Blower running when off

[tysmith14]

What would cause my heat or ac blower to kick off and on even though it is not even turned on?

Thanks

[alex boss]

Your blower motor relay is malfunctioning. Go into the relay/fuse box under the hood and locate the blower motor relay by reading the inside of the cover. The relay may be very hot to the touch and that is one clue to the problem. Replace it and you should be good to go.

[tysmith14]

Thanks for the response. could it be by chance the blower resistor assembly you think?

[alex boss]

No. Look at the relay. Resistor probs will cause no operation of fans, except possibly on high, which is the default.

[tysmith14]

ALex:
I replaced the relay and guess what, still have the problem. Blowing when it is turned off. Next????????

[Selectron]

What year is the truck? Let me know, and I'll see if I can find a wiring diagram. The typical Ford blower motor circuit runs like this:

Circuit breaker - to motor positive terminal - then motor negative terminal - to resistor pack - to speed selector switch - to ground.

If your truck follows the usual arrangement then the only things that can cause your problem are:

1. Faulty switch (internal short-circuit).
2. Faulty (short-circuit) wiring anywhere along the path between motor negative terminal and ground.

[tysmith14]

It is a 2003 electronic temp controls if that matters.

Thanks again!

[Selectron]

Ah, that does indeed make a big difference. The blower motor for the models with manual A/C and heating controls is, predictably, configured as I described above, and it would be a simple matter to diagnose a fault. The electronically-controlled system is something different entirely - it's a ridiculously complex circuit and to be honest, fault-finding on it would be outside the scope of most home mechanics. If you want to take a look at the wiring diagram for it, I'll put the link below, but it really won't help you much because the system overall is controlled by something called an Electronic Automatic Temperature Control (EATC ) Module, which will be a sealed electronic control unit. The blower motor is shown as being controlled by a Front Blower Motor Speed Controller, which again will be a sealed electronic control unit. Multiple sensors feed into the EATC, and multiple control signals emanate from it - it really is quite a complex system.

In terms of simple checks, about all that you can do is check that the connector on the EATC is firmly attached, and that the unit itself is securely mounted, and also do likewise for the Front Blower Motor Speed Controller.

Any further checks would require a multimeter, to check the voltage feeds and ground connections for both control units, but that could be a fruitless exercise if one of the units has developed an internal fault. I'm an electronics engineer by profession and to be honest, I wouldn't really want to find myself working on this circuit within the confines of a vehicle interior - I think it's plain silly of the manufacturers to even install circuits of this complexity into a car or truck - give me a good old-fashioned manual system every time, with just a blower motor, resistor pack and a switch - not much to go wrong, and easy to fix when it does.

If you want to take a look at the wiring diagram, go to the thread below, follow the instructions in the first post, choose your year and model (it's the same circuit for all models, by the way) and then click on Wiring Diagrams - then Air Conditioning - then Automatic A/C Circuit.

If you have a multimeter and the time and patience to pursue it further then I'll help as far as I can, so just let me know if you want to do that.

And the link: http://www.automotiveforums.com/vbul...d.php?t=890909


Edit: You didn't say if the system works normally at other times - if it does then you can assume the fuses are ok, but if not then it would be worth checking them:

Fuse 2 - 5A, in Central Junction Box - powers the EATC Module.

Fuse 24 - 10A, in Central Junction Box - provides power to the EATC Module, also powers the Blower Motor Relay coil.

Fuse 105 - 40A, in Battery Junction Box - provides power for the Front Blower Motor Speed Controller, via the Blower Motor Relay switched contacts.

Fuse 23 - 15A, in Battery Junction Box - provides power for the A/C Clutch Relay coil.

Fuse 13 - 15A, in Battery Junction Box - provides power for the A/C Clutch Field Coil, via the A/C Clutch Relay switched contacts.

[tysmith14]

Selectron:

I took it to ford and they said it was most likely this electronic thing $50. They wanted another $200 to put it in. I said I will do it myself and save on labor. PUlled out the glove box and it was right there. One bolt and a plug. So far so good. I think this part is similar to a resistor but for the ETOC.

Thanks again!

[Selectron]

That's good - thanks for letting us know. That sounds like the Front Blower Motor Speed Controller - I'm sure the information will prove useful to somebody else in the future.