Hi, This has to be the weirdest problem I have ever run into.
To start off, I started loosing heater blower speeds over time (approx 1 year). First I lost low speed, then 2nd, then 3rd, and recently 4th (or HI speed). I suspected that the blower resistor had finally gone, so I purchased a new one and replaced it. No change in fan speed. I then suspected the fan may be the trouble, so I removed it, and connected it directly to a separate car battery. The fan ran perfectly like it was on high speed. I then checked the voltage at the power plug that connects to the fan. It had 12.47 volts. With the resistor still in place I checked the voltage at the plug through all 4 speeds. there was 12.4 volts on all 4 speeds. Now I was stumped. I got into the driver seat and started the truck, and here is the weird part. If the blower mode selector is in any position (Floor, Window Defrost, Etc.) other than OFF, I cannot take the tranny out of park. Once I set the mode selector to OFF, I can then take the tranny out of park. Also, with the fan sitting on the floor and connected, the fan does turn really slowly, maybe 50 rpm.

Any ideas ?

Cheers,
TT

 

Sounds like corroded grounds. Weak ground path makes for funny operations , Check your passenger side kick panel .

 

Thanks for the advice. I will look into that a bit deeper

 

Hello again.
I checked around the fuse box area, but could not see anything that looked like a corroded connection. I hooked up my ODB scanner to see if any codes would show up. There wasn't any. But another weird thing happened. When the scanner was connected the problem went away. Everything worked as normal. The fan had all 4 speeds, and I could shift the tranny if the mode selector was in any position. As soon as I disconnected the scanner the problem came right back.

Does this bring any new ideas about the problem ?

Thanks,
TT

 

Still sounds like a ground issue to me.

 

I agree with the others that it sounds like a ground problem. Looking at a 2004 F150 wiring diagram, the blower motor's ground is G203. It's located below the fuse box. A lot of F150 owners have found that ground to be rusted. I think you have to remove the plastic panel below the fuse box to see it, and the plastic sill plate must be removed first.

Good luck.

 

Mice eating the cables?

 

Hi,
Thanks for the advice with this fan issue You guys were totally right about the ground being the problem.
I found the ground connection to the frame just below the fuse panel. It looked really rusty in that area.
I grabbed the wire and pulled on it lightly and a whole chunk of the frame separated away with the wires. It was totally just a pure hunk of rust. No actual metal left at all.

I cut the end of the wires (there were 3 at that junction. One bigger wire for the fan, and 2 smaller ones for something else. Not sure if they had something to do with the fan)
I crimped new ends and screw drilled them farther up the frame where there was no rust, and covered the area with dielectric grease to protect from further rust.

It solved the problem right away.
Thanks again
TT.
PS: Does anyone have a diagram of the multiple ground locations. It is 2005 F150 FX4 model. I'm sure with the amount of rust in this truck, I will be in trouble again soon with something else.

 

This is for a late model 2004, and I think the 2005 is the same.

 

Hi,
That's great. Thanks for the reply.
TT