what would the truck do if the fan resistor was bad? would the fan stay on after the hvac controlls were off?

 

Some of the fan speeds would not work.

 

There is also a thermal fuse in the fan resistor .The fan would not run at all.

 

there is only 2 speeds working now.....medium and high......

then when i shut the heater controls off, the air routes to the defroster and blows out high when the truck is running and when it is in the ACC postion....

 

forgot to mention this is the EATC resistor, not the stock 1....

 

The highest speed completely bypasses the resistor assembly. A resistor problem would have no effect on the highest speed.

 

That is not the same thing. It is a fan speed controller module. I had one fail and it defaulted to the highest speed as it says in John's How-to. There may be other possible failure modes.

 

so even if the control head is off, it will still blow air? that is what it is doing now.....and i have 2 speeds in the unit......

should i order a new unit tomorrow?

 

That is a variable speed controller, not one with discreet steps like medium or high. Of course, the blower should be off when the HU is off. I suspect that you have a wiring problem but I'm here and the truck is there, so I can't say for sure. I wouldn't order the FSC until you know it's bad - from what I've heard, it isn't cheap.



EDIT: I went back through the How-to and found this:

The "key-on" method that John is describing is where you do not add a relay and I believe this is how you did yours. So, it could very well be the FSC has failed. Now that I reflect on it, I think that mine did run continuously with the key on after the FSC failed. However, I don't remember for sure because it was only like that for a couple of hours before I could get a used replacement FSC. It makes sense though and John knows more about this mod than anyone.

 

the O/BLK wire goes to the B/O wire at the FSC, and to the B/O wire at the HU...........i am assuming that it doesn't go any were else under the dash....

 

the only relay i have is so the "rear fan off" switch shuts the a/c compressor off.......that has the 2 PU wires (1 from the HU and 1 from the trucks harness), 1 of the R/O wires from the head unit and a switched 12v wire

 

You did it the same way I did and you didn't install the extra "optional" relay for the blower. Assuming that the FSC has failed, that is probably why the blower is running all the time with the key on. Why there appears to be a medium and a high speed is a mystery to me though.

 

i tried installing the 2nd relay, but nothing worked then.....the only way i could get it to work at all is by using the single relay for the "rear fan off" switch..........then i had to put the Y/BLK on a R/O wire that was in the trucks harness from the factory.....

i am going to order a new FSC tomorrow, hopefully it will be here by Friday and i can install it and see if that fixes the problem.....

 

a Ford dealer near me has 1 for an EATC in stock....can't believe that

i am going to go get it at lunch....he said it is only $69.56 + tax.....that isn't bad at all!