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 at 5:12 PM
  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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