blower motor, only speed 4

[chengny]

Was it really rusty/oxidized or just kind of dusty?

As you know, other than the ground lead from the blower motor casing to the firewall, that purple wire is the main (and only) conductor supplying the blower.

Jump around it and try running the blower up and down.

If that doesn't do it - make sure you check the ground connections (the fan and the relay both) for continuity to the firewall. Do it with a meter.

 

[flyboy1100]

Grounds checked and cleaned already. Purple wire ( and rest ) are green and corroded

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[flyboy1100]

My new connectors don't quite fit, but that doesn't appear to be the problem will see of I can trace wires tomorrow

I do have 12v at red, blue, orange wires always and purple if on 4.

Kinda suspecting the motor itself at this point

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[flyboy1100]

Learned invaluable lesson tonight.... Don't accidentally short out relay.... Uhhh going to junkyard's tomorrow to hopefully find a relay harness I can splice in.

I did buy a new motor and it didn't fix the problem unfortunately. I think the problem does lie in the relay harness since I could wiggle the wires a bit and speeds other than 4 kinda worked. Time to dig out wiring diagram

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[chengny]

Yeah, I was going to say your relay is shot. I had written and saved this, with the intention of posting, but had to crash for a few hours:

I do have 12v at red, blue, orange wires always and purple if on 4.


That's wrong, they should not all be at battery voltage:

Red should - it's fed straight from the battery (via the firewall junction block) and supplies the relay's control coil

Purple can - but only when high is selected. This wire is the output from the relay to the fan. When blower speed switch is not set to high, it will show three different voltages:

1. About 9 VDC - for medium speed operation
2. About 6 VDC - for low speed operation
3. 0 VDC - when the fan switch is turned to OFF (all the way to the bottom)

Orange should - that is full 12VDC from the blower switch into the relay and by-passes the resistor stack. It is connected to the purple within the relay when the switch is on HIGH.

Dark blue should not - ever- that is the variable (reduced voltage) feed from the resistor stack. It should show either 9 or 6 volts depending on whether Low or MED is selected at the switch.

I think your resistor pack is shorted.

Here is a good dwg - it's probably the clearest wiring diagram of the HVAC system I have ever seen. You can actually see inside the switches, resistor stack and relay (the relay section is incomplete):

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BTW - The fan speed switch used in GMC trucks of this era has 4 positions. All the wiring diagrams show those positions as (from the top down):

High
Med1
Med2
Low

But they are not that way. Unlike say a Ford truck, C/K truck fans can be completely shut down. The actual blower speeds are (from the top down):

High
Med
Low
Off

 

[flyboy1100]

hmm, it is a new relay, i can take it back and get another. would have saved me a lot of trouble if that is what it is. it is one of the first things i replaced too

i did get a new harness i need to splice in this weekend from the junkyard today!

 

[flyboy1100]

Stupid relay, first thing I replaced, was bad! I didn't need to replace the rest. I hate getting defective parts

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[89Suburban]

So is it fixed?

 

[flyboy1100]

Yes. Annoyed I spent 65 more then needed because the first thing I replaced was defective. Oh well

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