GMC Repair: Blower problems - 93 GMC Sierra, gmc sierra, heater blower

Question
Just got a '93 GMC Sierra 1500. The heater blower sounds like it is working fine, but on high, there is not much airflow out of any of the vents.This is true for A/C or heat, floor or dashboard vents. On defrost, there is next to no airflow out of the windshield defrosting vents, although the vents on the sides of the dashboard that blow on the side windows have strong airflow. When the switch is pushed to go to defrost, it sounds like you can hear a door/flap being moved, but it seems like all the airflow is coming out those 2 side vents.  Thanks for your answer, and for all the help you have been to other questioners.

Answer
Gm has had this problem for years. If you look up under the dash you will see either some electric or vacuum operates motors. Watch these motors are you select different settings and the one that moves the LEAST will be your problem controller. Replacement and or adjustment is required.


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