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2005 HVAC blower only works on 'High'

O'Rattlecan

Redneck Prognosticator
26,687
797
Belton, MO
My 2005 F150's HVAC blower quit working on settings 1, 2, & 3. It only works on 4 which is the highest setting. This is getting very annoying and I decided to put in a new switch to fix it. The new switch did not do the trick and it's still running only when I switch it to '4'.

These trucks are too complicated to just dive in and start trouble shooting.

Does anyone have any ideas? Are there any TSB's out there?

Ryan
 

73F100Shortbed

That's how we roll!
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Last edited:

john112deere

caffeine junkie
Staff member
10,807
405
central Vermont
Of course they're still using resistors.

How else would they do it?
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
Check the link I posted. It's not a hamster in the wheel spinning the motor around ;)
 

O'Rattlecan

Redneck Prognosticator
26,687
797
Belton, MO
They have a module for everything. And if a resistor was shot, it probably wouldn't behave the way it was behaving. It would be on high on all settings, or it wouldn't work at all.

Does anyone have any experience with this problem or are we just throwing darts at the board? :D

Ryan
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
No when the resistor fails in only works on the high setting not 'high' in all settings.
 

john112deere

caffeine junkie
Staff member
10,807
405
central Vermont
Seriously, dude- that's textbook bad resistor symptoms.

Replace the damn thing for $20.

EDIT: the reason it's not on full-speed on all settings is because the resistor fails open, not closed. It still works on high because the high setting bypasses the resistor.
 

73F100Shortbed

That's how we roll!
5,937
320
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I will bet on it since I've replaced at least 75 resistors in the past all with the same symptom and fixed the problem every single time. How about if I win we switch statuses for the day? :D I get to play 'admin'
 

DNFXDLI

The Token Canadian
Staff member
Ryan, my 2005 750 did the same thing. The fan started to make a rattling noise one winter and within a short while it would only work on high and then finally the thermal link let go. It was determined that the plastic fan keyway where it slips over the motor shaft had rounded out and was hardly turning and not blowing any air over the resistor.
Being that the fan is a DC motor with a reasonable current draw, the only real inexpensive, practical way to offer speed control is through a power resistor.
 

O'Rattlecan

Redneck Prognosticator
26,687
797
Belton, MO
Does anyone know where they keep this god forsaken resistor? Is anyone familiar with how this truck is laid out?

Should I be worried about fixing all that other nonsense you are talking about Duncan?

Ryan
 

DNFXDLI

The Token Canadian
Staff member
Does anyone know where they keep this god forsaken resistor? Is anyone familiar with how this truck is laid out?

Should I be worried about fixing all that other nonsense you are talking about Duncan?

Ryan

Normally it is located just near where the fan motor is and faces inside the plenum. If you are referring to the thermal link, it is an all in one unit with the resistor...a connector attaches to the pins and two small bolts hold it in place.
Now, this is for a Super Duty.
 

73F100Shortbed

That's how we roll!
5,937
320
NJ
Does anyone know where they keep this god forsaken resistor? Is anyone familiar with how this truck is laid out?

Should I be worried about fixing all that other nonsense you are talking about Duncan?

Ryan

Like Duncan said it should be right near the blower motor which is usually under the dash. And you won't have to worry about the stuff duncan said. He must have had his electrical book out again smilietease
 

DNFXDLI

The Token Canadian
Staff member
I was merely 'splainin why a "module" wouldn't be used to control a DC motor in an automotive application..smilietease :rofl: :rofl:
 

O'Rattlecan

Redneck Prognosticator
26,687
797
Belton, MO
Just to be clear, I wasn't putting down your post. I'm sure it was spot-on and useful. To me, electricity is magic. I understand very little. AC is especially magical. DC makes a *little* sense.

Ryan
 

DNFXDLI

The Token Canadian
Staff member
I knew that Ryan..no worries :D Electricity is magical..especially when it doesn't work right...:rofl: :rofl:
 

blacksnapon

Moderator
Staff member
They actually do have two methods. One, the infamous resistor (still), two, theres a blower motor controller (a module). But, you only have one or the other because they do the same job. I think yours has a resistor behind the glove box.
 

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