Auto A/C -- Retrofitting R12 to R134

[Roadman]

    I've been involved in the Auto A/C industry since the 60's so I wanted to share the correct way to retrofit your system, the parts you will need, why you will need them and the procedure to complete the task.

    It's important to keep in mind the fact that the molecules of R134 are smaller than R12. More on that later.

     Parts/supplies need.

     1. Expansion valve.  Most valves today are calibrated for R134. The orifice is smaller which squeezes the R134 tighter ( smaller molecules ) as it passes thru, which will cool as well as R12

      2. Refrigeration oil.  R12 systems use a mineral oil that circulates thru the system. R134, with smaller molecules can't push this heavy oil, so an ester or pag oil, which is lighter needs to be used.

      3. Receiver/Drier. Most all today are compatible with R134

      4. Charging port adapters. These are not necessary if you have R12 gauges and charging hoses. If however your going to rely on a local shop they will need to be used. Also state and or local laws may apply.

      5. HNBR O rings. These are the green O rings used on hose fittings. Always replace used o rings if you take an fitting apart. I always replace all the orings just for piece of mind.

       6. A/C flushing liquid.

       OK, so if your retro fitting a system that's still operational, just leaking R12 make sure the compressor is quiet, good airflow over the condenser, fan clutch working properly, hoses in good condition, and water drain from evaporator not clogged.

       First find the source of the leak. Usually you will see oil residue where it's leaking, ie hose fitting, compressor, etc. Repair leak.

       Now the parts can be removed, INC, LUDING THE COMPRESSOR. It comes off to drain any old oil out of it. This can easily be done by turning the compressor to where the ports are facing down, then turn the drive hub back and forth which will pump the oil out of the discharge port. At this point you can position the compressor so the ports are facing up, slowly add the new oil thru the suction port while turning the drive hub which will suck the oil into the compressor. Consult a fsm for the correct amount to add, usually 6 to 8 ounces. Now the rest of the system needs to be flushed. You can remove the old drier and expansion valve, disconnect hoses @ condenser, then using flush and compressed air blow it all out.

        At this point the system can be reassembled. Due to the fact that the drier has dessicant in it, I always install it last, right before I evacuate the system. It's also important to remember the new oil absorbs moisture, so its best to get everything buttoned quickly.

        Now it's just a mater of evacuating the system , " 1 hour minimum @ 30 inches of vacumm " and charging the system. You will use less R134 than the system used for R12. If your sight glass is clear, the system is overcharged. I use my gauge readings to charge the system. I look for 35 to 45 on the low side, 200 to 300 on the high side. High side pressure is directly affected by air flow over the condenser.

         Hope this helps .   

              I believe @ 1 Wild R/T  posted a list of oils on another forum once. 

       

[71GranCoupe]

Thanks Mark!  Good info like this is always great. 

[RUNCHARGER]

Great info. Thanks!

[jimynick]

Nice post Mark and a good, clear list to follow as well. 

[Cuda Cody]

Nice write up. 

[1 Wild R/T]

Since Mark has done most of the work I guess I should provide info on oil.... R12 systems use mineral oil but as Mark pointed out you can't use mineral oil in an R134 system so your options are Ester or Pag..... Well Pag oil isn't comparable with mineral oil if you use it the mix becomes a nasty sludge.... So for conversions you want to use Ester oil.... 

When you flush the system you'd like to believe you'll get all the old mineral oil out but in reality some oil always hides in the condenser & evaporator headers....

[Roadman]

 Replacing Your RV2 compressor with a Sanden compressor ? Since our factory A/C cars used a EPR valve in the suction side of the compressor to regulate the evaporator temp, rather than a thermostat, this will have to be addressed to eliminate evaporator freeze up.  Bouchillon Performance has a clutch cycling switch, part # 6696. Cost is $22.00. Very easy install, just clamps to the suction line @ the firewall, wires into the compressor wire.