R12 to 134. Whats really needed to do this swap for a great working system. All parts needed?

For those of you in the storm, I hope all is well. We took a good hit and still out of power. Lots of damage. Hope all is well. SUPER SCARY SH&T.

I have looked online and read threads. I want to hear from people who have done this and have a good working system. There is just to much
information out there and some conflicting. For example, did you use the same condenser? For what I understand, your not suppose to use it because its made for a r12. 134 are made differently than r12. See little stuff like that. I know the o rings need to be swapped.

What all is really involved in the swap to make this work correctly? Thanks

My truck is an '85. I am unsure if it came as R12 or R134, from the factory. (It must have been R12, because I had to put the adapter valves) I put on a serpentine belt system from an '88 ish truck and bought a new R4 compressor for a '92 (because that is what I got the hose assembly off of) and a new drier for an '85. I put all new green o-rings, a new orifice tube for an '85, 8 ounces of pag 150 oil and 3 cans of R 134 freon. The remaining components are factory '85. The AC blows nice and cold, even on the 105 plus temp days.

Nasty-LSX said:

For those of you in the storm, I hope all is well. We took a good hit and still out of power. Lots of damage. Hope all is well. SUPER SCARY SH&T.

I have looked online and read threads. I want to hear from people who have done this and have a good working system. There is just to much
information out there and some conflicting. For example, did you use the same condenser? For what I understand, your not suppose to use it because its made for a r12. 134 are made differently than r12. See little stuff like that. I know the o rings need to be swapped.

What all is really involved in the swap to make this work correctly? Thanks

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The only components I changed were the seals in the compressor, all O-rings, orifice tube, and the pressure switch. I still have the original condenser, A6 compressor, and evaporator. I tore the A6 apart and used a ~$25 rebuild kit to swap everything out including a modern double lip seal instead of the carbon/ceramic seal. The biggest part was flushing out all the old mineral oil lube and putting in the Pag 150. The A6 takes ~10oz of oil. You can rent a large AC flush kit from most of the big box stores and run it through each major component before putting the whole thing back together with new green O-rings, new blue orifice tube, and a new filter/dryer with an R134 pressure switch. Mine blows ice cold even after several years of being together. I had ~40 degrees at the vents over the weekend and it was 105 degrees outside with ~50% humidity.

85K304SPD said:

My truck is an '85. I am unsure if it came as R12 or R134, from the factory. (It must have been R12, because I had to put the adapter valves) I put on a serpentine belt system from an '88 ish truck and bought a new R4 compressor for a '92 (because that is what I got the hose assembly off of) and a new drier for an '85. I put all new green o-rings, a new orifice tube for an '85, 8 ounces of pag 150 oil and 3 cans of R 134 freon. The remaining components are factory '85. The AC blows nice and cold, even on the 105 plus temp days.

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My truck also took exactly 3-12oz cans of 134 to be right on the correct pressures.

If the AC is generally adequate, the old style condenser is reasonable. The newer style condenser (flat tubes with zigzags in between, vs the old style with tubes going horizontal through aluminum fin plates) is no question more efficient at rejecting heat. If an existing R12 system cools just fine, converting to 134 should too. But if you have something like a Suburban with a lot more internal volume, or dark paint, no tint, etc. or otherwise borderline system, a parallel condenser will get more capacity than the old style to get you closer to adequate. Down in Houston, I'd probably recommend swapping the condenser, but it will certainly function with the old. More air will help either one, but is especially crucial on 134 systems most of the time.

The rest of it sounds good, Blue orifice tube gets better performance from R134, I think it has white stock? That's common to do, and common to overlook, it isn't mandatory. There's variable tubes that some say work great, others say save your money. I've got no experience firsthand, so do your own research, others may have experience and opinions.

Also adjust your low pressure cycling switch to get better compressor performance. It's usually a slotted screw "hidden" between the prongs on the low pressure switch, adjust until you get the compressor cycling close to ~33° outlet temp on the evaporator outlet line. Others have their method, but short version is that R134 uses different pressures on the low end that will directly affect the evap temps and dash vents. The colder the lines, the better the cooling, but the higher the risk that you start freezing the condensate on the coil, turning it into a block of ice and losing all your cooling capacity. If you've ever had your home AC freeze over and have to turn it off to melt, you've seen what I'm talking about.

85K304SPD said:

My truck is an '85. I am unsure if it came as R12 or R134, from the factory. (It must have been R12, because I had to put the adapter valves) I put on a serpentine belt system from an '88 ish truck and bought a new R4 compressor for a '92 (because that is what I got the hose assembly off of) and a new drier for an '85. I put all new green o-rings, a new orifice tube for an '85, 8 ounces of pag 150 oil and 3 cans of R 134 freon. The remaining components are factory '85. The AC blows nice and cold, even on the 105 plus temp days.

Click to expand...

