Heater problems

[woody367]

I have a 99 Yukon. The heater just started to give me problems, it blows out the defrost and the floor when it is set for just the floor. It works fine in every other setting even just defrost. Any ideas? I do not like the heat in my face while driving.

 

[SunlitComet]

Look under the dash above the gas pedal. There is a drive motor there with two linkages on it for doors inside the box. Make sure both are connected and move as you select different modes.