So I recently picked up this 03 z71 because the previous owner thought it needed a motor (it was smoking) 30$ set of valve cover gaskets and its back. But, that being said it still has a weird hvac problem. If you unplug the battery and then hook it back up the blower motor works for about 2 days then stops and wont run on any speed. The resistor looks likes it been changed recently and I had a spare blower motor and confirmed thats not the issue. What could it be? Dash hvac not rear. Thank you.

 

When it's not working give the motor a smack and see if it starts up is the quick check. Brushes in the motor wear down and make a poor contact. Spare motor could be worn also.
Next is checking for power to the motor itself when it acts up. Look at the resistor connector for signs of overheating due to a bad connection.

 

the resistor and the connector to it have both been replaced the motor connector seems to always get 12v? Hitting the motors does nothing there is an occasional electrical fire smell in the vehicle. Maybe a bad ground on the resistor harness?

 

Better start inspecting the harness and modules for signs of overheating. Electrical smell means something is burning up and hopefully doesn't really catch fire and total the truck. Having the wiring diagram for the truck to see what is what is now coming into play.