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What are the relays behind the air filter to blower motor

Discussion in 'Stock 1995 - 2001 Explorers' started by merlow, August 5, 2017.

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  1. merlow

    merlow New Member

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    I think I've determined that the problem with the blower motor is a ground issue. I was following the wire and the tube goes to a relay box where the air filter is. Are any of those relays related to the blower motor? What are they? I can't find a diagram of those.
     
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  3. bobflood

    bobflood Elite Explorer

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    I believe that you will find your blower relay and high speed blower relay in that box.
     
  4. 1998Exp

    1998Exp Well-Known Member

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    If you mean the little box inserted into the air plenum, that's the blower motor speed controller (sometimes called a resistor, but if your Limited has EATC, it's much more than a resistor. Like most of the electronic controls of that era, it's a "low" (ground) side controller. It's inserted into the air plenum to cool the electronics, but even so these are known to fail over time from overheating. If bypassing this box with a direct connection to ground makes the blower run, you probably found your culprit. If you are replacing one, pay attention to the condition of the connector pins on the harness side. They may be burned, and replacement connectors are available.
    BTW: it may be a bit of a fight to R&R this little box. Removing the blower and the CC servo makes it easier.
     
  5. merlow

    merlow New Member

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    I was talking about a box of relays behind the passenger side headlight.
    But you are right I have a controller under the blower motor, not the resistor. I'm not sure what a low ground controller means. If the controller is bad would I still get power to the blower motor but not ground? I get power to the blower motor harness but it won't run until I jumper the ground on the blower motor to the ground screw on the side. Does that sound like the controller? I was under the impression I wouldn't get power if it was bad. Thanks
     
  6. koda2000

    koda2000 Explorer Addict

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    I could be wrong, but I thought the small relay box under the air filter had the relays for the wiper washers and the fog/driving lights?
     
  7. 1998Exp

    1998Exp Well-Known Member

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    According to my 1998 EVTM, this "auxiliary relay box #2" contains the blower motor relay, high speed blower relay, fog lamp relay, and front washer pump relay. The separate high speed blower relay bypasses the resistor when high speed is selected, but this only exists in the manual version of climate control. With EATC, everything is controlled by the blower speed controller. It's worth noting that in both cases, power to the blower is applied through the blower relay, but speed control is on the low (ground) side. If the OP's vehicle is equipped with EATC and he finds power present on both sides of the blower motor, the problem is with the speed controller (or rarely, the EATC itself). Because internally the controller box still has a high speed bypass, it's possible that the blower will work when commanded (or manually set) to maximum speed but not otherwise. That's what happened when mine failed, and it was quite comical: the A/C wouldn't blow any air until it got really hot inside, then the motor would kick in on high speed, cool the cabin down some, stop, and the cycle repeated.
    Incidentally, it's simpler and cheaper to control the amount of current flowing through any device from the "ground" side, and that's why it was designed like that.
     
    Last edited: August 7, 2017
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  8. koda2000

    koda2000 Explorer Addict

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    Yes, I'm very familiar with the difference between the EATC and the manual HVAC blower controls. Not to pick nits, but the blower speed control on the EATC equipped models is called the blower control module. It is used in place of the blower motor resistor (basically copper resistor coils to vary the voltage going to the blower motor) on the manual control model.
     
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