88 silverado defroster

I just notice me heater will not direct the air through the defrost vents. It has the push button controls (v.s. the sliding controls).
What should I look for?
Does it operate by electric motors, cables, vacuum lines?
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Greetings,
It operates by an electric motor that moves a flap that directs air through whichever vent position you have selected. The master flap is located under the center of the dash in the middle and you can feel it if you reach your fingers up through the floor air vents.
If you are lucky, it is nothing more than the flap edge stuck to the wall of the vent and won't move to open up and send air to the defroster vents. I can remember cleaning mine several times because the rubber edge of the flap gets sticky with age. If you are unlucky it is a burned out servo motor that moves the flap or a stripped gear and will need to be replaced. The motor and gears are located up under the dash on the passengers side of the center air box. You should be able to find a replacement easily enough in a junk yard for only a few bucks as these spanned many model years.
Cheers - Jonathan

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