converting from R12

[Stephen Richins]

what is the real scoop & what is truly needled to convert from R12. I had a leaking Schrader valve on my compressor so I lost my refrigerant charge so I had it evacuated & recharged with 134. It blows cool enough air for temps in the 80s to low 90s but isn't cold enough for when temps get to the high 90s to low 100s. So my question is what is truly needed to convert from R12 to 134. Also does anyone have any experience with freeze 12 it is advertised as a direct replacement for R12

 

[patrick66]

Replace the dryer and condensor with R134-compatible units. The R-12 parts tend to not work well with R-134, especially in your instance.

 

[73Coupe]

Talk to the folks at vintage air, they are very helpful. When I was looking at doing this previously, I believe it was Curtis from there who explained the process to me:

- Evacuate the old refrigerant, take apart the system and flush it out of all old oil. This would ideally include a compressor rebuild. 134a requires different refrigerant oil than R12.
- Have your hoses rebuilt with new barrier hose. Apparently 134a is a smaller molecule and can pass through the old hoses more easily.
- Remove the EPR valve from the back of the compressor, permanently.
- Install a T-stat up by the expansion valve. Essentially, the old system was engaged continuously and the EPR valve controlled the flow of refrigerant back to the compressor. With 134a, the system is changed to work like a modern system and the compressor is cycled which controls the flow. This is what the T-stat does.
- Install new receiver/dryer
- Not sure if you need a new (recalibrated) expansion valve or not, it might have to be reconditioned anyway.

I probably left out some items but this is it in a nutshell if you're going to do it as recommended by the pros.

I ended up leaving mine with R-12 because I found a guy with some in stock who could charge it for me.

 

[73Coupe]

Replace the dryer and condensor with R134-compatible units. The R-12 parts tend to not work well with R-134, especially in your instance.

Dryer a must, but the condenser is just aluminum tubing and should only need to be flushed out.

 

[Ross Wooldridge]

As above, but the important part about R134A is that you don't put as much in, because the molecules are different sizes and the expansion rate is different . AC works with expansion to gas and contraction liquid. If those rates change to something different then the system's heat absorbtion and cooling capability will suffer.

AFAIK, using R134A in an R12 system has things at about 55-65% of what it called for in R12. So if it's 2 lbs of R12, try it with 1 lb 2 oz of R134A.

 

[Ross Wooldridge]

I agree with most but not all of @73Coupe's notes from the guys at Vintage Air. My comments in bold within his quote:

- Evacuate the old refrigerant, take apart the system and flush it out of all old oil. This would ideally include a compressor rebuild. 134a requires different refrigerant oil than R12. YES
- Have your hoses rebuilt with new barrier hose. Apparently 134a is a smaller molecule and can pass through the old hoses more easily. Not necessarily required - old "seasoned" AC hoses have enough barrier to the R134A molecules. If you use a new R12 only hose, then yes, it will leak.
- Remove the EPR valve from the back of the compressor, permanently. YES
- Install a T-stat up by the expansion valve. Essentially, the old system was engaged continuously and the EPR valve controlled the flow of refrigerant back to the compressor. With 134a, the system is changed to work like a modern system and the compressor is cycled which controls the flow. This is what the T-stat does. YES
- Install new receiver/dryer YES
- Not sure if you need a new (recalibrated) expansion valve or not, it might have to be reconditioned anyway. NOT SURE

FWIW I ran R134A for years and never had to replace an original seasoned barrier hose. Any unions/fittings that I did have to crack apart I did put new R134a compatible O rings in them. Otherwise, if you open them, leave them alone.

 

[BIGBARNEYCARS]

I Agree with removing the EPR valve completely from the back side of that Tecumseh double headed compressor. I converted my 300 Hurst while we were living in Austin, Tejas and removing that valve made all the difference in that Pressure Cooker, Jer

 

[mrfury68]

The charge ratio for R12 to 134 is 20% less than the listed amount for R12. In other words if the amount of R12 required is 3lb.- 4oz, converted to ounces is 52 oz, less 20% is 41.6 oz. which equals 2lb.-6oz. charge. That would equal 3 and a half 12oz. cans of 134. Flushing the oil and changing the expansion valve is a must, as is replacing any O rings or gaskets that you have exposed. I have never replaced any hose unless it was leaking, usually where it meets the fitting. I did my son's '87 LeBaron GTS 2 years ago when I replaced the condenser. 38 degrees at the center vent at idle. Took it to Carlisle and it passed that test with flying colors. It still cools the car down quick today. Hope this info helps. Good luck. BTW my '68 Fury is still running R12, I still have some left I found at a garage sale some years ago.

