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Discussion Starter · #1 ·
I drove my ShBoom into the garage last nite and parked it. Went out this afternoon to drive it and I could hear this “noise” in the garage. Couldn’t quite Figure out where it was coming from. I got in my car to start it, and the battery was almost dead. Then when I shut the key back off I heard the blower motor continue to run. That was that noise. I can turn key off/on and it doesn’t change. I can turn AC control off/on…keeps running. I can turn blower switch off/on/automatic (this is an automatic ac unit in this car)…keeps running.
I dropped the glove box door down and disconnected the wire going from a “box” to the blower motor to stop the motor.
I’m electronically challenged here so I could use some help. Thanks
 

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97 Thunderbird 4.6, 98 Mark VIII LSC
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It's most likely the HVAC head, but ignition switches acting up do weird stuff like this too. I've observed that if I turn the key partway between RUN and UNLOCK, and stop it in different places, different things happen - the blower motor running full speed with everything else in the car apparently off among them. Another example - turning the key off slightly from run will kill the engine but all the interior accessories stay on.
 

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1994 Black T-Bird 4.6 DOHC TR-3650
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It might be that box you have disconnected (the one with small blades). That is the speed control unit for the fan motor. It might be shorted inside. Disconnect the small wire (coming from the HVAC unit). If the fan does not stops, you have found your problem. If it stops, the HVAC unit or wiring might be the source of the problem.
 
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I could be wrong, but I thought the auto HVAC did not use a blower resistor, the variable speed control is integral to the control unit. Side bar: I'm pretty sure I have 1 or 2 on the shelf if your interested in a used one.
 

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1994 Black T-Bird 4.6 DOHC TR-3650
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If it can help:
 

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97 Thunderbird 4.6, 98 Mark VIII LSC
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Auto HVAC doesn't use a resistor, but it does use a PWM module to amplify the signal from the SATC head and turn it to a high current power source to drive the fan motor. The above shot of the EVTM shows it at the bottom left.
 

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Discussion Starter · #9 ·
I'd start by pulling the auto HVAC unit and unplug the wiring, see if the fan stops spinning. That'll tell you whether or not the control unit is bad.
By “auto HVAC unit” are you referring to the HVAC Controls on the dash?
I ordered and put in a new Speed Control Unit. Put it in and it didn’t change anything.
I appreciate y’all jumping in here trying to help me. Thanks

Thanks! Big help! That cheap knockoff shop manual I have doesn’t have any of this in it!
 
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