Ok my 2000 bonneville has dual heat and it is not putting out the heat it used to. When we just had a cold snap it was real bad. The engine temp is ok and when I switch to defrost the air comes out hot and strong but when I put it on the floor its barely warm same if I put it on the front vents. If it were the blend doors why do I have good heat out of the defrost? Can I take the the blend door actuator off and test it? If it was a plugged core wouldn't the temp be the same from defrost to floor? Any help would be great Thanks.

You can watch the blend door and other actuators work in place. The rotating part is white, so while manipulating the dash control you can see the associated actuator move.


Did you have the temp demand setting on 90?
Was the engine fully warmed up?
What was the outside temperature sensor reading? Was it correct for the ambient?

My thinking is like yours. Since the unit puts out hot air for the defrost, it should put out hot air for the floor vents. Set on 90 deg, that should force the blend door(*) to full hot, and I think that also applies to 85 deg.

The difference is that the sensor in the dash and the passenger sensor get feedback from the temp of the air through the air channel. So it modulates the blend doors to anticipate the right change in cabin temp to match the demand from the control panels. Air coming out the floor that is hot might be sensed more by the cabin air tube that comes to the holes in the dash. But set on 90, that modulation should be bypassed.

If the actuators move full hot for defrost, the actuator and blend door attached to it must be okay.

Thanks. I had the drivers side cover off under the dash for some work on something about year ago and never got around to putting that cover back on witch has that air sensor in it. I never gave it thought that might affect the heating system. Does those sensors ever go bad?? I'm going to put it back on and see what happens.