I have a 2000 Chevy blazer 4wd. The blower motor won't work on high. I have changed the relay, changed the resistor and ran 12 volts to the fan directly and that will make it run on high. I have also replaced the fan switch! I am pulling my hair out. For some reason I can't get 12 volts to the motor! Please help!!!

 

The power for the blower motor goes through the resistor network for the lower speeds but for the highest blower speed the relay removes the resistor network and a full 12v is routed to the blower motor. This routing is of course managed by the HVAC controller in the dash. Do you have and know how to use a digital multimeter? It also uses a dufferent power feed and fuse. Check the 30A HVAC fuse in the UHFB.

George

 

I have checked the fuse and it is good. Which wire on the blower motor relay sends the full 12 volts to the motor? There are 2 orange wires. One is a smaller wire. I am using a multimeter.

 

When using the three lower fan speeds the HVAC controller in the dash provides the power then through the selected resistor value then to the HVAC relay where all of that is just passed through the idle relay onto the purple blower motor wire. When you turn the HVAC controller to high what happens is the HVAC controller power and the resistor network are taken out of the circuit because the coil in the relay is energized by the orange wire from the controller to pin86 on the relay which then connects 12v from the 30a HVAC fuse on the bigger orange wire through the relay contacts onto the same purple motor wire. You need to determine if the hvac controller is supplying the energizing voltage to the relay coil on high speed and if so is the coil ground good and if so is the relay switching and if so is the large orange wire supplying 12v under the full motor load. Let me know if you need help with any of this. It’s always better to test for the proper voltages under the full circuit load.


George

 

Here’s the circuit:





George