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R12 to R134 conversion

This is a discussion on R12 to R134 conversion within the Classic Muscle forums, part of the Vehicle Specific category; I am going to invest in some tools to work on our cars' AC systems (triggered by the fact that ...

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    '02 WS.6 / '07 Suburban

    R12 to R134 conversion

    I am going to invest in some tools to work on our cars' AC systems (triggered by the fact that the AC in our Suburban died late last year). So far, the list includes a gauge set, vacuum pump, dye, o-ring kit, and a thermometer. Anything else I should be looking at?

    On our play cars, the AC system in our '85 Monte Carlo SS is also non-functioning and I'd like to get it working again. I understand that I have to swap on a set of ports and that they make adapters for this purpose. From the reading I have done on the intrawebs, it appears that swapping out the receiver/dryer assembly is also recommended. I am not certain if the Monte utilizes an orifice tube or an expansion valve and accumulator, although being older I assume it is the latter.

    I also understand that due to the differences between R12 and R134 that I should plan on utilizing approximately 85% of the recommended refrigerant amount and that o-rings throughout the system should be changed. What else do I need to purchase (besides refrigerant) and how does one go about the conversion process? I also have read that installing a larger condensor is recommended as well. I am not sure where to source conversion parts -- any recommendations?

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    Moderator Firebirdjones's Avatar
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    I can tell you how I do it Jeff, I've done several conversions, maybe this will help some.

    On the dryer, I always replace those, as they should be replaced any time the system is cracked open. So for me these are a "given"

    The 134 adapters just screw right onto your existing R12 threaded fittings and turns them into quick disconnects, very simple.

    Your 84 should have an Orifice tube (filter) They cost about a $1 and I always replace them. You may find some trash attached to it if the system has had a failure in the past (that's what they are there for) I haven't seen expansion valves on cars much past mid 70's. My 79 pickup is of the Orifice Tube design if that helps.

    I don't bother with larger condensors, however the reason people mention that is because 134 isn't as efficient and it takes a larger or more efficient condensor in some cases to cool that 134. However if you are dealing with a car or truck that already has a rather large R12 condensor I've found them to work just fine on 134. May not blow as cold sitting still but once moving it's ice cold. Your Monte I believe should have a fairly good size condensor, I wouldn't bother changing that myself unless it's cracked and leaking.

    Since you'll be replace all the old 0-rings you'll have the system apart. What I like to do is take each component (condensor, lines, evap) and spray them out with non chlorinated brake clean and then use compressed air to blow them out. I do this in both directions to make sure I get all the old oil and any contaminents out of the system. This is the most important step so take your time. The condensor and evap can be done while still in the car if you wish.
    If you are still using the same compressor, the best you can do is to tip that on it's backside in a small bucket and let that sit for a day or two to drain all the old oil out. You may not find too much in there but I let it sit a while none the less. I don't care to hose out the inside of the compressor with chemicals as I'm afraid it might be detramental to the seals. Most of your oil will be found in the evap. Once it's all clean, reassemble with your new o-rings. I'll put a small amount of the 134 oil back in the compressor, the rest of the oil (depending on how it's contained) I'll either poor it all in the compressor, or if in the sealed metal can, it will go in through the charging process.
    I like to vacuum it down for about 30-45 minutes with my vacuum pump. After that it should be holding a vacuum if there are no leaks. You can then take your first can of charge (if oil I do that first) and simply plug that in and the vacuum in the system will empty most of that first can without running the system. Then it's as simple as starting the car, jumping the low pressure switch to make the compressor run, and charge the system the required amount.

    Really nothing to it. The cleaning out the system of the old oil is the most time consuming part of the whole deal.

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    Thanks, FBJ!

    Do you simply replace the dryer with a stock replacement part, or does it have to be something that is R134 compatible? Have you ever left the stock O-rings in place with an R134 charge on the older R12 system?

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Thanks, FBJ!

    Do you simply replace the dryer with a stock replacement part, or does it have to be something that is R134 compatible? Have you ever left the stock O-rings in place with an R134 charge on the older R12 system?
    The driers work the same on either system as far as I know. I've never found a specific 134 drier listed anywhere, so I always go with OEM stuff for the model car I'm working on and it's worked out just fine.

    I've never left the stock o-rings in place, simply because I have the system completely apart to flush it out, so I always just reconnect everything with the new R134 green o-rings. That's not to say the original o-rings wouldn't work, because I'd guess they would work okay, I just replace with new because I already have it apart, and it's only about $5-$10 for a complete 134 o-ring kit. That way I also have a better chance of not needing to chase down a leak due to old o-rings that won't compress anymore or possibly have a nick in one.

    On a side note, I've heard stories about original hoses that won't be compatable to 134, I've been told 134 hoses have a different lining inside. But I've never went and replaced all the hoses unless I had one leaking, and these systems have worked fine for years for me with old R12 hoses. I always figured if a hose went bad later down the road I'm only out a few cans of freon, then I'd replace the hose at that point. However years later and the old ones still working just fine for me
    Last edited by Firebirdjones; 06-17-2014 at 10:43 AM.

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    Good to know. First project will be to get the Suburban blowing cold again.

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    Hopefully, the last of the AC tools and supplies will arrive today. I am ready to get started on diagnosing the Suburban leak when they do.

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    Tools should be here tomorrow. I pulled the Suburban in and did a visual inspection of everything under the hood and all looks good. Just for giggles, I hooked up the gauge set and, as expected, the system was completely discharged. I hooked up the vacuum pump in order to get an idea of how sizeable the leak is... and could only draw 5 pounds of vacuum with it snapping back to zero as soon as I shut the pump off. It definitely be a good size leak (or leaks).

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