R134 Conversion

[91merc]

How much R134 and ester oil will I need to convert my 85 GM from R12?

[91merc]

Also, does anyone have experience charging an AC system with propane?

[Arquemann]

I believe the ratio for R12 to R134a is 75%, so 25% less R134a than R12. Mine was done that way, but it probably should've been filled a bit more since the comressor cycles pretty often.
Also R134a goes with PAG oil, not ester oil. I used PAG 46 per compressor manufacturer/reman.

[91merc]

I believe the ratio for R12 to R134a is 75%, so 25% less R134a than R12. Mine was done that way, but it probably should've been filled a bit more since the comressor cycles pretty often.
Also R134a goes with PAG oil, not ester oil. I used PAG 46 per compressor manufacturer/reman.

I figured I’d run ester oil incase there’s residual R12, and since it’s a beater car and I’m trying to get my ac fixed for as cheap as possible, I think all I’m going to change is O rings, orifice tube and charge it at home with cans of R134 and gauges

[Arquemann]

Only POE oil dissolves into both R12 and 134a, but if you're disassembling the system, just get a few cans of AC flush or cleaning alcohol. When you're opening the system, you need to seal the drier/accumulator quickly to avoid moisture getting into it (generally replaced when opening a system).
I would be more worried about residual ester oil vs R12, especially if you aren't flushing the system. In that case the POE oil might be a safer bet, not sure though.

I believe my system was filled with approx. 10oz of PAG oil, I'd believe the oil amount would be about the same with ester vs. pag.

[87GrandMarq]

I understand doing it for as cheap as possible but if you don’t do it the right way you’ll end up doing it again and probably have to buy more parts. Use a good ac flush, pull a vacuum, then you’re good to go.

I believe Gadget has used propane in his continental.

[friskyfrankie]

If anyone wants to convert R12 to R134a how is propane involved? R134a is "cheap" enough so why play with other products?

[Kodachrome Wolf]

If anyone wants to convert R12 to R134a how is propane involved? R134a is "cheap" enough so why play with other products?

There’s “drop-in” R-12 alternatives sold in some markets like R12a which is essentially just a blend of propane and isobutane. Probably where the propane idea is coming from.

Heck, propane is a refrigerant as it goes, known as R-290.

[friskyfrankie]

There’s “drop-in” R-12 alternatives sold in some markets like R12a which is essentially just a blend of propane and isobutane. Probably where the propane idea is coming from.

Heck, propane is a refrigerant as it goes, known as R-290.

Have seen propane mixes but my impression is that some folks want to go with straight propane. My point is why not simply go with R134a if you are doing the conversion. If you are not interested in a conversion, sure then there are R12 substitutes - most "illegal" and some merely questionable.

[sly]

propane refrigerant is R290. Grill propane isn't pure enough.
n-butane is R600
isobutane is R600a

Seems like R290 and R600a are the ones that are generally available.

All three should work as direct R12 replacements. As for how much to use... not real sure.

R134a conversion requires using AC flush to clean out all mineral oils from the system and then adding 2oz of ester oil to the condenser, evap, accumulator/dryer, and the compressor (8oz total). You will need to drain the compressor as well and when you add the ester oil, rotate the compressor manually about 10-12 rotations before cranking things up. You may also add an extra oz or two to the compressor as it will blow extra into the condenser after you manually crank it to lube everything. This process helps prevent blowing out seals in the compressor. Replacing the condenser with a newer cross flow will help with 134a cooling, but if the compressor craps its guts into the condenser, then you'll have to replace it. The old style condenser for R12 is a single path through and is easy to flush out. Damn near impossible to flush out the cross flow condensers.

[Kodachrome Wolf]

Have seen propane mixes but my impression is that some folks want to go with straight propane. My point is why not simply go with R134a if you are doing the conversion. If you are not interested in a conversion, sure then there are R12 substitutes - most "illegal" and some merely questionable.

I've seen arguments for R12 cooling better than R134a. R134a does work on a higher pressure than R12 IIRC.

My stuff is R134a and was converted well before I got the car. Stays plenty cold though, and I haven't had a true R12 car to compare it to.

[gadget73]

straight propane does work. I ran in the Mark VII, but the pressures are weird. In order to keep the evaporator from freezing up, you end up with a high enough high side pressure that its not really happy with life, though it does get damn cold.

Just for reference, 32F with R12 is 30 PSI, with R134a its 28 psi, with R290 (propane) its about 53 psi. To get that much on the low side with the stock orifice tube the high side ends up in the 300+ range, which is not where it wants to be. You could probably fix this with a larger orifice tube, but in my case its a Fox car which means the orifice is part of the liquid line and there is no easy change unless I want to hack the line apart and install one of those bullshit repair things that tend to leak.

https://forum.aircondition.com/forum/reference-and-resources/111-r-134a-vs-r12-temp-pressure-chart

What does work better is a mix of propane (R290) and butane (R600). The pressures are a lot closer to what R12 is. Approx 50/50 gets you very much in the neighborhood.

https://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html

one nice thing about propane and butane, per the EPA you can just vent to atmosphere. No ozone problems. It also carries the mineral oil just fine. Down side of course is that its flammable so if you have a leak don't be smoking while you look for it.


R152 (computer air duster) also apparently works well though I've never looked too deeply into it.

[Tiggie]

I'm running a propane mix in my 90, Envirosafe Industrial R134a replacement (unsure of the mix). Similar experience to Gadget with the weird pressures. I decided to keep the high side pressures reasonable and deal with the evaporator freezing due to too low low pressure. Max A/C settings and higher fan speeds keep it from turning into an ice chunk and it blows absurdly cold. It still freezes sometimes. Wouldn't like it on a daily. I do like that it runs with the mineral oil. The ester oil turns to acid if your system is leaky.

If you are just patching up a system, throw some o-rings on it, check the orfice tube to be sure it's clean, and give the propane alternatives a shot if you want.

If you want to do it better, flush and run 134a/PAG.

The weight you need of whatever refrigerant is based on the molar mass of the molecule(s). R12, molar mass 120g/mol. 134a is 102g/mol. So take the R12 amount by 85% and you'll get your number. Really just use the pressure gauges though, if you can get some. I use the cheap harbor freight ones and they work fine.

[gadget73]

just change the orifice tube. By the time you get it out to inspect its probably ruined and they cost like 2 bucks.