Converting R12 to 134a...what pressure?

[ceningolmo]

My green Q is basically out of coolant. Rather that convert every single piece related to the system, I am going to try a shortcut. If it works, great. If not, oh well.

So, I am going to have my local shop evacuate the r12 and then flush the system. I am buying a new receiver/drier for them to install. Then, I am going to have them charge the system with 134a. My question is what pressure they should charge the system? Should I use the pressure guidelines from my 91 FSM (r12), or the pressure guidelines from 94 (134a)?

As always, thanks for the help.

[Q451990]

So you're going to have it professionally evacuated, flushed, and recharged - but with the wrong refrigerant? I would think that you're only one small step away from fixing the system right - which would be to find the leak. Maybe an o-ring or flex hose... if not then you have another issue that will cause it to fail regardless of which refrigerant you use.

I think would understand your approach better if you were going to be doing all of this shadetree... your only expense would be for the dryer and 134a - but to pay someone to come so close to a full repair but use an alternate refrigerant is a little confusing to me

As far as your question about the pressures - I have no idea... how far off are they between the 134a models and the R12 models?

Heath

[green91]

Its not a matter of filling to a certain pressure, its a matter of filling to the correct #s on pounds in the system. Ive done several cars r12 -> r134a. Replacing the dryer is a very smart move.. Ive done msot of the conversion by replacing the dryer bottle and installing r134 fittings. But know that r134 in a r12 system isnt as cool as r12.. but is usually cold enough to passify most people.

When go to charge your a/c system, ask them to use dye also. Its normal for a/c systems to loose a small amount of freon over time, but its sometimes hard to find leaks if they exist and the dye is hard to ignore if you do have a leak.

[ceningolmo]

I would try it shadetree... but, I don't want to buy the vaccuum and assorted other things I would need to do the job right. And, I don't know anyone who already has this stuff...so, off to the local shop I go. The nice thing is that my local guy is really good about letting me pick and choose which things I want him to work on and which things I can do...that lets me keep the labor expenses to a minumum.

As far as pressures... at roughly 77 degrees F and 50-70% humidity...

94 fsm lists pressures as 178-208 psi on the High Pressure side and 27.6-30 psi on the Low Pressure side, while 91 fsm lists pressures ranging from 118-146 psi on High Pressure side and 27-33 psi on Low Pressure side.

[ceningolmo]

Its not a matter of filling to a certain pressure, its a matter of filling to the correct #s on pounds in the system. .

So... since its about the number of pounds... any chance you know the factory fill to use under these circumstances?

[maxnix]

Heath has it correctly. Find the leak, break it down and repair the cause and anything else that is obvious, get a new dryer, evacuate and refill with R12 and the correct lubricant in the correct quantities. Then wait to see how long something you didn't replace will fail.

Trying to get it to work right on R134a is about like getting your engine to run on diesel. Just don't do it unless you want to permanently trash it.

You can't go by pressures unless you are in the ballpark on the fill. Then pressures will tell you on what side problems may lie.

[Q45tech]

Depending on an earlier failure or dealer retro fit you may or may not have very leaky flex hoses! Early R12 hoses cannot be used with R134a because the smaller molecules will just leak thru the hose fast.

You can even buy aftermarket evaporator cores without the expansion valves [need to be swapped over after a clean out and reinsulated etc.

If the hoses are good, the orings at compressor or dryer or the evaporator.

When you fix the system leakage [of R12] should be insignificant allowing recharges every 4 years or so................after all the system when brand new went even longer before the first recharge! Right

Don't let some quick buck artist talk you into a conversion.