That click-click-click behind the dash on GMT800 and GMT900 trucks is a blend door actuator chewing on its own stripped gears. Easy part, cheap part — but these trucks have three or four of them (driver temp, passenger temp, mode, recirc), and half the “I replaced it and it’s still broken” stories are either the wrong actuator or a skipped relearn.
The relearn that actually works: ignition off, HVAC/BATT fuse out for 10+ seconds, fuse back in, start the truck, then hands off the climate controls for about 40 seconds while it self-calibrates.
Full write-up (which actuator by symptom, replacement, relearn): Chevy Blend Door Actuator: Clicking Dash Diagnosis, Fix and Relearn
Your turn:
- Which actuator was it on yours, and what was the symptom — one side hot, stuck on defrost, or just the clicking?
- How bad was access on your cab? Anyone conquered the glovebox-side one on a Tahoe?
- Did you know about the fuse-pull relearn the first time, or learn it the hard way?
- Post your stripped-gear photos if you cracked the old one open.