troubleshooting no AC blower fan

[chipmaker]

I have no power to HVAC control unit. Where does the 12v come from on the attached diagram? Fuseblock? I replaced AC fuse already. The fuseblock pic is not mine, just a clear representation. Help!

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[Curt]

It should be relatively easy to narrow down your problem.The fan motor has 2 wires coming off the fuse block to it.Check your voltage at the fan with the switch on,see if you’ve got power.If so,the motor is bad,if not,check and see if you have power to the switch....

 

[chipmaker]

the heater fuse was blown. Now the fuse blows only when fan is set on high. Hmmm. Relay and resister has been replaced.

 

[chipmaker]

replaced fuse, unplugged blower, fuse blew when set to high. 12v goes directly to relay when set to high, it bypasses resister. Relay was already replaced.

 

[chipmaker]

Just wanted to follow up, maybe to help some down the road. I found some info about the relay and doing a strange mod. It did work, this is a repair I would have never thought of. I had narrowed it down for sure to the relay. bought 3 different brands, still blowing heater/blower fuse, but only on high speed. The fix is to remove the silver case of the relay. At one end you will see a small component, it may look like a resistor, but it is a diode. But that isnt important. Whats important is that you cut the leads on both sides and toss it. Make the 2 remaining leads touch nothing.
Removing the diode fixed my issue. Good luck.

http://forum.73-87chevytrucks.com/smforum/index.php?action=dlattach;topic=24383.0;attach=43748;image