a/c blower on high

[thh]

My 99 explorer (Eddie Bauer) is running the ac system at high only. Entire a/c & heat system will not turn off either. Since this is an Eddie Bauer, it has the automatic temperature control system (atc) in it. When I first got it back in November I had a similar problem which I fixed with a new atc resister module. The difference is in the previous issue I could shut the system off or use either high speed or blower completely off. The dash fan switch is bad and recently the fan button on the steering wheel had started acting up as well (when pushing the switch for lower speed it would sometimes increase speed instead). Other than that it has been working well. Any thoughts ? Car is 4 liter sohc with 211,000 miles.

 

[mic98xlt]

Just today I replaced the blower fan and blower resistor on my '97 Mountaineer with manual heater controls.
I realize yours is an ATC but the electronic principles I believe are pretty much the same. About 2 years ago I changed out the blower motor fan with an new aftermarket replacement one from Advanced Auto. It worked fine until this spring when I noticed the fan motor would only work on high speed. I then did a little reading here and determined the blower resistor for the lower speeds was bad so I changed to an aftermarket resistor. I put in the new resistor and the lower speeds did work. Within a week the lower speeds stopped again with the same problem. I had noticed the connector for the blower resistor had a little rust so I replaced the connector. It still didn't work with a new connector so I checked all the wiring (also control relays under hood) including the fan switch on the heater controls on the dash. Nothing was found so I assumed the blower resistor was good since it was only a couple weeks long. The fan motor outward appeared fine and it worked on high speed so I assumed it was good.
Because another new fan resistor was cheap ($20), I brought a new Motorcraft one. Since it in the same area housing as the fan, I decided to also swap out the fan motor with a used Motorcraft OEM I had lying around. Upon taking out the aftermarket fan, I sprung it by hand and it just barely turned. The motor was bad and apparently too stiff to accommodate the heavier current (amperage) required by the blower circuit on the lower fan speeds that are controlled by the path on the blower resistor circuit. I replaced the fan blower with the used Motorcraft and a new Motorcraft Blower resistor and all is definitely fine. Off and on, I have spent some 6-7 hours chasing this problem and it all could had been avoided if I had first physically checked the fan blower motor to see that it was spinning freely.
I believe your fan motor bad, probably drawing too much current which is causing the resistor module to burn out or causing "Gremlins" in the heater fan circuit. I made some bad assumptions about the blower resistor being good (2 weeks old) and should had known that something was causing my fan resistor to go bad early when the blower symptoms returned too soon.
Good Luck