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R134a conversion didn't include new highside fitting

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    R134a conversion didn't include new highside fitting

    Some years ago, I had some AC work on my 91 Ford Ranger. At that time, they converted me over to R134a. Fast forward to the present; I just noticed that the high side has an R12 fitting. Was there a reason they didn't they change that over? I'd like to connect my 134a gauge set but the high fitting doesn't match. Is there a way I can check the high side without evacuating the system. All the adapters I've seen require removal of the highside Schrader valve. If there is an easy way to do this, could you please send me a link to what I would need?

    No way I know of to install a fitting on a charged system. You could use an R12 hose attached to your gauges to read the high side, but unless you have a real reason to, you are more likely to cause a problem than solve one.
    Next time the system is opened, have the correct fitting installed.


      Ford and associated vehicles pre 134a used a smaller threaded high side OE fitting. You would use an adaptor to use had it's own Shrader so both fit R-12 gauges. The retrofit kits USED the OE Shrader on those OR if a right angle adaptor was needed take that out and new adaptor for 134a would have the larger Shrader. Pull hair out issue. Is it a FORD system or a Mazda? You may not know they used both.

      Cars/trucks are made with no high side fittings anymore you don't really need it but is handy or another place to leak.

      Get a cheap infrared thermo and just take the temperature right there, metal part of line convert the temp to what pressure it is when charging. Stop short of a usual 80% more like 65-70% of any known (look for sticker they are NOT all the same) and go up, ounce by ounce from there on a day when A/C is working hard enough.

      This takes hours to tweak out unknowns like this try to make your own perfect # of ounces that works best. WRITE THAT IN PAINT UNDERHOOD! Your call but was legally required to add a HPCO in line (don't) and expect to lose 20% of cooling BTU. It's real close if return line is cold/cool and if enough humidity (most places) will eventually drip condensate.
      STOP THERE. Don't be greedy and add more it will just make you start all over again. Been there, done that, got the T-shirt!
      MetroWest, Boston


        You should be able to buy an adapter to adapt your high-side hose to R-12, but you'd still need the R-12 high-side adapter as high side R-12 fittings were smaller by 1991. I use such for my 1988 R-12 Mazda truck, bought that adapter years ago. Of course once government mandated smaller size for R-12 high side fittings, Ford & Mazda used one size, and GM & Toyota used the other (I have one of those adapters too.

        I had thought there were screw-on R134a fittings available for these conversions though. The owner or shop that converted this 1991 should've installed an appropriate high side fitting for R134a.....


        • Ranger Rust
          Ranger Rust commented
          Editing a comment
          I really appreciate yours and all the other comments I received about this. They were really helpful. I thought that high side looked smaller than I remembered. I've pretty much done all my work on the old 91 ranger, practically rebuilding the rear frame and suspension. I hate that the AC is going to beat me. I'll probably take it somewhere and have them install the proper fitting for R134a. Knowing the high side reading is a great dianostic tool. I wonder if you knew the answer to this. Do shops who retrofit the older AC systems generally not install a proper high side fitting to R134, or did I find someone taking shortcuts?

        Shortcuts, Likely didn't have the fitting i stock, so left it off. Only cars used a "funny" high side fitting, everything else (Heavy truck/ AG) used normal 1/4" flare on R12 highside.


          OP, unless it's destroyed you should be able to just get that fitting. Bring the cap to it's original. It's that size I think 3/16th with Shrader. You leave that Shrader on most the adaptor for 134a is or should be adjustable to push a pin looks like a Shrader that really pushes the OE one. If needed the old Shrader is out and new fitting has the larger one just like for common tires except larger, 1/4" just measured from the dual tipped tool in front of me.

          It is nice to have it there and working no question. I use high sides to put a full vacuum, with purges lines of a gauge set (ancient still works as new) Robinaire (Snap-On) set with just thread on ends for 134a have had to use left over FORD high side Acme fittings for still R-12 cars working since new. I write underhood so no mistakes as there are so few around I'm not replacing the adaptor before any of this madness EVERYTHING used R-12. GM and Ford used different high side sizes s + seems the rest of everything both the same size.

          The "Big Three" US auto makers plain bought up other companies or another made the vehicle just the nameplate changed. Ford has used Nissan's intact, Mazdas intact and Jaguar to name a few. GM has used Suzuki, Toyota and more that I'll forget. KNOW what you have the door jam hopefully matches it's VIN # still says a lot like month/years made and where either in English or in the VIN down to exactly which drivetrain was used OE for this.

          If a real Ford I don't think sight glass was still used on anything well hidden on some this and older.

          Refresh now ancient for vehicles is kits had all possible fittings and up to a full charge of oil for retrofits sold everywhere Ester oil included compatible with any left over mineral or call paraffin oils.

