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  1. #1
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    R-12 air conditioning debugging on '93 astro.

    I had a thread related to this before but it fell off the edge of the world.

    I have a 93 chevy astro, it has an R12 air conditioning, and it does not have the rear air conditioning option. The compressor turns on and off and on and off pretty rapidly, like i'm told it would if there is pressure but not enough pressure.

    So I bought an R12 AC gauge, hooked it up to the only side it can hook up (the big side, i would assume its the low/suction side), and with the AC off it shows 65 PSI, which is on the low border of the huge red DANGER section on the gauge (which goes up to 200psi, lol!). When you turn the AC on, the compressor starts cycling like i mentioned, and when it is on, it gets 25psi, which is the top of the green section.

    Is this low or good? Am I supposed to check it with the AC on or off? I was thinking it's an electrical problem with the pressure switch.

  2. #2
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    I'd say low on gas. The suction should be 30-35 psi while running.

    Does your '93 van have R-12 or R-134a? Most vehicles switched over in '91.

  3. #3
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    When I charge my systems I usually don't get 40 degrees out of the vents until the low side is around 30-35 lbs with the compressor running and the engine at about 1500 rpm. What temperature are you getting out of your vents. The compressor shouldn't kick out unless you have a low charge or if there is a blockage, but it sounds like you have a low charge issue. I've charged about 10 different vehicles and the compressor ran non stop the whole time I was charging after I got the pressure up.
    Tmaxx NVee Rusty 2.5R E-maxx Elec Rusty, Xtm Tmaxx

  4. #4
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    Whoops, nofear_maxx beat me to it.

    Most gm vehicles that I've looked at didn't change over to 134a until 94.
    Tmaxx NVee Rusty 2.5R E-maxx Elec Rusty, Xtm Tmaxx

  5. #5
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    It's definitely R12. I thought it was R134a and got a can of R134a and the hose, and it didn't fit

    traxxas_addict: Just to confirm, you are talking about R12, right? I know R134a runs at a different pressure.

    If I got instructions with that gauge, I probably would not have even needed to post this

  6. #6
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    That was on a couple r12 systems that I retro-fitted to r134a, but I'm pretty sure the pressure's should be the same or close to it. Either way you should get at least 45 degree air out of your vents and most of the time 40. I've heard r12 cooled better than 134a so it probably should be at least 40 degrees or lower at a full charge. How much freon did you end up putting in or have you put any in yet?
    Tmaxx NVee Rusty 2.5R E-maxx Elec Rusty, Xtm Tmaxx

  7. #7
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    I haven't put any in. EPA even says R12 cools better, or atleast when the system was originally designed for R12. I haven't checked the vents, and i don't know what to check it with either. I'm pretty sure R12 doesn't run on the same pressure as R134a, but I guess i'll find out.

  8. #8
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    The best thing that I've found to check the temp is a meat thermometer(sp). You stick it in the vent and leave it there for a while. The cabin(interior) air should get to 20 degrees below the outside temp. On my dad's '73 Ford it gets to 30 and sometimes even 40 below exterior! its cold enought to hang meat in there!LOL
    Trucks I own: T-maxx 2.5, Soon to be REVO 3.3
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  9. #9
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    The compressor clutch will be trashed if i run it too long the way it is now.
    By the way, I wonder if i should become an MVAC tech. seems like it might be a neat job.

  10. #10
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    Go check this site out:
    www.epatest.com

    Go to section 609, you can read about it. Its kinda on the epa side of things (properly reclaiming refrigerent, using it,etc). But if I remember correctly, they do have some interesting reading. If you decided to take the test (I think around 20 bucks) and passed you could legally purchase the R12 refrigerent.

    I took the test a while back and learned some things. Plus it is nice if they decide to quit selling r134a to the public, I can still purchase it!

    R12 is a colder refrigerent, but new 134a systems are designed to work with the less efficent refrigerent. I converted several r12 systems to 134a and was pleased with the results. Beats not having any air conditioning!

  11. #11
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    hmm, cool. I still don't know if it needs refrigerant though. Is the gauge supposed to be in the green, blue, or yellow, when it's running?

  12. #12
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    How long does the compressor actually run? If it kicks in and pulls it down to 25 psi immediately and kicks off as soon as it hits that mark then you definitely need more freon.
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  13. #13
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    I would agree with everybody else that it is low on freon. On your dryer (large aluminum cylinder thing) you should find a low pressure switch with wires going up to it. Its job is to turn off the compressor if it is low on freon. As you explain it is quickly cycling on and off, typical of one that is low on freon. On some cars the low pressure switch will also regulate the temp, and will cycle the compressor on and off, but it will not do it very rapidly. In a vehicle that has a proper charge, the lower the pressure (on the low side) the colder it will be. But if the refrigerent is too low it will shut off the compressor preventing it from burning up.

  14. #14
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    Yes, i see the switch with the wires.
    I think it runs for a few seconds after hitting 25.

  15. #15
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    134 a and r-12 usually run at the same pressures. Try to get low side 30 -35 psi and the high side at about 200-225 at idle. The clutch will engage and run continuously at those pressures.You also have to factor in ambient air temp and humidity.If it is 95 deg out and humid the pressures will be a little higher than if it is 80 deg outside.I have a 1987 chevy astro and i saw the temps out of the ducts as low as 28 deg. if the system is undercharged the compressor will cylce a lot more often with lower gauge readings.

  16. #16
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    Hmm, ok. I read the section 609 manual from epatest.com, and did the practice test, and passed

  17. #17
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    Awesome!

    Probably took a while to read it. Hopefully the info was worth something to you

  18. #18
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    It took a while, and it was worth something to me. Now I see why arceeguy told me r12 connectors were both the same size, and mine werent. (They were the same size until 1987, when the high side was made smaller to keep people like me from blowing everything up)

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