Lost blower motor and no AC/ Compressor

[miket007]

78 C10 small block with ac...working perfectly for the last 4 years....today nothing.

Fan speed switch does nothing....slide the selector lever over to def or AC...no compressor. Checked fuses inside by drivers kick...all fine. Checked for voltage at blower when it should be on...nothing. Resistor in heater core locks solid with no breaks...checked there for voltage...nothing.

Is this a blower switch or is it the switch connected to the selection lever? I pulled that piece out and apart and all looks good...nothing burned/black or broken.

What else would cause both to cease functioning?

[bd]

Check for power on the brown wire that connects to the A/C selector switch.

[miket007]

Hi BD....

Thanks.

So checking the plug that connects to the AC selector lever on the controller in the cab....with ign on "accessory"....no voltage out of any of the terminals.

I also checked the underhood relay and it seems I have power there but nothing coming out ever.

[bd]

Ignore the blower relay for the time being.  A/C does not power up on "accessory."  Recheck for power on the brown wire that connects to the A/C selector switch with the ignition switch in the "run" position.

[miket007]

Nothing out of that plug with the engine running.

I am not sure if it makes a difference but I have the entire HVAC controller out of the dash...the blower speed switch is disconnected when performing the above test.

[bd]

With the ignition switch in the "run" position, probe both sides of the HEATER-A/C fuse using an incandescent test light (do not use an LED test light and do not use a voltmeter).  Probe both end caps of the fuse and both fuse sockets (terminal clips).

[miket007]

Thanks I will give that a shot later today

[miket007]

out of all the things....it was a bad fuse. It wasn't showing blown....but it was bad.

Thanks.

[VileZambonie]

A "bad fuse" is a fuse that failed to protect a circuit and allowed your truck to go up in flames. So it was a "good fuse" that did its job.

If it blows again, don't keep throwing fuses in

[miket007]

Yes! Wrong terminology...it didn't blow like a normal fuse does, but wouldn't pass current. Replaced it and all seems fine. I must be getting lazy in my years....I should have checked it first with a tester. It passed the visual.