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Why does the Heater/AC Fan never turn compleatly off?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by **DONOTDELETE**, Jun 5, 2002.

    Even though I turn it to the "off" position the heater/ac fan is still on a little bit, and pushes some air out. Why? Anyone else have this problem? Thanks -80K20
     
  1. Mr.Chevy4x4

    Mr.Chevy4x4 1/2 ton status

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    It is what GM refers to as their "fresh air"system. Even in the "off" position the fan will run at a low speed to make sure the occupants have fresh air to breath.
     
  2. 74k5inVA

    74k5inVA 1/2 ton status

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    I would also think that cruising down the interstate at 7o mph that the fan would turn because the wind was hitting it and pushing air up the vents. just like a windmill.
     
  3. TX Mudder

    TX Mudder 1/2 ton status

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    like Mr.Chevy4x4 said, it is supposed to do that, since new.
    I pulled the wire for it because I thought it was annoying. When I get A/C, I guess I'll put it back like it was and live with it.
    -- Mike
     
  4. HarryH3

    HarryH3 1 ton status Author

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    Yep, it's supposed to do that. Keeps fresh air flowing into the cab all the time.
     
  5. YtseJam

    YtseJam 1/2 ton status

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    It also helps prevent spores and mold from building up in the Heater/AC box. So when you get in your truck it doesn't smell like a dirty diaper.
     
  6. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    Most are supposed to do that. I didn't like it, so I replaced my 3 position switch with a 4 position and now have a true off (required slight modifification to the end that plugs into the switch).
     
  7. m j

    m j 1/2 ton status

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    I just killed that by
    pulling the resistor pack out from the heater box in the engine compartment
    cut out the low resistor
    put it back in the heater box
    now the 'off' is 'off'

    there are 3 pins.
    one pin has 2 wires, one from dash and one to the blower motor, that is 'high'
    centre pin is 'medium', current flows through one el cheapo resisant wire
    third pin is 'low/off', current flows through 2 resistant wires
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Not all of them are setup this way. AC setups off is off, as well as the HD heater option. I believe early 80's GM changed the system so that the fan actually shuts off when in the off position.

    IIRC, with non AC vehicles, "OFF" on the fan speed switch means its off. "OFF" on the slider for vent/defrost only=fan running always.
     
  9. Impex

    Impex 1/2 ton status

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    what is IIRC ive seen it mentioned in other post recently but not sure what it means?
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    If I Remeber Correctly. For those of us with extremely short memories : )
     
  11. Mr.Chevy4x4

    Mr.Chevy4x4 1/2 ton status

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    In every Chevy truck I have ever owned from '77 on up(with AC or without) the fan motor has always run any time the ignition switch was on, even when the fan switch was off.
     
  12. arveetek

    arveetek 1/2 ton status

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    Like mentioned before, not all of the trucks do this.

    My '77 Blazer would run all the time, but my '81 and '86 don't. They shut off completely. An '83 C-20 and '86 Suburban I used to have also shut off completely. All of the trucks had/have A/C. I believe that '80 and older trucks have this feature, and the newer ones don't. But I'm not sure.

    Casey
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    My '81-up HD heater says otherwise : )

    Like I said, I haven't seen enough '81-up trucks without AC to know for sure, but I owned an '83 with AC, and the fan shut off. My friend has an '84(?) with no AC and no HD heater, and I can find out what I already know next time I talk to him. It shuts off.
     
  14. BowtieBlazer

    BowtieBlazer 1/2 ton status

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    I have no A/C as a factory option and its when in the OFF position the fan always runs....If I kick it into high speed it blows harder (mind you while still on off) if I turn the high switch all the way past low it turns off completely
     
  15. YtseJam

    YtseJam 1/2 ton status

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    The fan always runs when the ignition is switched on. If it does not run than something is wrong with it. All trucks with or without AC came through this way. And it is said to keep the heater box dry and free of that mildew smell.
     

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