R-12 to R-134a conversion

Home  \  Repairs & Maintenance  \  R-12 to R-134a conversion

Greetings all,

I have a 1976 Buick Electra 225 Limited with a 455 cubic inch big block 4bbl. that I am getting prepared to run an R-12 to R-134a conversion on. My question is specific to preparation of the system. I need to flush out the condenser, evaporator and compressor and was wondering what the best way to do this was. I have a buddy that restored a 1971 Ford LTD with a 2bbl 390 CI and he used brake parts cleaner to do the evap and cond. Once flushed, he then blew them out with shop air (which could have moisture in it). As for the compressor, he just gravity drained it as there is no real way that we knew of to "flush" all the mineral oil out and with that, you surely would NOT want to use ANY B/P cleaner on it due to seals and the like. When replacing the R-12 with R134a, I am going to use PAG oil which should be ok if there is a little mineral oil left in the compressor crankcase. It is a BUIG ole York compressor and they are endemically tough as nails still used on big rigs. My buddy's a/c works terrifically and it is ICE cold. I am thinking of trying the same thing as if this works, what is the point in the dollars I would spend using a professional flush kit? The lines are easy to do with B/P cleaner....I was just more concerned with the other components including evap, cond. and compressor. The receiver drier and accumulator assy as well as O-rings will be replaced with new as well as a high pressure switch installed in the high side line. If anyone sees a better way or another way of performing the flush, as long as it is instructive and intelligently and technically stated, please tell me. I think that this should work well though. Thanks!

posted by  cmeseadoin

You just described what in my expeience is the best way to do the job, and I'm talking experience of literally hundreds of conversions. The flush kit doesn't do any better job than the brake cleaner, it's all in taking your time.

The small amount of oil left inside your compressor is unimportant. I personally don't change the high side switch. This allows for higher pressure before kicking off the compressor and if the system is marginal I've seen this increased pressure blow things up, usually the evaporator which of course is the hardest and second most expensive part to change on the system.

Lastly a word of advice, which is an opinion and you know about opinions. Don't replace o-rings just to replace o-rings. If you break a connection then by all means use a new one upon reassembly. What I'm saying is if you don't take it apart, leave the old o-ring in place. An existing good connection won't leak with R-134 and taking it apart may cause a leak. Have fun and freeze your ass off.

posted by  vwhobo

VWHOBO,

Thanks for the reply back....seems I am on the right track. I was just curious in regards to the quote I pasted in below: Currently my R-12 system does not have a pressure switch in the line anywhere that I know of so that is why I was installing one for R134A. I have never done a conversion before, but what I have is a thermal limiting fuse that basically acts like a little circuit breaker that goes between the electrical lines from the power supply to the compressor and the compressor kickout switch for the electromagnetically operated cluth. Now in sitting here trying to determine how that works, what I come up with are two scenarios. Either there must be a sensor that sits in the evaporator enclosure box under the hood that determines how cold the air or evaporator is (like a thermistor) and when it reaches the low threshold of cold, it opens the circuit to kick out the compressor. There is not a pressure switch of any type or kind in any low or high side line on that car. Scenario two is that this is a contant "run" system where the compressor does not kick out unless the "Thermal limiter" sences an overload and acts on a "bi-metallic strip" principle whereas if the current was to overload the circuit, then it would open. Either way, I have been told that when I run R134a in the system, I'll need a high pressure switch right there on the high pressure line at the connection where I screw on a new R-12 to R134a fitting. I'll just wire it right into the electrical wire that feeds the clutch so that the switch bridges that current flow. I ordered all these parts from ACKITS.COM which had all the fitting and I can just screw the High side adapter on and it is like a T connection, whereas the high pressure switch just screws in the other side of it then you run your wiring. I can't wait to be freezing my ass off, LOL. Thanks again for the helpful info! :hi:

[quote]I personally don't change the high side switch. This allows for higher pressure before kicking off the compressor and if the system is marginal I've seen this increased pressure blow things up, usually the evaporator which of course is the hardest and second most expensive part to change on the system.

posted by  cmeseadoin

Your Message