1997 - 2003 F-150

heater fan only two speeds

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Old Apr 11, 2014 | 05:40 PM
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Tschro's Avatar
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From: Eden Prairie, Minnesota
Exclamation heater fan only two speeds

hi everyone, i have 2002 F150 supercrew 4.6L that i am having issues with the heater fan speeds. if I have the fan speed selector on position 1 2 or 3 the fan runs at the same speed (about half speed). If I select the 4th position (high) it runs at high speed. I have replaced the resistor pack twice and replaced the pigtail connector for the resistor pac. Is the fan speed switch my problem? does anyone have a checkout procedure for this circuit? I found a tread in the how to section and I asked the question there but no one responded in 2 weeks +. Thanks
 
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Old Apr 11, 2014 | 11:33 PM
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From: Easton, Pa.
You have some issue with either the switch, harness or the resistor assembly.
To see the circuit, look into a copy of the Haynes manual page 12-34.
High is a straight ground to the motor. The resistor pack is not in the circuit.
Low selects all the resistor in the stack in series.
As you go to 2 and 3 the switch selects taps that have less resistance so the fan runs faster..
This is all there is to the circuit.
Good luck.
 
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Old Apr 12, 2014 | 12:26 PM
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From: Eden Prairie, Minnesota
thanks bluegrass. I do not have a haynes manual yet. Can you tell me specifically which one you are referring to for page 12-34. Or do you know of a documented procedure somewhere on this site I could use? In one of the other threads by Radams 2002 a/c and heater blowing stopped blowing ( in the 1997-2003 library) # 30 response jbrew mentions a M&N test procedure but there isnt a link. I'm fairly new and am just learning how to navigate this site. thanks
 
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Old Apr 12, 2014 | 12:49 PM
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From: Easton, Pa.
Haynes book is #36059 Ford Pickup 97-03.
Testing is as requires for your issue with a VOM meter and logic.
The resistance is located in the cool air inlet ducting because the elements run hot in any fan speed lower than high.
My assumption is that if speeds 1,2 and 3 are the same, there is a wire short and or switch issue.
The circuit is alive but switching is faulty but don't rule out the fan motor until the circuit is proven good..
Good luck.
 
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