How to service A/C?

Fuselage Years

  1. C Sickness

    C Sickness Member

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    The Air Conditioning is inop on my new 1970 300. It's lost it's charge. Due to the "preciousness" of R-12, I want to service the system "once and done", to whatever reasonable extent that is possible.

    Was thinking of new compressor bearings, shaft seal, oil change, and drier. At that point, pressurize with Nitrogen, leave it for like a week, check for leaks, Vacuum system, leave it for like a week, make sure there are no leaks before charging. Not sure about disturbing and breaking connections that maybe aren't leaking to change o-rings. Thoughts?
     
  2. Sixpactogo

    Sixpactogo Member

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    Probably a better plan than what the AC shops would do. Most would replace the shaft seal & drier, maybe the expansion valve. Vacuum and refill with freon and dye.
     
  3. 413

    413 Well-Known Member

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    Best bet is find a shop that’s works on old Car AC systems. There got to be some down In that area.
    This at home ac work from inexperienced Car owners is seldom once and done. And will cost a lot of wasted time and money. You’d have a better chance of hitting the lottery.

    Anything to the EPR or expansion tube? Are you going to flush anything or replace o-rings at the line connections?

    You’ll come back after a week to an empty system. You leak check immediately when pressure is high. Just like a leaky tire.

    you don’t vacuum it for a week either. Vacuum Down to 30” of mercury and let it sit for 30 minutes. But that’s the last step before charging.
     
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  4. 1970FuryConv

    1970FuryConv Senior Member

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    Is R12 still available, or would you have to convert to R134a? Thanks, Ben
     
  5. C Sickness

    C Sickness Member

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    R-12 is available on resale marketplaces. The consensus here on the forum seems to be that the original equipment compressor is best used with R-12. Fit a "modern" compressor for 134. I did just find 9 cans of R-12 and bought them.
     
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  6. rags

    rags Senior Member

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    you can get cheapie 134a from walmart for $5 a can. ever consider vac'ing it and shooting it with 134a just to see? might be pleasantly surprised. if not you're out $15. i don't have any systems similar to yours, but i do have two GM R12's and one Ford R12 system on 134a. they work great and hold a charge with no mods.
     
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  7. 413

    413 Well-Known Member

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    You are advised to change to a different type of oil in the system and change the orings for 134 refrigerant.

    134 is Not as efficient as R12 so it’s not as cold.
     
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  8. david hill

    david hill Well-Known Member FCBO Gold Member

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    Just to add to the above posts. First the amount of 134a required is less than that of a R12 system. Second test the system fully charged. When test for freon leaks at the compressor, condenser and high pressure hoses should be done immediately after A/C system shut down when high side pressure is at it's highest and leaks easier to find. My 2 cents.
     
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  9. 3175375

    3175375 Senior Member FCBO Gold Member

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    R-134a also has a narrow ‘sweet spot’ regarding the amount of charge compared to R-12. I specifically put about 1/2 of the needed R-12 in my 65 Mustang and it worked great. In a R-134a based system with 1/2 of the recommended charge, I would be surprised if it blew cold air at all.
     
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  10. furious70

    furious70 Well-Known Member

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    If it's been dead a long time I'd go borrow AutoZone's vac pump to see if it holds. If it's not been used for years it might have a very slow leak, it's free to try the vac test first.
     
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  11. rags

    rags Senior Member

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    agree. i watch the pressures and charge 'till the system blows cold. with a system with a low side pressure switch i put enough in so the compressor runs full time at idle and cycles on/off at higher rpm.
     
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  12. 1970FuryConv

    1970FuryConv Senior Member

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    If the AC compressor is old/worn and needs rebuild, who would you recommend to do the job?
    Also, would you pay to have the condenser, evaporator, and heater core repaired? If so, who would do that job well?
    Thanks, Ben
     
  13. rags

    rags Senior Member

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    knowing the quality of the work that you do, if i had a compressor that needed to be overhauled, i'd have you do it.
     
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  14. 1970FuryConv

    1970FuryConv Senior Member

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    Last edited: Oct 18, 2020
  15. rags

    rags Senior Member

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    i did. your trick for propping the brake pedal to keep the master cyl. from draining. used that a few times! thanks!
     
