Converting the R-12 system to R 134a

Converting to R-134a by Jacob Suter

I did the work myself, took a few hours, anyone with any mechanical sense can do this job - here's what it cost:


Autozone refurb pump




Orfice Tube (change this too, if its dirty flush the system)


two spring clamp style ac hose rebuild kits, from autozone...


three cans of R134


5-6 bottles of isopropyl alcohol


10oz can of R134 friendly lubricant


I tore the system down, replaced the pump, flushed the entire system clean with alcohol and let it sit a few hours, then rinsed it with alcohol again and then blew it clean with DRY AIR (if you don't have a good air dryer for your compressor (or have no compressor), get a can or two of good compressed air).. I replaced all my seals, on the spring clamp and screw-together locations with the green color seals, put the right amounts of lube in everything as the instructions on the pump told me, and put it back together...

Refilled it as much as the refill card prescribed for my system, which came up to 2.5 cans... I filled it to two cans, ran it for a SHORT TIME, then the next morning let off about half a can's worth of fumes into a canister I had, then filled with the 3rd can... its worked perfectly since I did this about 2 months ago.. it blows 39-45 degrees on the highway @ 70mph, on "normal" (outside air) with the fan on max, it blows 45-50 at idle on outside air. On both of those the outside air temp was 90-95 degrees. I can't complain about the performance of the AC or the performance degradation to the rest of the car when its running (I barely feel the engine load).

The Importance of Evacuating the System by drbob

It's necessary, and the better you do the job the better your AC will perform. The step of bleeding off some fumes may be part of a solution, but it's not a reliable method.

Air in the system will take up compressor capacity, making the air hot and small but never condensing it to liquid. In the condenser, air and other non-condensable sit at the top of the exchanger, while the condensed freon is drawn off at the bottom. The air actually pigs up condenser capability by limiting the amount of surface available to the freon.

If any gas gets carried over to the evaporator, it just expands without absorbing much heat-- again pigging up orifice tube capacity as well as evaporator space.

If you have a set of good gauges, you'll see the partial pressure of the air in the system when it's shut down. When the system is running, the extra heat load from the lost condenser space really drives up total system pressures, often causing overpressure shutdown if you are lucky, or condenser failure if you're not having the greatest day already. This is particularly apparent at low speeds when low condenser airflow further limits the ability to get rid of heat.

I like to leave the vacuum pump on the system overnight, rather than the 45 mins that most shops consider adequate. Any moisture condensed in the system will be boiled out, and overall performance will be enhanced.

I converted the P-car a month ago to R-134a, mostly because it leaked a few pounds of gas a year. Resealed, with new o-rings, drier, expansion valves (dual aircon) and a fresh charge of polylester oil to replace the mineral oil, it will pull down to about 20f with 75f ambient, enough to freeze your hands going down the road. I adjusted the freeze switch to cut out at 30f, and it's still darn cold. I was just chilling my martini, officer! Meanwhile, a few p-car associates have done the conversion without the evacuation steps, and see temps no better than 45f best conditions, and high system pressures to go along. Sound familiar, anybody?


Converting to R-406a by Jay Kinnard

I have converted a '91 Explorer air conditioner to alternate refrigerant R-406A and thought I would let others know how it went. The cooling seems to be as good or better than the original R-12. This is an initial report since I have less than a week on the converted system.

I chose the R-406A over R-134A because we usually need the full capacity of an air conditioner here in Texas and I had concerns that a home mechanic could not get an old R-12 system clean enough to get long term reliability with R-134A.

Assuming that you had a working R-12 system that just needed new refrigerant, these are the costs that are involved in doing a legal and lasting conversion:


New neoprene O-rings (blue color)


AutoZone 26135

New barrier hose (13/32" and 5/8")


From Pep Boys Auto

Clamps for hose (6)



3S1 and 3L2 unique adapters for R-406


Monroe Air Tech

1.4 pounds of R-406A


United Refrigeration




Total conversion parts cost


Plus taxes/shipping


Unfortunately this Explorer had a locked compressor (ran out of oil) with a burned up clutch so there were a few additional costs:


Rebuilt FX-15 compressor w/new clutch


AutoZone 57132

New accumulator/dryer


AutoZone 33182

New orifice tube


AutoZone 38635

Compressor oil (Type YN-9-A)


Ford F73Z-19577-AA




Total repair parts cost


Plus taxes


My total cost of going from a dead R-12 system with bad hoses, clutch, and compressor to a working R-406A system was about $350 including all taxes, etc. I would guess that I put about 10 hours labor into this repair/conversion but I was taking my time since this was my first experience with the R-406A and the Ford air conditioner. I have done my own work on air conditioners for about 30 years so I already had gauges, a vacuum pump (old refrigerator compressor), and most of the small tools needed for the job.

I have four more R-12 systems that I plan to convert to R-406A when they need service so I was willing to make the following investments to get started:


EPA 609 Technician Certification


To buy refrigerant

25 pounds of R-406A




It will take some time to tell if I made the right choice on the replacement for R-12. If I did, then I will be able to convert five systems for less than the cost of one dealer conversion to R-134A. If I am dissatisfied with the R-406A performance, the manufacturer says they will give me a full refund. Right now the R-406A looks good.

Oh yes, I did get one estimate for repair and conversion to R-134A from a local air conditioning shop known for their high quality work. They wanted $1400 to do the job. I guess my 10 hours of work was equivalent to $105/hr. Better in my pocket than theirs.




Updated June 13, 1999

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