Mark III Blower Motor Issues

Bill –

My 71 Mark lll with automatic climate control has the next problem. Blower motor doesn’t work at all. No matter where I put the slide switches. Motor works with the positive direct from the battery. When I measure with a multimeter on the two wires there is 12 volt. Where should I start looking.?

Ps I’m not very good with electric – I do have the Factory Shop Manual

Martin

Hi Martin –

These controls are complicated but even If you are “not very good with electric”, you may possibly be able to check a few items.

In your information where you tested the blower motor you say that the blower does not operate in any position of the controls and that the two wires have 12 volts. What two wires are you referring to? and what are their colors. Did this problem possibly begin after some sort of repair to this car or? Let us know this and any other information that may help us to give you any advice at all.

Sincerely,

Bill

Bill –

I’m talking about the 2 wires that go to the blower motor. Orange and a black one.
With a multimeter there is 12 volt. A control lamp doesn’t turn on. There where no any repairs lately. I don’t know if the blower motor worked when I bought the car 2 years ago because I normally only drive her in nice weather.

I have looked under the dash at the passenger side. There was one orange wire hanging around. black stripe wire to the blower motor feed wire and then power exits the motor to the Can’t see where it should go. Send you a picture.

Martin

Hi Martin –

You have said that the blower operates when you apply direct battery power to it. The 1971 wiring diagram shows the two wires that connect to the blower motor, an orange one with a black stripe and a black one. The ATC controls apply power to the orange /
black wire and then to ground and the motor turns on. So, the orange wire {if it has power as you have said} is connected to the motor and the black wire is in fact properly grounded, the motor must operate if it is has already been tested and proven to be o/k with direct power from the battery.

Do your Power Windows operate?

Sincerely,

Bill

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Bill –

Power Windows work fine. Atleast in the doors.

Rears don’t work.

The black wire on the motor is OK, because when I only use the plus from the battery,  the motor works.

On the orange/black wire is 12 volt but no amperage. 

Martin

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Hi Martin –

Try this. With the engine running set your control on DEICE. This position should lock the ATC on high blower speed and full defrost. The orange wire should then receive battery power and the blower should operate. If the blower operates properly at this time but will not operate in the lower normal automatic speeds in the other control positions, some other ATC component unit must be at fault or the blower motor is seizing or drawing too much power and is faulty. I cannot determine any of this from here and I trust that you have checked out the ATC circuit breakers and fuses etc. as shown in your manual. Any other suspected components then would need to be removed and inspected. Read your manual carefully to be clear how the system operates. It is a complicated system but it works very well when it is operating as designed. 

Sincerely,

Bill