 

[Davea Lux]

In addition to the items listed above, a major issue with converting to R-134a is that it is a less dense refrigerant. In practical terms, that means it does not circulate the refrigerant oil as readily. The RV2 compressor needs a good supply of oil so that it does not burn out. Usually if the charge drops, even slightly, the compressor gets starved for oil and will seize up because all of the oil has collected in the filter/dryer, evaporator and condenser and stopped circulating. The mineral oil used in the RV2 compressor is not compatible with R-134a and turns into a jelly like snot if exposed to R-134a. This will also fry the compressor.

R12a and the other direct replacements for R-12 are usually a blend of propane and butane and some lesser gasses. This combination works, but is flammable, so keep that in mind when working with R12a. The other issue with R12a is that the lighter gasses in the mixture tend to leak off over time and this results in the system become less efficient.

The best long term solution is to either keep the system charged with R-12 or bit the bullet and go with the Sanden compressor conversion. There are several posts on this site about making that change.

Dave

 

[Ross Wooldridge]

The charge ratio for R12 to 134 is 20% less than the listed amount for R12. In other words if the amount of R12 required is 3lb.- 4oz, converted to ounces is 52 oz, less 20% is 41.6 oz. which equals 2lb.-6oz. charge. That would equal 3 and a half 12oz. cans of 134. Flushing the oil and changing the expansion valve is a must, as is replacing any O rings or gaskets that you have exposed. I have never replaced any hose unless it was leaking, usually where it meets the fitting...

I have heard conflicting reports as to the amount of R134A compared to R12, but in ALL accounts, it's less than the R12 charge weight, not the same, so we agree there. I've heard 20% less to 45% less. What it is likely is that each system is somewhat unique to some degree, and therefore things can vary. So, what I have found best is to add R134A while watching vent temps, and stop when the vent temps bottom out and start to rise. Bleed off a tad, and you're good.

 

[saforwardlook]

In addition to the items listed above, a major issue with converting to R-134a is that it is a less dense refrigerant. In practical terms, that means it does not circulate the refrigerant oil as readily. The RV2 compressor needs a good supply of oil so that it does not burn out. Usually if the charge drops, even slightly, the compressor gets starved for oil and will seize up because all of the oil has collected in the filter/dryer, evaporator and condenser and stopped circulating. The mineral oil used in the RV2 compressor is not compatible with R-134a and turns into a jelly like snot if exposed to R-134a. This will also fry the compressor.

R12a and the other direct replacements for R-12 are usually a blend of propane and butane and some lesser gasses. This combination works, but is flammable, so keep that in mind when working with R12a. The other issue with R12a is that the lighter gasses in the mixture tend to leak off over time and this results in the system become less efficient.

The best long term solution is to either keep the system charged with R-12 or bit the bullet and go with the Sanden compressor conversion. There are several posts on this site about making that change.

Dave

I have to agree with Davea Lux on this one. I have consulted with Original Auto Air in Florida as well (like @73Coupe) and his summary is pretty much what I heard except the guy I talked with said the original a/c hoses after being used with R12 over time have developed a barrier inside that will keep the R134 molecules from escaping, so no need to replace those. So I was considering going that way. But over time now, there have been several folks I know that have converted over to 134A and have had their RV2 compressors rebuilt by original auto air or others and have done what Original recommended and every one of them has ended up with a failed system, usually with a failed RV2 compressor within a year or two. Maybe every one of them did something wrong, but I am leery.

I have elected to go with the R12 as long as I can get it and I replace the condenser with the one from ACGlobal on Ebay as well as the expansion valve and keep using my original RV2 compressor but if the system has ever been opened to air in the past, I will flush out all the old oil and refresh with new original oil for R12 and replace the compressor seal or anything else that is wise to replace and go on my way. There is still a shop in Southern Caifornia that still works on R12 systems and has the refrigerant so I use them - the R12 is expensive but so is a failed R134 system redo.

So far, so good.

 

[Toolmanmike]

I have to agree with Davea Lux on this one. I have consulted with Original Auto Air in Florida as well (like @73Coupe) and his summary is pretty much what I heard except the guy I talked with said the original a/c hoses after being used with R12 over time have developed a barrier inside that will keep the R134 molecules from escaping, so no need to replace those. So I was considering going that way. But over time now, there have been several folks I know that have converted over to 134A and have had their RB2 compressors rebuilt by original auto air or others and have done what Original recommended and every one of them has ended up with a failed system, usually with a failed RV2 compressor within a year or two. Maybe every one of them did something wrong, but I am leery.

