2003 GMC Envoy Q&A
2003 GMC Envoy Question: Loud knocking in dash when vehicle is started and no air from front vents.
When you start the vehicle there is a loud knocking that goes on for about 1 minute. There is no air coming from the front vents. What is the thing that shifts the vented air around? I wonder if it has somehow become jammed? Air works from floor and windshield vents. - tmlamon
your blend door sctuator has gone bad, that regulates air flow from heater to defrost and a/c. approx cost is 400.00 to replace it.unless its the one that is in the middl of the dash and that one is approx 800.00 - globalhelper
Loss of use in the HVAC directional vents will usually mean a bad mode actuator that needs replaced. - csubak30
the blend door broke off...and is flapping inside the car. - your.mechanic