Blower Motor will not turnoff with EATC off button | Ford Explorer Forums - Serious Explorations

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Blower Motor will not turnoff with EATC off button

rjmorrow

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August 15, 2011
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City, State
Limestone, TN
Year, Model & Trim Level
1998 Ford Explorer
I have a 1998 Ford Explorer Eddie Bauer 5.0 that the blower motor will not turn off when pressing the "Off" button on the EATC. I've replaced the blower relay in the power distribution box. Could the problem be with the blower motor resistor?
 



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Yes, a common problem, I have two vehicles with EATC and had to replace them both. You can try taking the speed control resistor module apart and cleaning it which I did and it worked for a while but I ended up having to buy a new one. The part runs from ~$45 to $75.
 






That's probably a leaky, or shorted-closed transistor. It could be a transistor in the head unit in the dash, or the main power transistor in the firewall module that people call a "blower motor resistor". Since the firewall module is more likely to fail, shorter lived, I'd suspect it more.

There's a topic or two on this forum were I posted a link to a replacement transistor for about $12 delivered if you're good at soldering.
http://www.explorerforum.com/forums/showpost.php?p=3278612&postcount=5

If you want the scientific method of discriminating between the two, that firewall module transistor has a base, emitter and collector pin. The drive current (voltage measurement) to it should be zero or nearly so on the base pin (between it and ground) when the head unit is set to off.

The other two pins, one would be at near battery voltage and the other significantly higher than zero going to the fan. If the base pin has significant voltage when head unit is off, that's a sign the head unit has a problem. If it doesn't then the firewall module is bad. You don't necessarily need to figure out which pin is which, just that one of the three should have near zero voltage (between it and any chassis or battery ground) if the head unit is working right and set to have the fan off.
 






A few years ago my blower only worked on high regardless of speed selected when heat or A/C was on. Fan did not blow if EATC was off. I changed the control module at the fan and all was well. Now the fan blows at high all the time the ignition is switched on regardless of if EATC is on or off. Should I assume the replacement module has gone bad or could the fan switch on the control head be bad? The new control module is only 2 or 3 years old.
96 EB 5.0
 






firepop5 you should do the same multimeter test I described previously. If the fan didn't work at all when it should then there are other variables like a blown fuse or relay, wiring or connector problem, etc. but when it does work but shouldn't or should run slower, then you need to determine if the head unit is giving the right output to the firewall module.

There may be another way to figure this out but I am not familiar with the rest of the EATC head unit's circuitry. Disassembling it and reverse engineering that circuit could provide clues but unless you were attempting to do a discrete electronic component level repair of it, first it would be better to see if the output to the firewall module looks right.
 






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