2000 Mercury Grand Marquis. Heater blower stopped working. The blower motor control module is probally bad but son does not have money to replace it. The EATC is OK. Can I go out to the blower motor and tap into the wires and run a new resistant switch into car and bypass the blower motor control module. When car is running you can turn on heat and place on defrost and you can feel warm air coming out just no blower to blow it out.

 

It is possible to do what you ask, but make sure you disconnect any wires going to the motor first. Then if you run a wire from a hot source with a circuit breaker or fuse in the supply wire to the motor all you need to do is place a good heavy duty switch in the other wire to the motor which will be the ground wire. Those motors pull a lot of current and make sure you use a good heavy gauge wire for both wires. I believe they protect the circuit with a 30 amp fuse. You can try your idea before running any semi-permanent wiring and see if the motor runs at all . The problem may be the motor itself.

 

Hanky is right - first make sure that the motor is working. Once you proved that, you can buy a PWM controller like the one shown below, connect its inputs to the battery via a 30A fuse, and connect the blower motor to its output. This has the advantage of letting you adjust the motor speed ... so you won't have it full speed (and full noise ) or nothing ...

QKits Electronic Kits: MXA066, PWM DC Motor Speed Control 30 A

If you choose to go with the (simpler and more practical) switch approach suggested by Hanky, it is always good practice to have the switch between the fuse and the blower, so that when you open the switch, no hot parts are left downstream from it, and the fuse also protects against any wiring shorts. So your made-up blower circuit should be "battery +12V" > fuse > switch > blower motor > ground.

HTH ... good luck!

 

I like your recommendation with the PWM unit cougar_fan ! It will most likely be even better than the original set up. Thanks for the good info. Glad to see your back.
Mr Lawson will have a deluxe heater fan control if he decides to use it. Hoping everyone has a Happy Thanksgiving.

 

One other thing to think of: heat. These cars without EATC had the old wire-wound blower resistors mounted in the airbox to the passenger compartment to get rid of the heat created by the voltage drop (it turns the extra voltage availible in the car, but not needed or wanted at the blower into heat). Just keep it in mind. I don't want to hear how the car burned to the ground!

 

Greasemark , you brought up a good point.
If the present wires going to the motor are disconnected from the motor , the circuit is incomplete and the resistors are non functional. The blower speed is controlled entirely by the PWM unit that would be wired directly to the motor. What is your opinion on this cougar_fan?

 

You're absolutely right, Hanky, those resistors are switched in series with the motor to reduce the current fed to it (and slow it down) - but the PWM or direct battery connection shoud not include them in the circuit, so there's nothing to worry about.

EATC is actually using a PWM controller to modulate the fan speed, and there's a great chance that this unit is faulty on your car, preventing the blower from working. A car equipped with EATC should not need (or even have) these series resistors, unless it is an early model, made when PWM controllers were not reliable enough to deploy in a car, so the fan speed would have been controlled with relays connecting the blower resistors in series with the motor, in steps, to control the speed.

Your blower motor should have two wires coming out of it. Disconnect them from the car and connect them to a 12V battery (polarity is not important at this step, as these DC motors can spin in both directions). If the fan spins up (and the blower's fuse in the fuse panel is good), then the EATC electronics are toasted - so go for the switch or PWM controller approach. If the blower doesn't spin, then its motor is toasted - replace the thing and hope that the EATC did not go bad as well

If the blower works and you re-wire it with a switch or PWM controller, connect the motor one way and test it. If there's very little or no air coming out of the vents, you powered it the wrong way, just revert the wires at the PWM output.

One more thing: PWM stands for pulse width modulation. This means that the controller is "pulsing" the motor to make it spin slower. The wider the pulses, the longer is power applied to the motor, so the faster it spins. However, the pulses come at a constant rate (above 60Hz, usually between 400Hz and 2kHz) so you may actually hear a humming coming out of the motor when you reduce the speed. This is perfectly normal, you don't have to worry about it.

Let us know how it goes. Good luck!

 

cut the wires from the blower, ran new wire to postive + to 12 volt with fuse in between to a postive acces. so only has power when key is on. ran ground - to battery ground. we talked about a switch and son son just put in a toggle switch which will run the blower on high when ever on. Later when we have more time then order and get the switch you guys talked about. weather turning with rain and cold maybe some snow he just wanted something now that would work. after hooked everything up works great air, heat, defrost can still adjust temp control just blower on high which is ok for now. he said if he got to hot he could roll down the window or flip it off but at least he now has heat and a defroster. thanks for everything guys.

 

As I stated previously , those motors pull a lot of current.Just make sure you used a heavy gauge wire . If you used a 30amp fuse with wire that is rated for a 20 gauge fuse the wire could get overheated and cook before it would blow the fuse. These are little things you need to be aware of. Stay warm !