Heater, AC, Fans Don't Work

F Body General Discussion

  1. Dave Wilson

    Dave Wilson Member

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    I have lights, headlights and dash, rear defroster, radio but no heat, defrost, or any AC fans. Checked fuses and all appear to be good. Any ideas , ami I missing some connection point ?
     
  2. 80mirada

    80mirada Well-Known Member

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    will the fan run on high, if so the resistor could be bad. if no fan at all the switch could be bad, as could the motor. I would jump the motor to see if it will spin
     
  3. Dave Wilson

    Dave Wilson Member

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    Resistor is good and switch is new ,will jump the motor tomorrow
     
  4. Davesmopar

    Davesmopar Well-Known Member

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    Also if it doesn't start spinning once you put power to it smack it what's a hammer and see if it starts up , if it does then it's a Telltale sign that the brushes has gone bad in the motor

    You can probably smack it with your hand you don't have to use a hammer or a screwdriver just something to jar the brushes
     
  5. Davesmopar

    Davesmopar Well-Known Member

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    Of course make sure it's got a good ground oh, you can always run a jumper wire from a good non grounding source to the blower motor
     
  6. Aspen500

    Aspen500 Well-Known Member

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    One thing, in case you don't know. When checking power and ground at the motor, do it with the motor plugged in (load applied to circuit). On higher amperage circuits, it's very possible to find 12V and ground with the circuit unplugged but with the load applied, you have zip. One strand of wire or a poor ground will check fine for voltage without a load and ohms of resistance will be fine but, it won't carry enough amperage to run the load (motor, headlamp, fuel pump, cooling fan, etc).
    Got burned by that once on an Crown Vic ABS pump way back in the early '90's at work and never forgot. Worst part was, I knew about checking with the load applied but had a brain fart or something that day.:eek:
     
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  7. Magnum Aspen

    Magnum Aspen Member

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    20200111_161737.jpg 20200111_161751.jpg 20200111_160736.jpg I looked at the wiring diagrams in the FSM. There are a few places to check for broken, frayed or poor connections. There is a fusible link that supplies the HVAC system through the ignition switch. It looks like one fusible link supplies only the HVAC system. There are several fusible links for various systems, there is a group under the hood on the driver side. This goes to what looks like a dedicated set of contacts on the ignition switch then to the HVAC control switch. Then the circuit goes to the fan speed switch and resistor and then to the blower motor. You should consider verifying the integrity of each connection, bulkhead penetration and switch beyond the fan speed switch. I have read that fusible links can melt and open, which is what they are supposed to do to protect the circuit, without visible damage to the outer layer on insulation on the fusible link.
    See the FSM pages attached.
     
  8. Magnum Aspen

    Magnum Aspen Member

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    Here are better copies of the FSM pages as the pictures were un readable when zoomed in.
     

    Attached Files:

  9. Dave Wilson

    Dave Wilson Member

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    Much appreciated.
     
  10. BudW

    BudW Moderator Staff Member

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    If car has factory A/C, on the passenger floorboard you will find the blower motor (behind the glove box). If glovebox was removed, it will look something like this (this is the ’80-89 version, the ’76-79 version will look similar).
    20160823_143748.jpg
    There is no mention of year car in this thread.

    If your car is not a factory A/C car, then the above data will not be correct.

    Under the evaporator case there will be a pair of thick wires, one black and other green. The green wire will lead to the blower resistor. The black wire will lead straight to ground via a small screw.
    The ground connection doesn’t give much trouble – but if a repair was recently performed in the area, it is often left detached (unscrewed).
    The blower resistor is not a part that fails that often.

    The possible trouble areas are:
    Melted fusible link (underhood, close to brake booster).
    Blown fuse
    Ignition switch
    A/C controller switch
    Blower speed switch (attached to A/C control head)
    Blower resistor
    Blower motor
    Poor blower ground
    And lastly, a break in wiring harness between any of the above items.

    77 FSM pg 24-50a.jpg

    77 FSM pg 24-54c.jpg
    77 FSM pg 24-54d.jpg

    77 FSM pg 24-51a.jpg
    BudW