Switching from R-12 to R-134

by Phil Leinbach, updated 7-27-05 by George Nenadovich

A lot of people, including myself, were upset when R12 became regulated and went from 79 cents to $20 a pound. When R134 systems first hit the market the rumor was "it doesn't work very well." I called a company in Tampa, Florida that specializes in vintage car ac systems to ask what I need to convert my 1965 Buick Special to R134. Their response was "I'm not recommending it until they get it working right." (That comment was about five years ago, 1994) I own a 1995 vehicle with a R134 system that gives me an ice cream headache every time I ride in it, so I knew it could be done. As it turns out, it's really not that big of a deal.

If you are restoring a car and have the system discharged anyway, now is a good time to convert to R134. If your hoses need to be replaced anyway, replace them with barrier hose which has a Teflon liner. Super Parts in Largo, Florida (727-586-5366) can make up barrier hose sets for any car, if you leave it for a day, for about $100. The only down side is the factory hose ends do not have large enough barbs for aftermarket crimps. The best they can do is to use generic aftermarket ends on your hoses which only matters if your car has been restored to concourse standards, the rest of us don't care. If your old hoses are still in good shape, go ahead and use them. Older hoses become glazed on the inside that helps to seal them well enough for R134. A molecule of R134 is smaller than a molecule of R12 and the theory is R134 can seep through non-barrier hose. If a system leaks at a rate of one pound per year (which I doubt it would) with R134, it will only cost $4 to top-off the system.

I started off with a rebuilt A6 compressor from a local auto parts store that cost $69.95 with a lifetime warranty. If your compressor is in good shape, you will need to change the oil by removing the drain plug at the bottom of the compressor and flushing it several times until the flush comes out clean. Also, pour the flush in the suction side of the compressor while you rotate the compressor shaft by hand until the flush comes out the pressure side. Continue to rotate the shaft until as much of the flush as possible has been removed from the compressor. Tilting the compressor at various angles can also help remove the flush. "Air conditioning clean and flush" can be purchased at any auto parts store for about $15/qt or $40/gal. The other ac components must also be flushed. I do this by sliding a spark plug boot over the end of shortened transmission funnel. The spark plug boot allows the funnel to be adapted to a variety of tube sizes. Allow several ounces of flush to gravity feed into the evaporator, condenser and each line to be flushed. Place the spark plug boot on the end of your air hose and blow air into each component until the flush starts coming out the other side. Allow the flush to dwell for about an hour so the solvent has time to work. Now, blow as much solvent out as possible. The flush can be reused if you have someone (preferably someone you don't like) hold a container at the outlet side. This part of the job is a big mess. Allow the collected flush to settle in a containter for a few days so the sediment can go to the bottom. Pour the clean stuff off the top and it can be reused. I can usually capture and reuse 75% of the flush.

With the system clean, it's time for reassembly. Pour 5 ounces of Texaco Capella Synthetic Refrigerator Lubricant in through the hole in the bottom of the compressor and reinstall the plug. Pour the remaining 3 into the low pressure port of the compressor while rotating the compressor by hand. Attach the compressor to the engine. Replace all "O" rings with the green ones (some are blue but that is ok --- don't use black). Remove the expansion valve (that is the thing that goes into the bottom, or inlet, of the evaporator with a round hat on the top about the size of a half-dollar. Leave the expansion valve capillary tube attached to the inlet of the evaporator. When you look at the expansion valve from the bottom you will see a brass cup about 1/2" x 3/8" deep with a hex hole in the middle. Find an Allen wrench to fit the hex hole or grind down a larger one to fit. Ok here's the secret that makes it all work. I charged and discharged the vehicle 10 times to figure this out.

You must eat this article when you are finished reading it. Place the Allen wrench in the hex hole and turn clockwise until it stops turning. Do not force it when it bottoms out! Now, turn the wrench 2.25 turns counter clockwise and that is all there is to it. (update see below)

While the expansion valve is out be sure to check the screen filter on the inlet side for blockage. Use flush to clean it if needed. Place new "O" rings on the expansion valve and install. Install R12-to-R134 adapters to both high and low side ports. The adapters can be purchased at any auto parts store.

The system should now be all closed-up. You will notice I have not said anything about installing a new dryer filter. Leave the old dryer on the system until you are sure there are no leaks. My vacuum pump can also compress air by attaching the manifold/gauge set to the outlet side. Pressurize the system to 250 psi and use a soap solution to check for leaks. If the system holds under pressure evacuate it to 30 inches of mercury for about an hour to make sure it holds. If your vacuum pump does not pressurize, you will have to rely solely on the vacuum test that may not show certain types of leaks. When you are sure you have no leaks, open the system and install the new dryer.

Evacuate the system to 30 inches of mercury for several hours and charge the system with R134. The manifold gauge set for R134 is different than R12. You will also need a R12/R134 "T" adapter for the vacuum pump. Measure the temperature at the vents as the charging progresses. The vent temperature should get into the low 50's when the high side pressure reaches 200psi. I always start out with a low charge and increase it later if needed. An overcharged R134 system will also not cool well because it goes into thermal runaway, which means, the compressed gas will get so hot the condenser will not be able to cool it down. Vintage Air (registered trademark) systems work very well with 175 psi on the high side.

VIR systems (1973-7) work almost the same as an expansion valve system. The spring adjustment is inside the VIR unit and the adjustment is the same. Fixed orifice systems (1978-87) are adapted to R134 by replacing the fixed orifice tube with a variable orifice tube. This, in effect, converts a fixed orifice system to an expansion valve system. A variable orifice tube can be purchased at Super Parts for $18 or Autozone for $35 (you do the math).

Another change that can be done to improve the performance of your AC system is to make the airflow over the condenser more absolute. This can be done by filling the gaps between shroud and radiator, the radiator and core support and the condenser to core support. I used 1/2" pipe insulation (Home Depot) to fill these gaps. The top of the condenser on my vehicle stops about 3" short of the top of the hole in the core support so I used a piece of sheet metal to fill this gap. My system stays cool, even at red lights, without a 20 amp fan.

R134 does have one other advantage over R12. R12 is chlorine based which makes it sensitive to moisture. When moisture gets into an R12 system, it becomes acidic which attacks the metals in the system. R134 does not have this problem. Given a choice, even if the prices were the same, I would choose R134.

With todays modern ac technicians, I have found that only the POA valve needs to be adjusted. Contact www.thepartguy.com to have your POA calibrated on a flow bench. I have used his R134 POA valves on 3 cars and they work great with no modification needed to the expansion valve. The Part Guy can also answer your technical questions should you have any after reading this article.

Shopping List

      Qty            Description 	              Price


	   2ea			port adapters 1 high, 1 low       $3ea

      2ea       #14 fat o-rings for compressor   $2.50/10

      2ea       #12 o-rings                      $2.50/10

      3ea       #8 o-rings                       $2.50/10

      5ea       #6 o-rings (2 w/new dryer)       $2.50/10

      2ea       #2 o-rings                       $2.50/10

      1 qt      AC clean and flush               $14

      1 can     8 oz Texaco Capella Synthetic

                   Refrigerant Lubricant         $6

      4ea	      12 oz cans of R134                $4

      1ea       R134 gauge set                  $100-200

      16ft      1/2' pipe insulation             $8

      1ea       3" x 30" thin sheet metal        $4