97 Sierra Blower Motor Not Working Any Speeds....

ndccpf1 · January 21, 2009

Replaced the Blower Motor Resistor ...no FAN at any swtich setting

Removed FAN and connected both terminals direct to truck battery and

it spun

Tested for voltage at the blower terminals and had 13.5 volts (fan

does not spin when plugged back)

So I have 13.5 volts now at the blower motor leads but FAN not

turning. Fuse of course checks good (25A position #12). Is my only

option left to be the dash dial swtich ?

Supertech64 · January 21, 2009

So you put the meter between the power and ground terminals and got 13.5 and it did not move? If you have battery voltage at the leads at the fan it should be running on high, unless your terminals are melted or loose.

The way I remember that system if you have power at the terminal on the motor your resistor, relay, fuse, and switch are not the problem...I would suspect a ground, but you said that you checked it at the motor terminals.

Could be your motor has just enough resistance to need extra amps to spin because of age or corrosion, so it works with a shorter or larger wire strait to battery.

ndccpf1 · January 22, 2009

Yes I pulled both leads off the motor..turned the swtich on high and put the digital multimeter on + and -. 13.5v was present. Ran a separate hard ground lead today and fan did not spin. I assume I have only the switch and a relay left ? I need to find a schematic to better see how GMC runs the ciircuit. I figure battery=>swtich=>relay=>blower resister=> motor ?

Supertech64 · January 22, 2009

If you have battery voltage and ground at the terminals.... it has to be the motor. You may have a secondary problem if your lower speeds do not work, but battery voltage at high speed means the switch has energized the relay to feed the motor direct current bypassing(thats why the relay is there, to bypass the resistor for high speed) the resistor.

Voltage at the motor means the relay(energizes on high speed only) and switch(powers all lower speeds though resistor and enables high by energizeing relay) are doing their job, and the resistor is irrelevant because you see battery voltage on high and that bypasses it.

Kinda repeated it there but I wanted you to have a good scope on things.

I have a 1998 manual here infront of me and thats the way it looks...but will see if its identical to a 1997 tommarow at work...

ndccpf1 · January 22, 2009

OK thanks. Tomorrow I will tackle the whole thing over as I will have more time to review each part end to end. I will let you know.

ndccpf1 · January 23, 2009

I tested at the motor leads again. 13.5V at all settings except for HIGH and this was 0V (strange). I pulled the dash and jiggled the switch and all started working. I went to local GMC dealer for the $ 29 swtich. All is working fine now. Thanks again !