Loud Clicking Noise When Rear A/C is on

[mflusche]

I Have a 2002 Trailblazer and when i turn on the rear A/C there is a loud clicking sound coming from the back of the truck. It is on the passenger side up by the interior light in the third row. If i turn off the Rear A/C or turn the knob and have both the overhead and the feet blow out it does not click.

[Ol'Jim]

Anyone have any idea what causes (or solves) this problem? My GF is having the same issue with her 2004 TB EXT. When she first starts up, it makes a loud noise in upper, pass side, rear of cabin. Like up in roof liner, or rear A/C ductwork. It is a rhythmic, whap-whap-whapping sound, about 1x per second. About a block later, it either quits, or doubles in speed, to twice per second, then eventually stops. Next trip, same thing.
Tried messing with the different HVAC controls for front & rear, doesn't seem to affect it.
Have searched the boards, this was the only thread I could find that sounded like same problem.

[maxwedge]

Jim, sounds like a mode door actuator similar to what can occur in the front temp door actuators.

[DeltaP]

Agree, rear a/c mode door actuator keeps running and can't find a "park" position so the door keeps flapping. Pretty common on gm's and fords. Replace the actuator and all should be good.