HVAC Malfunction

Driving home tonight with the heater on. The air was in the defrost/foot position. I switched to head/foot position and when I did so I heard two popping sounds from behind the gauge panel. Now the air comes out from all three positions head foot and defrost. So did one of the panels break or what? And does anybody have a diagram of the HVAC system? Also I'm guessing it'd be a ***** to fix because I'd have to pull apart everything.

Bye bye blend door

I think that's actually the mode door, if I understand correctly the blend door regulates how much cold/hot air comes out and mode door determines which vents it comes out of

Armyman14 said:

I think that's actually the mode door, if I understand correctly the blend door regulates how much cold/hot air comes out and mode door determines which vents it comes out of

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^^^ This. Heatertreater has the fix and shows how to do it. But it is not cheap. Although it is a "permanent" fix.

This is pretty old haha.

This actually fixed itself once the truck turned off. I don't know what happened, but it works fine now.

Is this crap random or does it usually start failing at certain mileage?

hotkarl said:

Is this crap random or does it usually start failing at certain mileage?

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The way the doors are setup causes the failure randomly. What happens is the pcm cycles the door's motors randomly to check the limiters. Now that would not be so bad IF the parts were not all PLASTIC. When the motor gets into a bind at the stops for the door it will continue to try and move the door further, most times it stops after a second or so. But sometimes it will not and next thing you know the piece that goes into the motor breaks off, rendering the door inoperable until it is fixed. A bad design to say the least. What heater treater has done is make the door and its connections out of metal which will not break. The motor will fail before the door breaks.

Here is a link to Heater Treater: HeaterTreater™

The fix is a bit expensive, but will last a very long time, if it ever breaks.

I had an Explorer that had a similar and inherent issue with the blend door. Same crap where the plastic part on the door would break where it connects to the actuator. The proper fix is to drop the dash which we all know is a suck job. The quick fix which I did was to drop down the glove box and cut an access hole in the box and rig up a manual cable to the door. Worked great. There is a time and place for plastic but sometimes I gotta wonder what these "engineers" were thinking with some of these designs. The hvac stuff, timing chain guides, etc...it's like "really?".