R134 conversion/pressure switches

[wolfsburged]

1984 Jetta with the factory SD-508 style AC.

The stock system has no pressure cutout switches, only an engine temp switch to prevent overheating.

I'm converting to R134a. I would like to install at least a low pressure cutout switch.

Looking at later Cabriolets on ETKA it appears that they were fitted with a pressure switch.

Would the pressure rating of an R12 switch be compatible with R134a? If so, I could snag a factory AC line with the switch from a late model Cabriolet.

Also is it advisable or necessary to include a high pressure switch since R134a is going to run at a higher pressure than the stock R12? If so, where can I find such a switch and what rating should it be?

[the caveman]

From 85 on they had seperate low and high pressure switches. Find a MK2 low pressure hose and either use it as is, or cut and weld in the fittings to yours. Then wire the switches in parallel with the temp switch. This will need a bit of looking at the wiring diagram as one switch is normally open, the other closed[if i remember right].

[VW_Commuter]

Why are you converting to R-134a?  R-12 will run at a lower head pressure in the compressor which means less power required to turn the compressor.

[wolfsburged]

Going to R134a because I can't get any R12. And I don't want to run any of that R12a stuff.

[VW_Commuter]

Here's some links for people selling R-12 around your area:

asheville.craigslist.org/pts/1910417931.html
winstonsalem.craigslist.org/for/1913313529.html
winstonsalem.craigslist.org/pts/1897261569.html
raleigh.craigslist.org/pts/1876973321.html
eastnc.craigslist.org/pts/1910661345.html

I used www.crazedlist.org to find those links.  Crazedlist.org is a great way to search all of the Craigslist sites quickly.

R-12 cools better, lets your compressor run at a lower discharge pressure, and uses less Hp.  Also, R-134a is not compatible with mineral oil which is what is used with R-12 so you will need to have your entire system flushed or you will shorten the life of your compressor.  This link, www.allpar.com/eek/ac.html has some good info on the conversion from R-12 to R-134a.

Typically the reason the system loses refrigerant is due to leakage past the o-rings at the connections.  If your system has no refrigerant in it at all then I would replace every o-ring in the system and then have a vacuum test run on the system to see if you've corrected the leakage.  If it holds 29" of vacuum for an hour then I would say you can safely recharge the system with R-12 and enjoy the nice cold air in your vehicle.  If it doesn't hold vacuum then it might be a bad shaft seal on the compressor.  Take a look on Craigslist, the local classifieds, VW Vortex, and here on the vwdiesel.net board and you might find a used compressor that's still good pretty cheap.

Ask around and find a reputable shop and get a quote on what the repair costs would be if you can't do them yourself.  It's probably cheaper to get your current system repaired and recharged then converting to R-134a.

I just got my EPA Section 609 certification from www.epatest.com.  The test is an open book exam, cost me $20.00, and took about an hour to study for by taking practice exams.  Now I can legally buy R-12 and recharge the A/C in my Jetta myself.

Just my 2 cents on the subject.

[wolfsburged]

Hmmm..

My dad has a set of pressure gauges and a good vacuum pump. We checked the system and found no pressure, and were able to confirm also that the compressor clutch engages if jumped. We put in on vacuum for about 20 minutes with no leaks.

Since then we've replaced the heater box. I rebuilt a spare box with a new heatercore and a new evaporator, and all new foam. I replaced the expansion valve at the same time, and purchased a R134a "conversion kit" with all of the O-Rings and the port adaptors. I've replaced the O-Rings at the evaporator and expansion valve already.

Now I've since pulled the motor for a rebuild, and had the condensor out to a radiator shop where it was flushed, cleaned, painted, and pressure checked. I have a new receiver/dryer, and was planning on replacing the compressor as well to get new R134a compatible seals. Regardless of the path I take, I will replace the rest of the O-Rings with new, as well as the reciever/dryer.

I was starting to go down the path of pulling the AC lines to replace the hose with R134a barrier hose. But R12 would be easier and better...