R134A Conversion for Factory Air Conditioning

[TexRiv_63]

My new 66 Dodge Monaco Wagon has factory A/C with a rather rare rear roof mounted unit in addition to the usual dash outlets. All parts are there, there are no obvious leaks, and the compressor and controls seem to operate correctly but it does not cool and needs a charge. The PO says it was converted to R134A refrigerant but not done the right way. I would really like to retain most of the original parts but do what is needed to get it working. Who has done this conversion and what were the results, also can anyone share any good resources to get information and buy replacement parts? Thanks for any help you can offer. 

[Matt Harwood]

We fix A LOT of air conditioners here at our shop. Everyone seems to own a car with broken A/C and they say they don't care and never use it, but whey they're buying a car, they INSIST that it be working correctly. Weird. 

 

Anyway, my mechanic, who is a retired GM service tech, says that in 1994 there was initially a big scare about the conversion in older vehicles (like the leaded gas scare) and you had to change seals and rebuild compressors and upgrade hoses and things like that, but ultimately, everyone learned that it's really not that big a deal. In most cases, you can just change the port fittings and O-rings and if it seals up, it'll work just fine with R134a. I'm not convinced that your car was converted to R134a, because that fitting on top of the compressor looks like an R12 fitting, not a newer one (which usually have blue and red caps, although we usually paint them black to help them blend in). You should not need to change any other components and that giant Chrysler compressor will be more effective than anything else you buy today--if it's in working condition. If not, then that's the time to consider a modern compressor or have that one rebuilt.

 

If the compressor is engaging properly and the system will hold a vacuum, then you should be OK by changing the fittings and O-rings, and then charging it with R134a. You should try to find a shop that's familiar with the conversion process and maybe even older cars--there's nothing tricky but you want them to be careful and take functionality into consideration. Since the R134a refrigerant is less efficient than the R12, you will lose some cooling capacity but a good tech can compensate by tweaking the amount of refrigerant in the system. If it takes 2.2 pounds of R12, it might take 2.5  or 1.8 pounds of R134a to make it work its best, but there's no conversion chart that says for sure. That's an experience thing that you can't read in a book--your tech just needs to get a feel for it and test to see what works best. More isn't necessarily better than less--there is a figure that will work best.

 

Surely someone will chime in with more details and probably at least one person will say scary things about changing internal seals and incompatible oils and stuff like that, but in most cases, just changing the refrigerant on an otherwise functional system will make it work. However, I promise it WILL leak and you'll have to give it a shot of refrigerant from a can every spring--sorry,  no way around that, so resign yourself to that slight bit of maintenance. It's possible that if your hoses are original, they will leak pretty badly--the R134a molecule is smaller than the R12 molecule and therefore it can escape through rubber hoses that would hold R12. Modern hoses have a plastic or nylon liner that isn't permeable. Cross that bridge if you come to it, but custom hoses are not difficult to have made and are relatively inexpensive. They should be able to re-use most of the hard lines to which the rubber hoses are crimped so it will look right.

 

Not a big job and don't start replacing parts until you find one that is either non-functional or unable to perform with the R134a. If they're all in good order, then you should be good to go.

 

Hope this helps!

[Marty Roth]

I sent you a PM

[charlier]

About 20 years ago when I purchased my 1985 VW Golf the A/C system was not working because the refrigerant had leaked out. It was an R-12 System right from the factory. I was fortunate in that I had an acquaintance at the time who was/is an engineer for Volkswagen who had been involved with VW models of that time (and before) so I sought out his advice about converting from R-12 to R-134a. He sent me a VW Technical bulletin regarding the conversion which had instructions in great detail. One of the most important  tasks for this conversion was ALWAYS replace the receiver drier if refrigerant circuit is left open. The engineer told me that not following this guideline would virtually guarantee that the conversion would not go well. When my VW's system was converted the receiver dryer was replaced along with all O rings in the system as well as the new fittings. 

 

 

During part of the conversion conversation I asked him about retrofitting the A/C in the VW Rabbit model (the model before the Golf) as well. I will never forget that he advised against doing the conversion in the Rabbit if the compressor in the Rabbit was made by York. He told me that the York compressor VW used in the Rabbit  showed a VERY HIGH failure rate after an R-134a conversion. 

 

My whole point of this post is that one needs to do as much research as possible regarding the A/C system in one's vehicle before doing a conversion.

A/C systems used by various vehicle manufacturers have subtle differences. In most cases those differences are not a big deal. In others they are. 

Assuming all A/C systems are the same across manufacturers and years when it comes to an R-12 to R-134a conversion  might not be the best idea.

 

 

[padgett]

Well I always change the dryer and orifice tube (I like variable orifice tubes) and completely flush the system. Then I pull a high vacuum and leave overnight. If no change then I add "combination" oil (usable with both R12 and R134) and then charge R134 to 2/3 the amount of R12 (it takes less) and finally adjust to an outlet temp at max fan & 2000 rpm of under 40F (usu can make 35F) with an external blower on an 85+ day. Am a bit finicky. All of my cars have factory AC.

 

ps Personally never cared for York compressors, I prefer axial/swash plate units (most GM). Suspect you may need a larger compressor for the dual system to work properly..

Edited May 22, 2018 by padgett (see edit history)

[mcdarrunt]

We evacuate the R12 system, flush with isopropyl alcohol, purge with dry air, replace black O-rings with green ones, replace filter/dryer, fill with PAG oil, charge with 134A. If old system has sight glass you DO NOT charge with 134A till bubbles disappear---it will be way over charged. Best to go by high side pressure reading which is ambient temperature related. The 134A is not as efficient but if starting with a scratch built system then a larger in surface area condenser will help. On cars with exposed radiators (no grill) we use a remote condenser with an electric fan which requires an R12 system to work good at all.

[Frank DuVal]

All good advice. I will add one more item. As soon as the receiver dryer is open to the atmosphere, and this includes the new one, the silica gel inside starts to absorb moisture. That is what it is supposed to do. If one wants to make sure the silica gel has released all of its moisture and turned blue ( not that you can see color inside that metal can?), pull a good vacuum on the system, then pace a heat lamp, or even an incandescent drop light (remember those?) near the receiver dryer to get it warmer than 212 °F. Not much warmer, do not melt anything!?

 

Leaving the system under vacuum for overnight (not with the vacuum pump on or heat on anything) also helps the moisture evaporate out of the silica gel. Then next day, turn the pump on and suck the evaporated moisture out of the system.

 

If one has a tank of nitrogen, that is also a good way to remove the air from the system after running flush through it, or just having replaced parts and the system was open. Also nitrogen is a good way to pressurize the system to leak check. If using shop air to leak test system, use the driest air possible, like air already run through a silica gel tank or refrigerated air dryer. If you flush the system, make sure to add oil.