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Does the blend door control which vents are receiving air from the blower?
No. The "blend" door controls how much air passes through or bypasses the heater core. It is for temperature control only and is electrically operated.
The other doors in the plenum control inlet (fresh/recirculate) and outlet (defrost/panel/floor) airflow and are all vacuum-operated.
Well, if you have a vacuum leak the HVAC will default to defrost. Probably not your question though.
Thats why I was asking, it’s been occasionally defaulting to defrost. This panel looks like my 97 f250 panel and I know it’s all vacuum..
Guess I’ll need to find a trouble shoot diagram on the vacuum controls….
