Heater Air Flap

I think the flap that mixes hot and cold air is broken. I can move the control from cold to hot, and the cable moves the arm that sticks out of the flap, but all I get is cold air. Has anyone else encountered this? I do have vacuum to the controls on the drivers side under the dash.

First you should be aware that the heater valve itself is vacuum controlled, so before blaming the flaps make sure that the valve is actually working and the heater core getting hot. That valve is in the engine compartment, on the heater hoses, so easy to spot.

Also rmember that when you push the position control all the way to the left, to "off" it opens a fresh-air flap that bypasses the entire heater. Make sure that that flap is not stuck open, damaged, etc. It's down low on the right.