2003 Hummer H2 - Air will not come out of vents and circulation does not work. Heating, cooling, and blower works fine however

Question

Air will not come out of vents for either head or legs. The blower works just fine and I feel air coming into the cabin at different crevices of the dashboard but I don't feel anything when I put my hand or arm over the vents. Heating and cooling works fine as well.
I checked the HVAC fuse and it's good. Other than that, I don't know what could be causing the problem. Another fuse for it that's bad, a bad relay, or a loose connection? Thank you for everyone's help.
Edit: Another thing I should add is that the circulator fails to come on when I try to turn it on. Defrost will work however. Air will come out of the vent for defrosting the windshield, but not the vents for head or legs when I set it to that.

Jupiter · Answer

You have a mode door problem. Either your mode door is sticking, or the mode door actuator (moter) is faulty, or the wiring to the actuator is faulty, or the head unit is faulty. If the mode door sticks, it will sense the sticking and revert to the default mode to defrost if possible. If the actuator is faulty, it will also go to the default position if possible. Same with a bad head unit. This needs to be diagnosed to find out which of these problems are present. Most automatic climate control systems have a manual calibration option to calibrate the actuators. This is the first step I take in these instances, but rarely effective because they do on occasion self calibrate. The procedure for manual calibration for your car can probably be found with Google.

Answered by Jupiter on June 19, 2021

2003 Hummer H2 - Air will not come out of vents and circulation does not work. Heating, cooling, and blower works fine however

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