My 1997 Chevy, Lumina, 3.1 L
Ok, I have this weird problem with my vent system. You know how there are 3
different vents positions (floor, the ones on the instrument panel, and the one under
the windshield) but lately I can't switch to the ones on the instrument panel and the
other two don't come off. Also my A/C is very
weak and I think it doesn't work properly. (I am sure that the switches
them self work just fine, I think it's some thing else)


BL:
Sounds like definitely a vacuum problem. The mode switch on the control head
controls the vacuum/electric solenoid block, which in turn, directs vacuum to the
proper mode or blend doors. When there is a loss of main vacuum to the solenoid,
the system defaults to def/flor for safety reasons. First need to check for vacuum at
the purple and the black hoses on the solenoid assembly with the engine running.
That is under pass. side dash, above the blower motor. If no vacuum, check vacuum
into the vacuum ball. The engine supplies vacuum to it. The vacuum ball is under
the dr. side inner wheel well shield. One hose should have vacuum in, the other
goes to the solenoid assembly. If vacuum at the solenoid, possible control head
switch problem.

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