Blower Motor Stays On!!??

[MPNX2]

Our 1996 Explorer Limited has as issue where the blower motor stays on irregardless of the key being in the vehicle or not. The other night after I got home from work apparently it stayed on and of course drained the battery. I had to use jumper cables in order to power the vehicle up. As soon as power was applied the blower motor instantly came on. The keys were not in the ignition yet. So I pulled the interior 7.5 amp fuse and the blower stayed on, next I pulled the 50 amp fuse under the large fuse box under the hood and the blower stopped. I then located the relay box near the passenger side headlight and it looks like it can house 5 relays but only two were installed (Part #F57B-14B192-AA ) on the left side of the box. I pulled both of these and reinstalled the 50 amp fuse and the blower motor was still on. I assume the next thing to check needs to be the ignition switch under the dash or have I missed something?

 

[J_C]

I thought we had some sort of "battery saver" circuit that would disconnect the battery before accessory power drained it too low?

I don't have a fuse and relay diagram in front of me but basically trace it back starting at the fan, see where a relay is stuck in on position OR the relay coil lead is receiving power when it shouldn't. Sometimes flicking a relay hard with your finger or a screwdriver handle will get it unstuck, or of course swapping with another of same relay on another circuit to see if that changes what is malfunctioning.

 

[BobbyTang]

Theres a circuit the controls the blower motor speed under the dash on the passenger side in my model..

Is that chip board/resistor fried? Smell any burning plastic lately?

Next thought is maybe the mode selector switch is broken and stuck on vent or something.. but I would think it would still power down without a key in the ignition?

 

[J_C]

^ Yes it should still power off with the key out of the ignition.

Whether it has manual or automatic climate control, either way it controls motor speed but if that subcircuit blew out it would not cause the fan to keep running.

There is a blower motor relay in the power distribution box under the hood, and a diagram of it in this thread:
http://www.explorerforum.com/forums/showthread.php?t=180814

 

[mic98xlt]

I take it you have the digital EATC controls. That system is unique and has a electronic type resistor for the fan unit control speeds (blower motor speed control). One side of the blower fan is basically controlled by a hot lead that is switched on (ignition) by a relay when the key is switched on to run. That relay is in under the air cleaner or by the passenger headlight as you mentioned. This is for the direct hot 12volts (50 amp fuse). The other side of the fan gets it's ground potential via the blower control module which can be varied to control the fan speed.

I have heard of others who had crazy control systems problems including heater and fan not shutting off due to the EATC blower control module. I believe the EATC control module some how is creating a "loop feedback" circuit which causes the relay(s) to remain energized although the EATC controls has been physically switched off.

I would try checking the fan motor and cage itself by removing it from the engine compartment to see that it is not binding or dragging and spinning freely. The fan motor dragging can cause premature burnout of the blower control unit. Then physically remove the blower motor control unit (electronic resistor) and examine it for damage to the circuit board. The price varies big time for the blower motor speed control so shop around on EBay or Rock Auto for the best price. Good luck.

 

[J_C]

IF the EATC EDIT: transistor, not the control panel module itself[/EDIT] blew out then there's another topic on the site where I gave a part # to DIY repair it by soldering in a new resistor (the most likely fault on that module). IIRC the cost was around $12 delivered (plus soldering iron, heatsink grease, solder, rivets or bolts + nuts).

http://www.explorerforum.com/forums/showpost.php?p=3278612&postcount=5

 

[mic98xlt]

IF the EATC blew out then there's another topic on the site where I gave a part # to DIY repair it by soldering in a new resistor (the most likely fault on that module). IIRC the cost was around $12 delivered (plus soldering iron, heatsink grease, solder, rivets or bolts + screws).

http://www.explorerforum.com/forums/showpost.php?p=3278612&postcount=5

Great info for the future for me and and it sounds like an easy repair

Here's a link to testing the blower relay if you don't have an extra one to swap it out.

http://easyautodiagnostics.com/misc-index/ford-relay-bench-test-1

I don't believe your relay is bad but it might give you peace of mind. Also by removing the relay you can test to see if the relay is being switched by the ignition. You can get the wiring diagram on an site such as Revbase.com for free so you know which pin is which for power feed and closed circuit for fan operation.

 

[J_C]

heh, I meant solder in a new transistor.

 

[koda2000]

as i think about it, another poster had this problem a few months ago. i don't recall what the resolution was. it could have been the ETAC or it might have been the blower control module. i'm pretty sure it turned out to be the EATC. if i can find it, i'll post a link.

 

[J_C]

The thing is, I wouldn't have expected a blown EATC transistor to cause the fan to stay on... not saying it's not possible, but usually that would either fail open and the fan wouldn't run on speed controlled mode, or would fail shorted and just run the fan at nearly full speed only when it was supposed to be running.

 

[mic98xlt]

This was the most similar post I could find about the blower motor staying on with the EATC. There are many such post with blowers and EATC staying on but this one was the only one I found with a solution. Some did expect it was the EATC unit itself, but I didn't find anyone who found it to be the exact solution.

http://www.explorerforum.com/forums/showthread.php?t=145731

 

[crunchie_frog]

I am having a similar problem on a 2000 with eatc. What I have found in searches is that it it is the blower motor controller that is mounted on the blowe motor housing in the engine compartment. One search revealed you could just try to take it apart and clean it and that will be my first try. If that does not work I will try a junk yard part, clean it and give it a try. They are about $50-$75 for a new one.