fan controller stuck on high speed only

I have a 2014 and the fan only works on high. I changed the resister and it worked great for about 3 weeks then went back to the same problem. Is there something else I can do? thanks - Dave

Hi @davjoy ,

Here's a link to the 2011-2014 Ford F-150 Workshop Manual + BRM scroll down to Climate Control System >Climate Control System – General Information and Diagnostics to view the section of the manual dealing with the blower motor resistor etc.

On p.194/239 (file page number as the numbering in the manual is hard to follow - check the page number box top left of the header bar) it says "Check the blower motor and blower motor cover (if equipped) for moisture resulting for moisture bypassing the cowl baffling system...."

I know it says that it is in relation to odours in the A/C system but any moisture in the blower motor area and if that is where the HVAC control module also is (I'm not sure) it may not be that good for it. Perhaps if there is moisture or corrosion across the connections it may be shorting them out

On p.184 it shows how to test the resistors in the resistor unit. If you still have the old resistor units (both of them) you may be able to find out which resistor (or if all of them) are burning out and then check out the HVAC module connections for any corrosion etc (see Electrical Distribution > Module Communications Network section of the manual).

Altering the fan speed changes the value of the resistors in the circuit and this signals the HVAC control module which then regulates the blower motor speed. It is a two step process basically operate speed switch changes total resistor value in circuit by connecting them different ways using the speed switch which is detected by control module which then alters motor speed. In the old days (showing my age) the resistors themselves altered the motor speed as they were connected directly to the motor circuit and didn't have a control module in between.

Life was simpler before electronics got into cars ;-)