I am thinking of a conversion but have been told by auto AC people that there are problems with R134 operation due to the system pressure switches shutting the system down. R134 operates at lower or different pressures than R 12. This supposedly is the case for GM cars with auto AC from about 85 to 93.

Has anyone had to address this issue and had a successful conversion with an auto AC R134 conversion on a 90 or vehicle in the year range above? Any extra work to overcome the automatic features of the system?

 

I did my 87 3 years ago. I did my 89 Camaro 6 years ago. Both are still working well.

 

I converted my 87 three summers ago...no problems what so ever. I even did the lazy conversion, by only changing the fittings and the o rings Most people change the compressor and dryer unit when making the change from r-12. My systems was so open that all of the r-12 and the r-12 oil was out.

The main reason why people have some problems when converting, is when the old r-12 oil starts mixing with the new r134 oil. This mixture gums up the compressor and other parts which will cause some problems, such as compressor failure or problems with the pressure switiches. Make sure the system is evacuated under a vacum, this will prevent any problems.

Hope this helps

 

I did mine last year in July with R134. I had one of the aluminum line develope a leek in it so I lost all of the R12. Bought one the kits from Advanced auto, replaced the dryer, pulled a vacumm and filled it up. Works great. blows the coldest air of any of 3 cars.

 

I did my 87 2 years ago, and it is working great! In fact it is working better than with the R12 (of course the old compressor making a racket for the past few years, followed by a complete lockup might not of helped).

I had it done by a "professional" who flushed the system several times to get rid of the debris from the demented compressor. Replaced the orfice valve with a "variable" orfice, replaced the accumulator/dryer, and the compressor with a rebuilt unit. Also replaced the compressor hose assembly due to a "bubble" in one hose.

Plasticman

 

i switched over to the 134 by draining the system, changing the fittings, one can of oil and 3 cans of freon on our old honda, my chevy pickup and my `90 vette.

 

I switched my 90 over to R134 2 summers ago - still blows nice and cold. I pulled all the fittings apart, flushed the hoses,evap, and condensor, new drier, changed o-rings, added oil, pulled a vac, and recharged. In all that, I somehow managed to fix the leak that emptied out the R12 before I bought the car.

 

Here is the answer to your question. Yes, you need to replace your clutch cycling switch. R134 has lower pressures. Your AC
system does not no about pressures, but it relies on knowing when your clutch is cycling. You need this retro switch. Most of
the novice people will tell you that there system works fine with out it, but there system is not working correctly (at 100%). Their is a big difference in working, and working correctly. My car will "work" on 7 cylinders, but 8 is working correctly....

 

You don't need to replace the switch if the old one is adjustable and working. R134 freezes a couple of pounds lower than R12, so you can crank down the cutoff threshold for a little better vent temp when it's 70 to 80 degrees (forgot it above these temps, it'll never see the cutoff pressure). To see if your current switch is adjustable, disconnect it and look for a screw between the terminals. If there, you turn it counterclockwise to reduce the cutoff threshold, clockwise to raise it. Check out what it's doing by hooking up the low side of a manifold gage set and putting the Controls at max. Disconnect the blower motor and the lack of air flow should cause the low side to drop. Note the pressure that it cuts off (should be 25 psi for R12; 22.5 psi for R134). If you've converted to R134, turn the screw a half turn in whatever direction it needs to go to lower or raise the threshold. Crank the a/c back up and pull the blower motor connector again. Keep at it until it cuts off at 22.5 psi.

Not a bad idea to check this whenever you replace parts - as I found out, the replacement OEM switch now come with the 22.5 psi cutoff. Didn't realize it until I was making ice with R12 (which is what the system will do if you set it too low).

 

Probably should have pointed out that the Low Pressure Switch has little to do with vent temps. That's a function of the volume (fixed) and the temp or pressure of the liquid metered into the Evaporator. That's determined by the air temp at the Condensor and of course it can't give up any heat there unless there's air blowing across it. Trouble is, R134 has a smaller molecule than R12, so the tendency is cram a little more in (creating higher pressures/temps) and R12 systems were designed to turn on the air flow (fan) at the condensor at a much higher (than optimum for R134) pressure - around 200 psi - to meter in just the right amount. So, an R134 system needs something to keep that condensor temp/pressure lower and the OEM design accomplishes that by turning the fans on sooner which is about 150 psi. Only with a conversion, you can't achieve that without reprogramming the ECM/PCM ('90 and above) or designing a new switch for the a/c fan circuit ('89 and below). So to work around this, you need to use about 80% of the R12 volume and some switch to a variable orifice (the metering device) with and without a great deal of success. If you don't want to convert, then get your license to buy R12 on line at www.epatest.com (or any of the sites at www.epa.gov) and buy all the R12 you want. Most broken system need a lot more than gas which in the big scheme of things, is usually the cheapest part of making it work again.