GMC Repair: 1994 gmc 1500 pickup (350 CID), small screws, gmc 1500

Question
when I first start my 1994 GMC and when I cut it off, there is a loud, fast knocking for 25 seconds and it sounds like the knock is in the dash on the passenger side. What could be causing the knock and how can I fix it. I was told that this knocking was common in the 1993 and 1994 truck models. the truck has 164,000 miles on it.

Answer
Hi
It is the HVAC recirculation door actuator.
It is a common item to make noise. It is located on the HVC air inlet on the passenger side above the glove box.
It is held in with 3 small screws. It is not the easiest item to gain access to.
Basicslly you'll remove the screws, the actuator and reinstall.
I hope this helps.
Good Luck
Pawl