Blower motor quit

[jay6891]

My heater blower motor just quit. Thought I blew a fuse. Checked it out everything ok. Unplugged the wire going to the blower and showing 14.7 volts with engine running and blower switch on high. Thought the motor finally burnt up. Just to be sure I hooked a temp wire from + side of battery to motor and the thing works. Now if I hook up the real wire to the fan and put a multimeter on it the reading is 0, if I unhook the wire and test again 14.7. I'm lost, any ideas.

[CraigS]

Look to see if your resistor pack is bad. I don't remember if the motor is switched on the ground side or the power side.

[jay6891]

I checked the resister (sp), voltage goes up as I come up on fan speeds. I'm pretty sure it is + switched. Will probably go get a fan motor but trying to figure out why it works when wired direct and wipes out all my voltage when plugged up through the factory harness.

[crazyred]

yepper, sounds like the resistor pack .... just a *note* i do believe that there is a fuse in that resistor pack for low and for Medium, high speed is just straight supply power and has a NO resistor and therefore connected after fuse in the resistor pack. i'd suggest to replace the pack and all should be good .... but if she craps out again well then you need to look at the blower motor. It's got too much fricton to turn freely and is therefore drawing too many amps and blowing the small fuse in the pack.

[GMC Jim]

according to the wiring diagram I have; the 'high' speed blower motor switch setting goes thru a relay. This relay is located on the inside of cab, right side, up alongside the glove compartment box............ Jim

[Billla]

I have a blower that runs, but on low only. I was planning on replacing the switch just as a "let's replace this and see what happens" thing...should I be looking at the resistor pack and/or relay instead?

I'm definitely not an auto electric whiz

[CraigS]

Jay6891 - it's definitely not the motor if you can get it to run direct wired.
Billa - if you have low speed, you're resistor pack is OK. I'd check the switch/switch wiring.
GMCJim - are you sure you have the right year diagram? I have a 72GMC with no relay on the firewall. It's direct wired thru the switch on mine.

[GMC Jim]

Craig S.... My '71 GMC with factory air does have the relay ( I have replaced it!) Looks like trucks without air did not use the relay.... Also the standard fan used with heater only trucks draws 6.25 amps max ( 2550 - 2950 RPM).
The standard blower motor used with factory air draws 16.5 amps max ( 3700 RPM ) . Recalling previous messages regarding heater/air blower switch malfunctions; it appears that if the heavy duty ( air-cond) blower is used with the heater only installations, the amperage could damage the blower switch unless a relay was installed for the 'high' blower function. ( just my 2 cents ! ).............. Jim

[Tx Firefighter]

I've seen before, where a switch will pass enough current to light a test light or show full voltage, but not enough amperage to work the fan.

Jumper the switch itself and I bet you'l find the motor runs.

[jay6891]

I was thinking of that today at work today Tx Firefighter. Took the switch apart and cleaned it and polished up the copper contacts. Not much to the switch though gotta love 1968 tech. Still same result. Anybody know which fuse it is in the fuse box. Can't read the writing anymore. Maybe losing the amperage in the fuse box contacts.