HELP.....blower will not stop

[KNIGHTRIDER]

Help with A/C , i have read the MM.net forums on A/C and i am still lost, my problem is my A/C blower will not stop blowing, even after i turn the A/C off. right now i have it unpluged, what could it be?

[CKMustangCobra]

Whatever controls the blower.

Take a test light to the blower lead and while it's lit, yank the A/C controler fuse. If it goes out... you need that assembly.

If not.... start yanking more fuses until you find it.

[blackhueys]

when you say it still blows (lol) is like the blower is on high all the time? Most cars the blower is always blowing some and I may be wrong I can check tomorrow but I think our cars are always on a little bit.

[Motorhead350]

I'm guessing it is the A/C head unit. The whole control that's inside the car that you set the fan and temperature with. Mine wouldn't heat or A/C at one point, just air. I changed it and it's fine now. That could be it!

[Wires]

See this thread for my replies and advice.

http://mercurymarauder.net/forums/showthread.php?t=43165

[Vortech347]

The Blower control module. My guess is that its stuck on.

The HVAC control unit dosn't get power unless the car is on...

[KNIGHTRIDER]

Ok so far i have tested everything except the Blower control Unit. How do i test this? I have steering wheel control and i hear the blend door open and close.

[Wires]

See my link above - the easiest way to test it is to substitute another one.

Disconnect the wiring harness from the old module without removing it, then plug in a new module. (See my link above for Ford Part number) If your motor stops, then you've found your problem.

If not, you still have a module for when yours does go out.

The fan is fed 12 volts directly. (I forget if it's constant or ign controlled) The fan is grounded through this module. The module completed the ground connection with a Field Effect Transistor. For anything but full speed, the FET is switched ON and OFF quickly. By varying the on and off time (called duty cycle) the fan speed is controlled) This is pulse width modulation, controlled by the AC "head unit" mounted in your dash.

There is a relay in the module that bypasses the FET for high speed operation - it grounds the fan directly when the relay is switched by the head unit.

If the problem is a bad module, the FET is shorted or the relay is stuck on. If it's the head unit, then the signal to the high speed relay is constantly on.

As someone said, if the fan continues to run with the head unit off, chances are it's the module.

Mine was the opposite condition - open. (No fan) I did smell a burning smell before it went out.

I'd like to examine a bad "shorted" module, to see if it is the relay or FET that fails. I had a theory a while ago that a FET with a higher rating was needed, but I have yet to prove this by seeing any modules with a shorted FET.

Sorry for the diatribe, there.