Blower motor woes

[motorcritter]

['71 C10 LB, 402, TH400, bunch of Cheyenne options- w/ factory A/C.

The blower only worked on high speed, and I didn't care, as it was warm out (A/C inop- locked-up compressor). Then it got colder, and it was OK, until the blower quit blowing on any speed. So, the fuse is good, it's got power. The motor is good, and the GM guys must have studied at Benz or BMW, so they could make a nice, challenging HVAC system to work on. Anyway, the blower relay had some corrosion inside it (of course I opened it!), but it cleaned up easily, and worked when powered up. I put an extra ground lead on the motor, also. The switch cleaned up easily, also, and worked properly- juice going where it was directed to. The wiring also had continuity (thanks to whoever put up the wiring diagram elsewhere on the board). I pulled the center section out, to access the resistor (gotta be it, right), and it had a small scorched part where one coil touched the bracket at some point. I cleaned it up and rearranged the coils, and they both had continuity and different resistance values. But- the big ol' but, when everything is snapped together- I still have only high speed! At one point, when going through the components I had all three speeds. When I thought- 'Ah-ha, button it up!', I was back to single speed.

Do I need an exorcist, or did Delco-Remy have Joe Lucas or Robert Bosch building this truck?
Any suggestions would be appreciated. And, yes, I cleaned all the connectors and replaced stff that was nappy. I even used my genuine Honda dielectric grease on the switch when I went through it.

[Tom Vogel]

Trust me.. its the switch.

[motorcritter]

I bypassed the switch, jumping the hot lead to the blower leads. The lower speeds worked for a few seconds- well, the middle one did, and then quit. The low speed never got a chance to disappoint me. I heard the relay click on high speed, like it is supposed to. I got continutiy through all stages of the switch. I would really hate to have to dig back in, but I really don't want to throw all new stuff at it. Any ideas would be welcomed. Thanks, TomVogel, it was a good suggestion, but I'm not convinced, at least, not yet.
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[68K30]

resistor

[motorcritter]

Deep in the guts of the cavernous heater box, awaits the malevolent blower motor resistor.

Thanks for the advice. Not that I want to go back in there so soon.
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[Katrina/10]

Did you replace the blower motor?

[motorcritter]

Motor runs great- it just doesn't run on low or medium speeds. It has, on a rare occasion, and only for a few moments, run in low or medium speeds. The resistor had a burnt sopot on one coil where it touched the bracket. It had resistance and continuity through both coils, so I am not so quick to condemn the resistor. I get continuity with normal resistance through all switch positions, and the blower relay engages when powered up. I got continuity on all wires, and added grounds to the motor and relay.

Still pondering tearing open again, I just wish I had a firm idea of what is amiss. Plus, the '79 K20 motor replacement is now becoming a time-critical project. Only so many hours in a day.
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[Katrina/10]

I had a similar problem, everything tested fine, but the fan would not run on low speed. So in desperation, I replaced the motor even though it seemed to work. Suddenly I had all fan speeds! I got a NAPA motor for about 20 bucks.