I have elected to go with the R12 as long as I can get it and I replace the condenser with the one from ACGlobal on Ebay as well as the expansion valve and keep using my original RV2 compressor but if the system has ever been opened to air in the past, I will flush out all the old oil and refresh with new original oil for R12 and replace the compressor seal or anything else that is wise to replace and go on my way. There is still a shop in Southern Caifornia that still works on R12 systems and has the refrigerant so I use them - the R12 is expensive but so is a failed R134 system redo.

So far, so good.

I don't know if the oil is a big deal. Doesn't the RV2 have it's own reservoir and is self contained. That's the big deal with the new style compressors, the oil that lubricates them travels throughout the system. The R12 system doesn't. Correct me if I am wrong.

 

[saforwardlook]

I don't know if the oil is a big deal. Doesn't the RV2 have it's own reservoir and is self contained. That's the big deal with the new style compressors, the oil that lubricates them travels throughout the system. The R12 system doesn't. Correct me if I am wrong.

The RV2 compressor does have it own reservoir of oil but it too has to circulate throughout the system and it doesn't contain a pump to do that - it is a splash system only at best is my understanding. That R12 mineral oil also absorbs moisture (like brake fluid does) so if the system has been exposed to outside air then it will absorb the moisture and the lubricating properties will decline.

 

[pomonamissel]

man you don't have to go through all that , we used duracool torch lamp fuel , its half the head pressure and less apt'd to seep out , its been 4-5 years in two a/c cars i've done . still 52 degs out the vents . here is the duster . the other was a 69 rivy with a cad engine and gm compressor . no issues

 

[Davea Lux]

I don't know if the oil is a big deal. Doesn't the RV2 have it's own reservoir and is self contained. That's the big deal with the new style compressors, the oil that lubricates them travels throughout the system. The R12 system doesn't. Correct me if I am wrong.

The RV2 compressor has a crank case that is filled when the unit is placed in service. RV2 compressors and all piston type A/C compressors do not have oil rings installed. This allows the oil to flow freely in an atomized state through out the entire system. This is how the top end of the compressor, ie. reed valves and the expansion valve are lubricated. Same idea as modern systems, the oil must circulate. RV2 compressors just use the pistons to move gas and oil instead of vanes.

Dave

 

[saforwardlook]

man you don't have to go through all that , we used duracool torch lamp fuel , its half the head pressure and less apt'd to seep out , its been 4-5 years in two a/c cars i've done . still 52 degs out the vents . here is the duster . the other was a 69 rivy with a cad engine and gm compressor . no issues View attachment 467245

Sure if you use modern compressors filled with whatever you will of course have cold air reliably.

But to many of us, we want the original look underhood and elsewhere - not some modified aftermarket compressor. If I don't see an RV2 compressor under the hood of our vehicles, you might as well leave the hood closed. I could care less......................................and you should be able to do better than 52F?

 

[Davea Lux]

The RV2 compressor does have it own reservoir of oil but it too has to circulate throughout the system and it doesn't contain a pump to do that - it is a splash system only at best is my understanding. That R12 mineral oil also absorbs moisture (like brake fluid does) so if the system has been exposed to outside air then it will absorb the moisture and the lubricating properties will decline.

The RV2 compressors all had an oil pump; some had pressure relief valves, some, the later ones did not. If you take a mirror and look at the back of the RV2 compressor towards the firewall, there is about a 2" square plate with either 2 or 4 bolts. The gear for the oil pump is behind that plate and it runs off the compressor crank shaft. Very similar style gear to the RB engine oil pump. For reference fig# 24-38 in the '70 plymouth service manual there is an exploded view of the compressor.

Dave

 

[pomonamissel]

maybe you are just looking at the duster , that was just one i've converted , it works just as well in stock units as well . i don't have pics of the rivy with its factory compressor those big heavy long gm units . point is no need to change the parts just to fill your a/c units with 134r crap or that costly 12r . a12 is better refrigerant with a lower head pressure about half head pressure that both 12r or 134r . in fact duracool has a whole line of products to recharge or for those first time charges . i'll never use anything else .

 

[saforwardlook]

maybe you are just looking at the duster , that was just one i've converted , it works just as well in stock units as well . i don't have pics of the rivy with its factory compressor those big heavy long gm units . point is no need to change the parts just to fill your a/c units with 134r crap or that costly 12r . a12 is better refrigerant with a lower head pressure about half head pressure that both 12r or 134r . in fact duracool has a whole line of products to recharge or for those first time charges . i'll never use anything else .

Is Duracool flammable? Why doesn't everyone use it? Does it affect the ozone layer? Vehicle manufacturers have to consider such questions legally.

 

[pomonamissel]

yes its flammable , its used as a torch fuel . its mainly butane . but gasoline is flammable to right . and carb's vent to the air , the a/c is a closed loop .