          Said somewhere you were supposed to add a HPCO (high pressure cut out) that would halt the power to compressor if too high to prevent a blowout of the EVER DEADLY (not) R-12, the liquid GOLD of all refrigerants. Also were suppose to change all rubber to green for "O" rings and hose to "barrier" type as inferior 134a was smaller molecules leaked thru the rubber! It wouldn't now this long later I still own plenty OE hoses and used 134a no wild need for an extra tidbit of BTU of cooling where I am and certainly not a pick-up truck's smaller cab at that a small pick up truck.

          Today's game is no high side ports at all. Just always pull down the entire charge with a machine the both cleans and weighs what came out and set to the gram how much to put back after it automatically vacuums out system and it held while you weren't even there it did it by itself.

          THAT ISN'T AFFORDABLE for most shops around me at all A/C is seasonal except for accident repairs mostly. It's put away already if you did have it a waste of space with lots of other things to repair/service ongoing.

          If you still want the thing this site is funky - try to private message me is NOT suggested but tell me a contact address I give you what you need I must have a bag full left over FREE - I'm not here to make $$ rather share a life of this grief sometimes :-)
          MetroWest, Boston


            What about https://www.originalair.com/ford-chr...aight-14-122-2


              Thanks for that link, Cusser. Unfortunately, their ad says it requires removal of the existing schrader valve, which I wanted to avoid. I purchased some like that, but they still need to be adapted to fit the smaller valve Ford installed on it's 91 Rangers.


                Then I'd just use an R-12 hose (or hoe adapter to R-12) with an R-12 high side adapter for Ford. Easier and cheaper.


                  Yep, get the little adaptor for the smaller R12 fitting, it converts to a std 1/4" flare, remove the valve core on the 14" end and install a std 134a adaptor (so you can hook up to your 134a gauges)
                  You will loose a small amount trapped in the adaptor when you disconnect, but the best you can do until you discharge the system and make the change correctly. Doesn't solve the problem you want to solve, but is a work around for the time being.


                    Here's a kit that contains about all fitting for assorted retrofits NOS. It's on Ebay but shop where you wish. I'm still telling you that you don't need it at all in that you can and have to work with low side ports only. If you insist on HPCO that's an additional switch where there was none. It just cut off with pressure too high so it doesn't blow out.

                    I said I'd send the dang fitting to you but didn't hear back. I need contact info (keep it private, use Private Messages) it's COLD already here but can find one. Adjust as needed if there's fake Shrader just pushes on OE one. If too tight they leak! That's why IMO don't do it you don't need it anyway.

                    > Ebay link. Just look and they'll hit you like spam with cheaper ones this kit is about $25 . here > Auto Air Conditioner R-12 to R-134a Conversion Retrofit Kit w/ Oil and Fittings | eBay
                    Last edited by Tom Greenleaf; 09-29-2021, 05:36 AM.
                    MetroWest, Boston


                      Hi Tom, thanks for the offer of the fitting, but I think I'll take your advice and just not bother with the high side. If I ever need a diagnosis I'll just take it somewhere. At least I managed to get the old truck drivable myself, but I'll leave the AC to the experts. I did learn a lot from these posts. Best!


                        Offer stands, just ask. It's somewhat useless I'VE beat on that as you'll never know what a retrofit that had a problem (leaked out) and R-12 is and went nasty costly so cheaper to swap over.
                        That smaller size is close to a tire valve step on ordinary things for FORD for quite some time. It just prevented folks from adding (common once) from a can tap to what could blast wild high pressure, blow up the can and really hurt you.
                        They sold those cans (real R-12) for air horns - athletic games and Coast Guard required for at least ocean boating. I grabbed a ton and gave folks the newer could use in cars/trucks.

                        Don't forget the Shrader tool if you keep going you'll need one. Couple bucks one tool (common to me) has one end like tires the other larger for most retro fittings.

                        Again as it wrecks the job putting them on. Old Shrader is used and looks like a Shrader on new adaptor may have to back off or have a constant leak right away - arggh.

                        So things vary for it if good at old cars they hold a much higher weight can "touch/feel" where it's right on a couple warm to hot days see about where it's good for a season or more? If DIYing this buy up some 12oz cans now or better where I am the dump inventory rather than send it all somewhere NOT very poplar + too cold to know or do much about it.

                        Again - good luck, the world was frantically converting cars the assortment of kits were dirt cheap but tough on proper warnings and instructions got a nick name "DEATH KITS" SOME WITH A SEALER THAT HARDENED WITH ANYLEAK TO MOISTURE LIKE HARD PLASTIC WRECKED CHANCES OF EVER FIXING THAT ONE!

                        Have a good day,
                        MetroWest, Boston