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Re: R-134a vs. R-12 capacities [Re: GMP440] #2516489
07/02/18 05:23 PM
07/02/18 05:23 PM
Joined: Nov 2004
Posts: 507
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340clone Offline OP
mopar
340clone  Offline OP
mopar
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Joined: Nov 2004
Posts: 507
Originally Posted By GMP440
Drive the car around and see how the cooling feels with the R-134 and go from there.
As far as the Freeze 12; yes, I would vacuum the system before filling.
Check and see if the oils in Freeze 12 are compatible with the ester oil you put in when you were doing the conversion to R-134. If not, flushing needs to be done.
At this point before considering the use of Freeze 12, ask others who have used it. There are a/c forum boards that you can get good info from.
It's alot better than trying this and trying that in order to get the desired results with you a/c system.


I agree-good plan. I have yet to actually drive it so it may do alright and not require any further action.

The Freeze-12 use has been long debated. I have heard good things and bad. I have actually added it to R-12 in a 1981 GM system with good results, but I can't say if that was a fluke or not.

The Freeze-12 is compatible with the Ester oil but my concern is whatever oil would be left over from the R134. I'm not sure if it is PAG and if so, how much would you get into the system with two cans of refrigerant? Ester is compatible with both PAG and mineral oils, but not sure about the outcome if the Ester had a little of both mixed in?

Re: R-134a vs. R-12 capacities [Re: 383man] #2516492
07/02/18 05:27 PM
07/02/18 05:27 PM
Joined: Nov 2004
Posts: 507
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340clone Offline OP
mopar
340clone  Offline OP
mopar
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Joined: Nov 2004
Posts: 507
Originally Posted By 383man
Originally Posted By 340clone
After reading about EPR valves, etc. I'm now wondering if I'm going to have problems since mine was not removed? What exactly will happen if EPR remains?

Also wondering now if I should evacuate system again and drop in Freeze-12? Would I have to flush all or part of system? BTW, I filled the system with about 7-8 oz. of Ester oil before I added the R-134. They say that Ester is compatible with either 12 or 134 oils. So what about the oil that was in the 2 cans of 134? Would this cause a problem if I went back to Freeze-12? Or, maybe I should just let it fly as is?

Thanks for any and all help! Sorry for all of the questions. Not really well versed in auto a/c and no one wants to fool with anything this old around here.






The EPR valve is the evaporator pressure regulator valve. Basically it controls the evaporator pressures so it don't freeze up. In AC systems the pressures work right with the temps of it. Lower pressure in the AC system means lower (colder) temps and vice versa. In other words if the evap press gets to low for to long and hangs below about 28 psi the evap can start freezing up on the fins. Keep the evap press about 32 and slightly above and you get cold temps and no freezing evap.
The Fords and GM cars used the same type of valve that they called the Suction Throttle Valve. Most all newer cars have gone away from that system and have gone to cycling compressors to control evap freezing which will turn the comp off if the evap press gets to low and the newest cars may also use variable displacement compressors to control evap freeze up. Some also went away from the exspansion valves to Orfice tubes to control Freon flow to the evap and control the high to low pressure sides. I will admit that all the cars I have switched from R12 to R134 were a bit newer then the cars that used the EPR valve as most or all the ones I have changed were cycling systems that cycled the comp on and off to control evap pressures. So I cant tell you how the R134 acts in that system but some of the others on here seem to have changed that older system and might help you. Good luck with it. Ron


Thanks! I had forgotten about the suction throttle valve in the GM's. I think you are right that most of the cars that were meant to be retrofitted were a little newer than what I am dealing with.

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