m not sure what’s happening with the price of R-12, it seems to be pretty stable at the moment. Maybe the demand has gone down in the last few years, but everyone and his brother seems to be selling it on ebay for a decent price (like 30 pounds for a few $100). I’m tempted to grab some for future use, I probably will if the price starts to go up significantly.

I’m going to veer off here a bit.
Should it be done? No.
Can it be done, at least as a short term (year or so) fix? Yes. I’ve done it a few times (long stories) with no problems.

However, you must use 134 with Ester oil. It’s touch and go doing this but it’s possible.

Yeah, I’ve noticed it has seemed to have stabilized. I guess that’s just the old cars that require it are getting junked faster than they are using R12. At some point it will get hard to find, but who knows when that will be. I’m down to 1 vehicle that hasn’t been converted to or started out with R134a, but it’s AC is still working fine so I won’t touch it until it needs a recharge. At which point I’ll convert it.

I have two consumer cans (10-12 oz?) that I have no use for. If anyone wants them and is in the Central Ohio area, post a message or e-mail me. You pick it up, it’s yours.

You CAN NOT, CAN NOT, CAN NOT, CAN NOT, CAN NOT mix refrigerant 12 and 134a together! CAN NOT!!!

Even if you could adapt a hose to deliver R134a to an R12 system, you’d be destroying the system. And NO ONE would work on it for you when it goes.

The same goes for things like Freeze 12. Even though it may blend with R12, NO ONE will work on it for you after that.

If you are simply low on refrigerant, but this has happened gradually over a long period of time (ie, years) then you may simply need a recharge of R12. You may have no leak, and no need to fix anything. Refrigerant leaks out slowly over time, past o rings and through hoses. The design of most A/C systems actually allow for some leakage.

If you have a leak, then your choices are to get it fixed and remain using R12, or get it fixed an convert to R134a. OR you could convert, and not fix the leak, and add refrigerant over time when it needs it. But if the system is ever allowed to empty out completely, air will get into the system and then you will have to have it worked on, or the systemw ill eventually self destruct.

But you CAN NOT mix refrigerant!


I made the mistake of converting one car, I didn’t like the AC performance so I converted it back. I don’t intend to own anything new enough to use R-134a, and I’m not going to convert anything else to R-134a, so I guess I’ll just keep buying R-12. Right now my shop charges about $60/pound, which is OK. If the price starts to go up again I’ll just buy a bunch of it.

Thank you all for your input. That ole Jeep on these 100+ days gets so HOT. It shows 40-45 deg. by meat thermometer up to 11-12am then goes to 60-65. Wiser to just do everything early or wait til evening when pssible. Thanks again guys, enjoy the forum. I will most likely convert, as we did the wifes 90 Toronado. Rex

Of the 3 cars that I’ve had converted I did not notice any difference in AC performance. One had pretty marginal AC both before and after, the others were good with both types. I’ve heard you and a few others say that the R134a doesn’t work as well, but my experience in my cars says it’s not a big enough difference to notice.

I’m not trying to change your mind or anything, just saying my experience was different.

I all has to do with the size of the condenser and the evaporator, if they are large enough the R-134a will still have enough capacity to give you good cooling, If they are sized for R-12 with very little extra capacity, the reduced efficiency of the R-134a will not hack it in really high temperatures.

The AC systems in old german cars are pretty marginal to begin with (sort of an after-thought), if you run them on R-134a they tend to be pretty weak. My car was OK up to about 90F with R-134a, then it just couldn’t keep up. With R-12 it’s good at 100F+, it just wasn’t designed with enough margin for R-134a.

I’m guessing that it’s not something you can package and mail, is it?

Of course a full conversion is the best way to do this, but I have to respectfully disagree with the premise that it cannot work, will not work, and will destroy the system.

About 10 years ago my first SAAB was not cooling as good as it should have and since the temps were about a 105 at the time I decided to give it a go since I had a case of 134 sitting around the house and R12 was 50 bucks a can at the time.

I added a couple of ounces of Ester oil, almost a full can of 134, and the system was ice cold and worked great (35 degree air) for another 3 years until the compressor seal finall gave up the ghost.

Some of those R12 compatible replacements like Freeze 12 and the like are actually R134a and some who-knows-what extra stuff mixed in.

No, 134 won’t destroy your AC system, but mixing it in will likely make it hard to get a shop to work on it. They can’t contaminate their recovery tanks with mixed gasses, and it’s illegal for them to vent it to atmosphere. So, they just won’t touch it. Of course, if you are doing your own work . . .

You’re exactly right of course. There is no way a shop should ever do this and they will refuse to service it.
I’m only speaking from the standpoint of someone dinking around with their own A/C.
At the time R12 was 50 bucks a can around here and the local farm supply store had 134 for 2.99 a can, so what the heck.

Do you still have the r12?

Mr. Meehan ( that maybe just a screen name ) has not been here in years. Also mailing or shipping R12 is not allowed in some states and the others have rules and EPA guidelines to follow.

You joined just to ask if someone from 11 years ago, if they still have 2 cans of R12?