converting from 12R to 134

Heating, Cooling & AC

  1. 69 mayflower

    69 mayflower Well-Known Member

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    I'm in the process of rebuilding my a/c system. All new factory components, but on the fence about switching from r12 to 134. I have read that I will need to take the EPR valve out of the compressor suction side because it isn't compatable with the 134. Also need to change the compressor oil. What if anything is this valve replaced with? Seems like something needs to go back in there to regulate the freon flow. If so, what is it?
     
  2. 65-440

    65-440 Well-Known Member

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    I've done quite a few R134 convertions and never swapped anything....maybe a few leaky seals, be sure to charge system to 85% of the R12 capacity
     
  3. RJRENTON

    RJRENTON FBBO Gold Member FBBO Gold Member

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    USUALLY, the TXV (Thermostatic eXpansion Valve) will likely need to be changed as well, because the different evaporation rate of R-134A is different as the specific heat characteristics of the refrigerant. To control the evaporator pressure, in lieu of the old EPR valve, a pressure cycling switch is installed in the suction line, to cycle the compressor clutch on/off, to maintain an average pressure to prevent evaporator icing (freezing of the collected condensate on the air side of the evaporator). The sensing gas in the TXV operating mechanism needs to be compatible (responsive) to the liquid refrigerant flowing thru the valve, as it (the TXV) is sensing the OUTLET TEMP OF THE EVAPORATOR to prevent flooding, too much refrigerant, or starving, too little refrigerant, resulting in poor performance, or the incorrect superheat temperature.
    Remember also to replace the dryer device, as it will hold several ounces of the old oil. Use a polyol oil compatible with R134A. You are already aware of the needed O-rings needed. Remember also to change the oil in the compressor (old RV-2) or one of the newer Sunden compressors. Hope this helps.....
    BOB RENTON
     
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    • 69 mayflower

      69 mayflower Well-Known Member

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      Thanks for the detailed description. That puts it all into perspective very well and will really help me make my decision.
       
    • Demonic

      Demonic Well-Known Member

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      Use Ester oil, not PAG oil. Ester is compatible with the old mineral oil remnants and 134a. Readily available at most auto parts stores. The FSM has the level check procedure if you're using a RV2 compressor. Oil the aluminum threads in the evap and condenser to avoid galling.
       
    • 69 mayflower

      69 mayflower Well-Known Member

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      Thanks for the tips. I have already made the dipstick as the FSM instructs. This NOS compressor already has the oil in it. Probably be wise to change that out if I convert to 134a. Oiling the threads, I wouldn't have thought of that. Thanks!
       
    • RJRENTON

      RJRENTON FBBO Gold Member FBBO Gold Member

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      You need to drain the oil out of the NOS RV-2 compressor AND MEASURE THE QUANTITY DRAINED. Are you flushing the existing components prior to putting the system?? Upon refilling with the oil compatible with R134A , add the amount drained plus several additional ounces, to allow for the oil in the balance of the system. When the system is in operation, the oil travels with the refrigerant and coats everything in the system....do not exceed the maximum specified oil quantity.
      When everything is reassembled, the system MUST BE EVACUATED to approximately 28 mm of mercury and hold vacuum overnite....which insures leak free operation and most importantly, removes any entrained air, which is a NON-CONDENSABLE, and will inhibit proper operation.
      When handling refrigerants, WEAR SAFETY EYE GLASSES OR SPLASH GOGGLES. Liquid refrigerants boil at very low temperature, ~ - 40° F. and will cause thermal burns......BE CAREFUL.
      BOB RENTON
       
      Last edited: Dec 3, 2021
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      • MoparLeo

        MoparLeo NRA BENEFACTOR LEVEL LIFE MEMBER FBBO Gold Member

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        If this is your first A/C service experience, seek some one with the proper equipment like a good vacuum pump, gauges, scale, etc..orings are a different matrerial as well. It would also be a great time to replace the hoses as they are also different internally from R134 systems.
         
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        • RJRENTON

          RJRENTON FBBO Gold Member FBBO Gold Member

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          I concur....the inner liner of the hoses is different on a R134A system. Because the R-134A refrigerant molecule is smaller than the old R12 molecule, it can diffuse, or pass thru the inner liner, and with time cause a loss of refrigerant. The same thing applies to the various system O-rings. These need to be changed as well.
          BOB RENTON
           
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          • Demonic

            Demonic Well-Known Member

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            All good replies above, including my own, Bob, Leo.