Most things pre 1995 are going to be R12. R12 was the industry standard during the entirety of square body production.

The rule of thumb is 134A charge capacity is 80% of the R12.

I have done many 134A conversions with zero changes, they all worked well. There are minor differences, since 134A isn’t as good a refrigerant, there is room for improvement. The 134A condensers are more efficient, and I wouldn’t be surprised if there is a difference in orifice tubes.

In a square body truck, I can’t imagine a situation where a factory system converted wouldn’t be acceptable. The interior can space is pretty small compared to a car. I could see the potential for problems with a suburban or crew cab.

If you’re replacing components, make sure they are 134 compatible. Pretty sure anything you buy today would more than likely be acceptable.

The simplest way to go from 12 to 134 without major modifications is to remove all oil and refrigerant from the system, replace the black O rings with green ones, put port adapters on the drier and high pressure line, put PAG oil in place of the linseed oil, and replace the low pressure switch with a new style 134 calibrated one. Also measure the new 134a charge carefully. It should be lower than whatever the factory R12 amount was, due to pressure differences.

Keep in mind, the above method assumes you have an OEM AC system with the R4 compressor. If you try to switch to a modern compressor, you’ll have to purchase or fabricate a mount for it, and modify the fittings on rubber lines that go into the compressor or rig up adaptors for them.

I replaced everything with new. I used a red orifice tube. I think mine took 3 3/4 cans of 134. I probably let some leak out of the cans and hoses. My post comes up in the similar threads below.

Matt69olds said:

The rule of thumb is 134A charge capacity is 80% of the R12.

I have done many 134A conversions with zero changes, they all worked well. There are minor differences, since 134A isn’t as good a refrigerant, there is room for improvement. The 134A condensers are more efficient, and I wouldn’t be surprised if there is a difference in orifice tubes.

In a square body truck, I can’t imagine a situation where a factory system converted wouldn’t be acceptable. The interior can space is pretty small compared to a car. I could see the potential for problems with a suburban or crew cab.

If you’re replacing components, make sure they are 134 compatible. Pretty sure anything you buy today would more than likely be acceptable.

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Agreed. I have done countless 134a conversations with changing NOTHING but the refrigerant. Just pull the system into a vacuum and recharge with 134a. If the system is already in decent operating condition, it will work fine and last a long time too.

Well DAMN, I guess it really is that easy. Thanks everyone.

bucket said:

Agreed. I have done countless 134a conversations with changing NOTHING but the refrigerant. Just pull the system into a vacuum and recharge with 134a. If the system is already in decent operating condition, it will work fine and last a long time too.

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What is the oldest original system you’ve done this too? Did you add PAG oil or just use whatever linseed oil remained in the system? Did you have to adjust/replace the low pressure switch? I’m not criticizing your methods, I’m just genuinely curious.

My sons 92 Yukon had been sitting for 20 years before he bought it. When we decide to tear into the A/C we replaced the head hoses (something had chewed holes in the hoses) I replaced all the o rings, I attempted to replace the orifice tube, unfortunately I couldn’t get it to come out and mangled the condenser, so that got replaced as well. I vacuumed the system, it held vacuum for 3 days while we worked on other things. I figured since it held vacuum, there would be no leaks. HA! After charging and running for a while, the compressor started to bubble around the outer sleeve. Damn compressor would hold vacuum, but not pressure. Replaced the compressor, vacuumed the system (again) charged the system (again) and all was good.

This was originally a R12 system, I didn’t replace the low pressure cutout switch or anything else other that what I previously mentioned. It would blow 38 degrees with ease. Am assuming the condenser was 134 compatible, maybe that was an improvement over the OEM part.

Regardless, it gets pretty hot and humid here in central indiana. While a 2 door yukon isn’t as spacious as a suburban, I think the A/C would be more than adequate on something bigger.

CheemsK1500 said:

What is the oldest original system you’ve done this too? Did you add PAG oil or just use whatever linseed oil remained in the system? Did you have to adjust/replace the low pressure switch? I’m not criticizing your methods, I’m just genuinely curious.

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Darned if I know. I retrofitted a lot of stuff. Many cars of the 60's through '93. I did many things from "blow and go" to full system replacements. But I will say this: if you have a fine working system that will work great on R12, it will work good on r134a as well, with no other changes. Weak components will need replaced, no matter what the refrigerant is.

I'll also say this... yeah, older hoses are not rated for r134a... but that's not to say they don't work with it. They aren't rated for it simply because r134a was not around then. I went to several automotive A/C classes 20 odd years ago when retrofits were a big thing. Most of them were put on by parts supply companies. I'll leave it at that.

i made the AC conversion many years ago to my 1975 K5 Blazer. The only changes I had to make were to convert the High and low pressure ports and install compatible O-Rings. My research revealed and confirmed that the original compressor, condenser and related equipment were all compatible with the conversion. The system has worked perfectly for many years with no leaks!!