[70GMCer]

You need a volt meter to see if you are getting 12 volts to the motor when it is heater control switch is on. Test it at the firewall where you unplug the wire that is on the motor. Turn the fan switch on and then take 1 meter test lead to that wire and the other lead to a negative ground. If the meter shows 12 volt, it is good. Do this to all the speeds on the heater control. If no voltage, work your way back to the heater control testing for voltages.