Interior fan speed only working on high

[CrapaTaurusWrecks]

For some unknown reason that I'd like to try to figure out my interior fan (blower motor) only works on the high speed. If I have the A/C, heat or just the fan on it has to be on high or it doesn't work.
Anyone have any ideas on how to fix this?
2001 SE with a Vulcan if that helps any.

TaurusGLenn

[tripletdaddy]

Assuming you have manual controls for temp, setting and blower speed, there are basically two things that would be your problem. Typically, a bad or burned out blower motor resistor assembly will give you just high speed, but the fan speed switch could do that too but not as likely. The resistor set is typically screwed to the near bottom side of the hvac plenum "box" below and near the glove box.

If you have the electronic, electronically controlled sytem, the blower motor speed controller is bad. Not sure if that is actually the same exact part as the resistors as witht he manual system. Maybe a wire came loose from being bumped loose, but not likely.

[way2old]

Maybe this will help.

Blower Motor Resistor
Removal and Installation

Remove the right-side instrument panel insulator.

Remove the blower motor resistor.
Disconnect the electrical connector.
Remove the screws.
Remove the blower motor resistor.

To install, reverse the removal procedure.

[shorod]

Originally Posted by tripletdaddy

If you have the electronic, electronically controlled sytem, the blower motor speed controller is bad. Not sure if that is actually the same exact part as the resistors as witht he manual system. Maybe a wire came loose from being bumped loose, but not likely.

Agreed that the blower motor resistor is the likely problem. There is a "high speed fan relay" that bypasses the resistor block for high speed, which is why the blower will work only on high speed when the resistor block fails.

If the car has the electronic automatic temperature control, then they use a solid-state blower motor controller that uses Pulse Width Modulation (PWM) and a transistor to vary the fan speed on speeds less than high. Earlier years had problems with moisture getting through the conformal coating causing the electronics to fail. I haven't read of this being a problem after the 1996 or so model year. These solid state PWM controllers are expensive, so you'll want to be sure it's the problem before replacing it. They are usually located in essentially the same location as the standard resistor block.

-Rod

[CrapaTaurusWrecks]

[quote=tripletdaddy]Assuming you have manual controls for temp, setting and blower speed, there are basically two things that would be your problem.
Typically, a bad or burned out blower motor resistor assembly will give you just high speed.
Yes, I have manual controls. Is there a way to check to see if the resistor assembly is bad?
Thanks, that is some quality advise from all of you!

TaurusGLenn

[shorod]

Once you find the resistor block, unplug it. Then, get out your multimeter, set it to the "Ohms" scale and check for resistance between the terminal in terminal location 2 (corresponding to orange/black wire of the connector) and the terminal at terminal 3 (corresponding to black wire of the connector). These are the terminals of the resistor block, not the wires in the connector. There should be some form of resistance here, but if read open circuit (or OL on some meters) then the block is bad.

-Rod

[davek4699]

This page was helpful to me. When I found and removed the resistor assembly, I went to Radio Shack and bought just the "Thermal Resistor" of the right temperature. Be careful though, I did not read the directions and I "soldered" the new one in=and da= I burned it out. So the second one I curled the leads and drilled a small hole and screwed it into place. You also could solder it using a plier or clamp to divert the heat. The fuse cost less than $2 and was a lot cheaper than buying the whole unit. dave