Hey guys i have searched until i am blue in the face and haven't found an answer. I just picked up a 99 Navigator with the automatic temp controls with the thumb wheel for fan speed control. The fan is blowing on high all the time (speed controller?) but i can still select where it blows (floor, vent, defrost, etc) and it changes. The problem is, that if i push the OFF button on the EATC, the display shuts off yet the blower stays blowing on high and switches to blowing out the defrost. I have tried the self test on the EATC and get all 888 with no codes. So do i replace the EATC, the speed controller or what? Thanks for the help. Also, will any EATC work or will it have to be from a Navigator or Expediton?

 

Replace the speed resistor.

 

95% probability that it's the blower speed control module. Shorted transistor, probably.