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A/C question UPDATE 6-23

Discussion in '1992-Present Chevy & GMC models' started by MTBLAZER89, Mar 25, 2006.

  1. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    In my wifes 99 Tahoe the A/C doesn't blow cold. The rear air works fine, but up front doesn't. How do you recharge the system? Is this a dealer thing, or can I do it myself. How are the two systems separated? Why does one work, but not the other?
     
    Last edited: Jun 23, 2006
  2. sweetk30

    sweetk30 professional hooker Premium Member

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    you have other problems. the freon is all one set with one pump. if the back is blowing cold then there is a door or plug in the front system.
     
  3. 88sub4x4

    88sub4x4 1/2 ton status

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    Yeah, like sweetk30 said, both the front and rear use one compressor, so if it was low on refrigerant both systems would blow warm. Check to see if the blend door is moving all the way to cold, otherwise there is probobly a flow problem through the front system only.
     
  4. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    Damn that is not what I wanted to hear:mad: Oh well I'll check out the blend door.
     
  5. AzzKicker

    AzzKicker 1/2 ton status

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    Actually that is what you WOULD want to hear :) replacing Compressor or other A/C parts in the engine bay is expensive and harder.
     
  6. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    OK I read on fullsizechevy :rolleyes: (I know I know) there are 2 evaporators so that could be a problem. How do you check individual A/C components? Upon closer checks the front air gets cooler, but not as cold as the rear. How can I check the blending doors?
     
  7. HarryH3

    HarryH3 1 ton status Author

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    Have you checked the pressures? I've read somewhere that the front system uses an orifice tube to create the pressure differential while the rear system uses an expansion valve. Perhaps one works better with low system pressure than the other? If so, then adding a bit more refrigerant could fix it. :)
     
  8. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    No I haven't checked the pressures. Where and how do I do that?
     
  9. HarryH3

    HarryH3 1 ton status Author

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    You need the proper gauges. Paid about $50 for mine, on sale at Harbor Freight. You really need to know what you're doing though when you add refrigerant. If you open the wrong valve on a hot day, you can feed 300+ PSI back into the can. NOT a good thing!
     
  10. ryan22re

    ryan22re 1/2 ton status

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    my guess is one of the temperature actuators. or more than one. only way to tell is to find them and make sure they are moving when commaned to full hot or to full cold.

    or the orifice tube is plugged in the front system. if thats the case, the rear will plug soon and probably needs a compressor. and when the rear plugs will need an expansion valve.

    never really seen them leak. except from the compressor.
     
  11. HOSS874X4

    HOSS874X4 1/2 ton status

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    ac control head is bad
     
  12. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    Well I pulled the bottom cover of the a/c heater box under the dash. The evaporator I think thats what it is. Looks like a heater core, but cold LOL any way the lines to it and the evaporator itself are very cold. I can't see up in there to tell how the air blows across it. Does the fan ALWAYS blow through the evaporator? It appears to, but I don't know. If the evaporator is getting cold, but the air isn't coming out cold ????? Whats the deal here? The flapper door between the heater core and ac duct seems to work properly closed when on cold, and open on warm. The vent selector doors also appear to be working correctly. Has anybody actually taken this stuff apart that can help me?

    Help its getting hot:crazy:
     
  13. ryan22re

    ryan22re 1/2 ton status

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    The evap core should only be cold when the a/c is on, and air always blows across it. If its getting cold, it would have to be an actuator. They aren't the most reliable things in the world (the actuators). I really can't remember which ones (should be two if its dual zone a/c). But you should be able to watch them move or not move when you change the setting from cold to hot.
     
  14. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    Yeah the flapper door in between the heater core and evaporator is working correctly. Could the evap fins be plugged or something? The evap only gets cold when AC is on. Seems like a ****ty system to me with the heater core directly underneath the duct that carries A/C. That ****er gets hot:eek1: Maybe just low on 134 and the heater core is overriding the cool air, but the rear air isn't affected so it feels colder?? I dunno. What can be wrong withthe evaporator? Whats this stuff cost to have looked at?
     
  15. ryan22re

    ryan22re 1/2 ton status

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    Depends on the shop, at far as how much. Could be a couple pounds low and the rear just happens to be getting all of the flow. Should hold somewhere around 4 lbs of r134. So I would estimate 1.4 hours to evac and recharge and add ac dye. so at $80 bucks an hour, thats $112 bucks labor 7-10 bucks for the dye, and $20-30 a pound for r134. Maybe $200 if thats all it is.
     
  16. 4xcrazy

    4xcrazy 3/4 ton status

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    Are you sure your heater control valve, under the hood, for water flow, is completely shutting,,,,i had this problem and i usually just bypass it every summer.

    If this is letting hot water through, even when you have the ac on, the heat will override the AC very badly.
     
  17. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    so the heater core is not supposed to get smoking hot when the A/C is on?? That could very well be the problem:mad:
     
  18. ryan22re

    ryan22re 1/2 ton status

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    As far as I know, there is no such valve. Hot coolant always runs through the heater core. And always through the rear heater core as well.
     
  19. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    My truck never had one either , but the newer ones do , even the later R/V trucks from what I have heard from some friends with later model rigs .
     
  20. MTBLAZER89

    MTBLAZER89 3/4 ton status Premium Member GMOTM Winner

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    well that valve sounds better than cracking the A/C system open for parts replacement. Easier too.
     

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