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  16. marty koirtyohann

    marty koirtyohann Member

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    if it has been sitting with no freon in it the epr valve in back of the rv2 compressor has gone bad more inlikly i have a all original so i didnt want to change it over to the new rotery style yhey r putting on cars with out ac . it will use any freo . but if u put 134A in the old rv2 compressors u have to take the valve out. im my personal experance 134a will not work right . some say it dose & some dont . i only use r 12
     
  17. John Kirby

    John Kirby Member

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    Th vehicle may be new to you but the A/C system is 50 years old. Unless you had it rebuilt in the last few years. The hoses can't be trusted and need to be replaced. You need to remove all the R-12 oil too.

    I don't know what chrysler changed between 66 and 70 on A/C units but the basic system should be the same. What I did to rebuild mine was rather involved. I changed the compressor to a sanden unit and converted to R134.
    You may want to but a new condenser, they typically get beat up and have bent fins after 50 years. I highly recommend going to a sanden compressor. They are low cost, and readily available. The old harley v-twin compressor costs over $500 for a new one if you are lucky enough to find one.

    It went like this:
    1. Buy hose crimping tool, new receiver/dryer, hose ends that match existing threaded connections, A/C hose that matches existing sizes.
    2. buy A/C flush in pressurized can from NAPA, disassemble hoses except for outlet hose of evaporator.
    3. remove expansion valve (be careful with the thin temp control pipes connected to it. You will need to keep the large pipe they connect to.
    4. Place outlet hose end in empty milk jug. Use ac flush at evaporator connection and blast A/C flush through it. It will be rather nasty coming out. Flush out all solid lines too. And condenser.
    5. Carefully cut off the crimped connections from the large pipe mentioned earlier.
    7. Using original hoses as a template for new hoses, make new ones. Install them as you go. Install receiver/dryer, and condenser if you bought a new one.
    8. The pipe the goes across the back and drivers side of the engine can be replaced with an aluminum pipe. You will need to use a propane torch and a thin piece of aluminum to braze the threaded ends on to it. My brother is an HVAC guy and has a tool that will bend it to the right shape. Keep the old one as a template and ask an hvac guy to bend the new pipe to the correct shape. It is not easy to clean out the mufflers in the original pipe. The crud in them will damage the new compressor. So I eliminated them. Here is a couple photos of what the finished system looks like.

    IMG_0870.JPG

    IMG_0871.JPG
     
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  18. John Kirby

    John Kirby Member

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    A/C replacement Part 2:

    The cost of doing this is about the same as buying a new compressor. If you scrounge on ebay you can find most of this stuff there. Here is a photo of the tool I have. It has dies for several different hose sizes. IMG_0726.JPG
    You don't have to buy the hose crimper, you can test fit the hoses, mark the correct orientation for the ends with a sharpie and have an A/C shop crimp them for you. Costs a lot less than the $100+ crimping tool. My take on the advantage of doing this is original parts are not available and unlikely they ever will be. R134 is $5 a can, R12 is approaching $100 or more if you can find it.

    Once the system is replaced get a loaner gauge set and vacuum pump from Autozone. Connect the vacuum pump, let it run overnight. Then inject the oil the label on the compressor recommends. Fill with R134 until the needle on the temp gauge reads around 36-38 degrees on the temperature scale.
     
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  19. It's better in a letter

    It's better in a letter New Member

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    I have used R414 as a direct replacement for R12 for many years. No change in oil type or the seal material. Doesn't need barrier hoses either. Much cheaper than R12.
    R134 is a smaller molecular size so it will leak through non barrier hoses.
    I have tried HOTSHOT also but not long enough for a good test.
     
  20. TxDon

    TxDon Active Member

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    I agree with #John Kirby and others, you will be much better off doing an underhood conversion to R134A including new Sanden compressor and modern condenser. I did a LOT of research and did this successfully on my 66 wagon with dual A/C and it still works after two Texas summers. Here is my thread, check it out.

    66 Monaco Wagon A/C Resurrection
     
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