Hello all- new to the board Just purchased a 01 HD that needs some TLC. One of the problems I'm working is the AC/Heating system. Only distributes air through the defrost vents, no matter the position. Also, no blower motor speed change with corrosponding switch positioned. Jumpered the blower relay, blower motor works in all positions. Fuses at both the interior and engine bay panels have been checked and replaced with fresh fuses. Swapped the blower relay with a known-good relay, no change. AC works just fine, about 48*.

Outside of a obvious break in the wire from F24 to the relay, or a bad ground, what other cause can it be?

Without swapping the blend door actuator and checking the ground, any other possible issues? And where is the actuator located? Bad vaccum signal to the panel?

 

Outlet control is via vacuum. Check the vacuum line that runs behind the battery then through the firewall.

Is the blower on HIGH all the time? If so, check the blower resistor pack.

Steve