2004 Olds Alero - My air is blowing on the floor and defrost/windshield. The knob will no longer change the air to blow from any other vents. I can change the temperature and speed. The knob just twists, and can be pulled off. Is it the knob only? or do I need to replace the (three knob) control unit? How do I know? Thank you!
Check in the side of the knob for a small screw
SOURCE: air flow selector
Your mode door is controlled by vacuum check the vacuum hose on the left side of the intake manifold. these some times fall off leaving your mode door with no vacuum and the default position of the mod door is defrost.
SOURCE: 98 Safari vent selection failure
along the fire wall follow the vacuum line. it is very small 3/32? and made of plastic which deteriorates over time. best to buy a rubber piece that fits over the plastic and link the two pieces together
SOURCE: Air duct doors fail to operate when using the selector knob.
There is a very small black hose that provides vacuum to operate the different vacuum motors in the system through the switch you mentioned, that switch simply diverts vacuum to what ever air outlet u select, the vacuum comes from the engine, it goes through the firewall on tha passenger side, like I said it is a small black hose.
SOURCE: 1998 Mustang - AC blows only through Defrost vents
You probably have a vacuum leak on the passenger side. its a small plastic hose some times they come unpluged from the engine. or brake.
SOURCE: HVAC vent selector does not function. Air flow is
THe blend door seems to be stuck. When you change settings from defrost to floor air or, vent, the blend door opens and closes directing the air to the place you want it to go to. I have had some success spraying a lubricating oil such as WD40 under the dash on the blend door. You need to get under the dash with a flashlight to locate it. It looks like a flap. Spray it with a couple of shots of the WD40. Go easy on the spraying as you may be inhaling the fumes. Keep the doors and windows open to minimize the fumes. Wait about 1/2 hour and try the A/C functions. (defrost, floor, vent air)
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