Fresh Air Blower

[DanMan68]

I have a '77 that I just replaced the fresh air blower in. Old one was worn out, and barely spinning. Due to some other work I was doing to the car, I had the complete front HVAC system out of the car, and just re-installed it with new ducts. Unfortunately, now the motor does not run at all...

Fuse looks OK, has anyone had a similar issue? Could it be the control panel? Hooked up the motor backwards?

[wrxnofx]

The plug from the harness only goes on one way, so you couldn't have installed that backwards. Internally, if you swapped the wires when connecting the new blower motor it would simply rotate backwards.

You need to isolate the circuit to figure out the problem. First determine if the problem is the blower motor/housing terminals or if it's the harness leading to the motor/housing.

You should be able to take a 9 volt battery to the terminals that the harness connects to and see if it spins. There are 4 terminals, 1 is power from the fuse, the other 3 are for the different speeds coming from the switch). So put the battery positive on the terminal that is supposed to be hot and put the battery ground on any of the other 3 terminals. If it does spin this way, you've just isolated the problem to the harness/switch side. If the motor doesn't spin this way, then you've isolated the problem to the motor/housing/terminals.

To test the harness side, take a test light to the harness-side connector and check the terminals for power and grounds. If power is verified at the one terminal, turn the motor on from the dashboard switch and check for grounds at the various terminals. Looking at a wiring diagram, if the key is in accessory or run position, you should be getting power to the fuse and therefore to the one terminal on the harness. The switch actually creates the ground and completes the circuit. So if you turn the switch to position 1, that grounds one of terminals to the motor. Switching to position 2 grounds a different terminal to the motor, and so on. There is a resistor pack (in the blower housing if memory serves) that causes the motor to turn at different speeds. If you get no ground at any of the harness terminals, check that the blower switch itself is connected to ground.

[DanMan68]

Thank you! I will give that a try.

[DanMan68]

So the motor does run when jumpered directly to the battery. Will have to start troubleshooting the harness next.

[harv666]

If the engine heater blower mower is not hooked up properly or dead the front blower motor wont run either. And vice versa I believe.

[pete3799]

Check the dash slider. Contacts may need cleaning.

[DanMan68]

Originally Posted by pete3799

Check the dash slider. Contacts may need cleaning.

This is what it ended up being! Cleaned with some fine sand paper and Deoxit spray and it's working perfectly.