            If you really want to take it to the next level - find a friend in the commercial/industrial HVAC business. They're usually equipped with nitrogen, and a micron gauge on their truck. You can do a standing pressure test with nitrogen (which helps displace moisture when you purge an empty system) and the micron gauge is a finer scale than a std gauge set. If it holds 200 psi nitrogen for 4-5 hrs ( wiggle the flexible parts of the hoses while under pressure gently, like a running engine ) and you can evacuate to 300 microns, and hold that level for 24 hours, you're good.
             
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            • RJRENTON

              RJRENTON FBBO Gold Member FBBO Gold Member

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              I agree....I intentionally did not mention the thermocouple micron gauge because 99.9% of the readers have no clue as to what that is.....I do, and use it when performing evacuation. 300 microns is a good number but much lower runs the risk of boiling off some components of the oil. Sometimes, minor leakage at the compressor shaft seal will occur, due to wear of the carbon vs ceramic seal faces or seal O-rings.
              BOB RENTON
               
            • 69 mayflower

              69 mayflower Well-Known Member

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              All very good information. I have a couple of buddies that are in the industrial refrigeration business that I am going to be asking for guidance and information along the way also. With all of this info and some help from them, I should be able to get this done. All of the components are new unused. I appreciate all of the very helpful information. Thank you
               
            • 72sunroof

              72sunroof Well-Known Member

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              Don't
              12 is still available, yes it is 25 a lb, but it just works better. Would have never converted mine 14 years ago if I had known it is still pretty plentiful.
              I would use nitrogen to pressure test the system after you vacuum it down.
              My 134 does blow at 38-40 in Florida but the calculations and experimentation to get it there sucked.
               
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              • RJRENTON

                RJRENTON FBBO Gold Member FBBO Gold Member

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                The only real problem with R-12 is that its ILLEGAL to own, use or recover it. Just be careful of the FREON POLICE....they're everywhere...... Not sure where you are sourcing from....be it a black market source or someone that recovered it from an old car or ??. The problem with using recovered refrigerant is the potential for high acid (HCl + HF) levels that need to be neutralized to prevent corrosion in the equipment to which it is installed. Also, be aware of the use of FLAMMABLE refrigerants, those derrived from propane, touted to be "perfectly" safe (what ever that is supposed to mean). R-12 has not been manufactured for 20 years. Perhaps one should consider using R-1234yf or similar materials. Just a thought....
                BOB RENTON
                 
              • Cranky

                Cranky Henchman #27 Staff Member FBBO Gold Member

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                IIRC, a product called Freeze 12 is propane based.......had several people mention it to me over the years and have used it too in the 90's.
                 
              • RJRENTON

                RJRENTON FBBO Gold Member FBBO Gold Member

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                I guess its a matter of personal preference......personally, I will not use it because of the safety issues. In addition, ive inquired as to the performance of the "refrigerant" compared to the specific heat characteristics and operating pressures of the origional refrigerant, i was told that information was proprietary. My inquiry was to a person selling the stuff at a national show (Chrysler's at Carlyle)....the person was basically clueless about the product other than it worked "great" (but not in his own vehicle) but was told is was great....without any documentation.....temperatures or pressures.....but it, the product, was just as good as R134A. Oh well...as P.T. Barnum use to say....... just my opinion......
                BOB RENTON
                 
              • Durandal25

                Durandal25 FBBO Gold Member FBBO Gold Member

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                Really? I like this option...can you expand your views on it?
                 
              • Durandal25

                Durandal25 FBBO Gold Member FBBO Gold Member

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                Careful there Cranky......don;t want to see you in a rocket car!
                 
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                • Cranky

                  Cranky Henchman #27 Staff Member FBBO Gold Member

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                  Used it in a 88 Shadow and that thing is loooong gone lol however, it lasted until around maybe 2001 when the head gasket gave up at around 100k miles.
                   
                • 72sunroof

                  72sunroof Well-Known Member

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                  It is not Illegal to own.
                  You need to have a ASE Refrigerant license. It is only illegal to manufacture in the USA. There is plenty of 12 around since demand is very low.
                  1234y is flamible and no real data on how it goes to a 12 system.
                   
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