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  1. #1

    Default A/C will hold a vac, but won't take freon!

    86 w/a 350. Converted to R134a years ago. Been charged and working since then. Had a small leak recently. Usually I can charge it this time a year and only have to add a can or so through out the summer. Went to pull a vac on it, but wouldn't take the freon. Here's what I've done:

    - Borrowed mastercool pump (1.5 CFM Single stage) and manifold set from AZ
    - Hooked up according to instructions(blue to low, red to high, yellow to pump)
    - Turned on pump
    - Opened low side
    - Opened high side
    - Let it pull to 29hg then let it run for another 30 mins
    - Closed off valves
    - Set for 10 mins to check vacuum (it held)
    - Hooked up freon to yellow hose
    - Opened low side (needle didn't move)
    - ?????

    That's when nothing happpened. No compressor engagement, no can turning cold, no sucking of the freon.

    Don't know if it's the pump or not, but seems like when it was pulling you could here it, but when it got to 29, it just kinda sat there, running, but didn't seem like it was still pulling. Took the hoses off to feel the pressure, and it didn't seem like it was sucking that much. When I pushed on the schrader valve to check it, it just kinda did a "slight breeze" vs. a hiss.

    Am I missing a step?
    Last edited by Crazeetxn; 04-19-2011 at 09:42 AM.
    TNT - Texas

    First - '68 longbed (lady runs stop sign, insurance gives me a check)
    Then - '81 SWB (stupid stupid stupid...sold it thinking I was going to get something else)
    Now - Finally got my '86 (350, Holley 600, 700r4)

  2. #2

    Default

    Does it have any pressure on the high side? I've found in a couple vehicles in the past that they would not pull any freon on the low side until the high side got "jump-started". If the high side has any pressure at all DO NOT OPEN THE HIGH SIDE VALVE. But, if it's still in a vacuum or no pressure, dump a little freon into the high side. It might be just enough to get the compressor engaging and pulling freon in on the low side. Again, NEVER open up the high side valve if there's any pressure over there. The pressure will backfeed into the freon can and turn it into a grenade, complete with schrapnel. If in doubt, don't do it.
    Christopher

    1991 Chevy Suburban 1/2 ton 2WD w/ chevy SBC 350-3/4 ton drivetrain upgrade w/4.10 gears 200K miles
    2005 Saturn ION-2 Stock 265K miles
    1982 Bronco, 1993 Bronco (sold), 1971 M35A2 Deuce and a Half



    There are 10 kinds of people, those who understand binary, and those who dont...

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  3. #3

    Default

    Needle doesn't even attempt to move on the high side. Thought about jumping the cycling switch to see if that'll jump start it. May try to put a little over there and see if that will work.

    Thanks for the input. Wasn't this much trouble in the past..but not doing it that often, was wondering if I missed a step.
    TNT - Texas

    First - '68 longbed (lady runs stop sign, insurance gives me a check)
    Then - '81 SWB (stupid stupid stupid...sold it thinking I was going to get something else)
    Now - Finally got my '86 (350, Holley 600, 700r4)

  4. #4
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    Default

    Is it possible that the schrader valves aren't being depressed by the pins in the manifold hoses? This would still allow the vac pump to pull down vacuum but it would only be in the manifold hoses & not be pulling vac in your AC system. Then when you open the manifold valves it only charges the manifold hoses, but not your trucks AC system. Many times with borrowed/rented tools the previous user has lost pieces & parts. I would double check to see if the pins are even in there, & make sure that they are actually depressing the schrader valves in your AC ports.
    1988 Chevy C-3500 2wd (no pic)
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    L-31 Vortec Heads, Edelbrock Cam & Intake,
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    No rev limiter, No speed limiter lol


  5. #5

    Default

    Thought about that too. Took the quick connect off the low side to relieve the pressure back to zero. Hooked it back up, turned the valve, and presto...a vacuum. I know the needle is supposed to be around 40 when charging, but it won't budge and the sight glass isn't showing a thing.
    TNT - Texas

    First - '68 longbed (lady runs stop sign, insurance gives me a check)
    Then - '81 SWB (stupid stupid stupid...sold it thinking I was going to get something else)
    Now - Finally got my '86 (350, Holley 600, 700r4)

  6. #6
    Sr. Engineer
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    Indianapolis, In
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    Default

    My gauges have a feature that allows one to extend or retract the pins
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  7. #7
    Sr. Engineer
    Join Date
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    Location
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    Default

    If you can,

    Hook up the can to the compressor, and jumper the compressor so it turns on.
    Make sure you have oil in the system. ;)

    This should force it to suck in the freon.....worth a shot.

    But if your system is empty (which it sounds like it is the case), then your compressor may not kick on....thus not suck in the freon.

  8. #8

    Default

    Don't know if this had anything to do with it...when I got the kit, the yellow hose was on the bottom which looks to be controlled by the knob. Did some experimenting and found that if I hooked it up to the top, it seemed to pull better. Sure enough, vapors started coming out of the pump, vacuum pulled, compressor kicked on, and so began the cool down process!!!

    Thanks for all the advice!!!Click image for larger version. 

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    TNT - Texas

    First - '68 longbed (lady runs stop sign, insurance gives me a check)
    Then - '81 SWB (stupid stupid stupid...sold it thinking I was going to get something else)
    Now - Finally got my '86 (350, Holley 600, 700r4)

  9. #9

    Default

    Glad you fixed the issue.
    David
    2004 Silverado 2500 Crew Cab 4x4, AMSOIL EA air filter, Granatelli MAF sensor, Throttle body spacer, Magnaflow exhaust (true dual to 2 in 1 out muffler), 6" ProComp lift (add a leaf and 5" superlift rear block), Bilstein shocks, 35's (Cooper Disoverer ST) and 4.10 gears, Rhino Liner, EGRUSA fender Flares and widow visors, extended stainless steel brake lines, firestone airbags w/onboard air compressor, Pioneer Avic X940BT navigation, Accel backup camera.
    http://www.gmtruckclub.com/forum/sho...Silverado-2500
    1960 Land Rover Series II 88
    2001 Pontiac Sunfire
    2013 Toyota Avalon Limited (Wife's Car)
    NRA Life Member

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