Heater Controls

For the last couple of years, I’ve noticed the air flow changes from the floor to the defroster under hard acceleration. Not a big deal. This morning (7 degrees) the airflow was changing under light to moderate acceleration.

It’s a vacuum problem, but is there anything in particular I should be looking at? The car is running fine, no issues with stalling or hesitation.

Thanks in advance,

Ed B.

There should be a vacuum reservoir tank under the hood somewhere. Its job is to supply vacuum to the vent doors while the engine is under acceleration and has a low vacuum level. There may be a crack to the tank or restrictor problem.

The control itself could be leaking. This happened in my Ranger. In my Olds Silhouette, it was a mechanical control, and the silicone manifold was leaking. It’s a minor leak, since it is only under hard accel (the cold shrinks components, so the leak could be worse)

Most likely a bad check valve. The check valve is supposed to maintain vacuum in the climate control lines when the engine vacuum drops. Just another thing to look for.

Thanks for the suggestions, I will have to crack open the Factory Service manual and see what’s where.

Ed B.