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heater & defroster not working right

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by apairof66s, Dec 6, 2002.

  1. apairof66s

    apairof66s Newbie

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    Location:
    Prescott, Az.
    My sons '70 K5 Blazer has fact. ac,which worked fine during the summer, but now the heater/defrost won't blow hot.
    A mechanic that worked on a different problem said that he would have to see the wiring & vaccum diagrams to troubleshoot this. Anyone have these ???
    Thanks in advance for any help.
    Lee
     
  2. bouncytruck

    bouncytruck 1/2 ton status

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    First, welcome to the board... Post some pictures of your truck if you have them.

    The blower works but there isn't any hot air? Sound more like the cable that changes it from hot to cold is either stuck or disconnected. I doubt it is an electrical problem.

    Anyway, one of the board members was kind enough to scan the wire diarams and post them to the web. http://www.geocities.com/chevroletc1070/wiringdias.html

    Good Luck.
     
  3. RingMaster4x4

    RingMaster4x4 1/2 ton status Premium Member

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    On the passanger side fender there should be a vavle in one of the heater hoses. That workes off of vaccum,If there is with the AC/ Heater controls set so that the heater is on. Pull off the vaccum hose and see if that is vaccum on the hose. If so the vaccum hose is pluged in backwards to the AC/Heater Controls. If it is like mine was some one had just bypassed the controls and pluged it in to the motor so it had vaccum all the time. So if there vaccum on the hose the vavle is closed, if there is no vaccum on the hose the vavle is open and that is not the problem. Or the vavle could be bad, Maybe.
     
  4. swamp donkey

    swamp donkey 1/2 ton status

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    I don't have A/C, but I just got my heater all hooked up. On my '69 there is a flap that is cable actuated that picks between the air passing the heater core, or not. The cable is held on by one of those push on washer things (I don't know what there called).
    You can access the flap through a liitle hole on the inside of the passenger side firewall. You will see a rectangular piece of plastic with a cable going through it, remove that cover and you will see what I am talking about... if your a/c version is the same as my non a/c.
     
  5. apairof66s

    apairof66s Newbie

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    Thanks for all the replies.
    I will put all of this info to work and we'll see what happens.
    Lee
     
  6. Robin

    Robin 1/2 ton status

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    On my factory A/C, that flap was broken (where the cable activated it), so the heater was on all the time... Just what you need in Texas summers...
     
  7. 1972_K5

    1972_K5 Registered Member

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    This may be a bit to simplistic but have you checked/replaced your thermostat? If its gone bad you usually won't get much hot air out of the heater.
     
  8. apairof66s

    apairof66s Newbie

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    Yes,sometimes it's the simple things that hang you up but the thermostat was replaced when the crate motor was installed. The engine does come up to normal operating temp.and the gauge is working good.
    This Blazer is my sons truck and I will have to do more troubleshooting as soon as I can get him to park it long enough to check it out.
    Thanks, Lee
     

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