2009 Tahoe.
For the longest time when putting the blower on max, (what I think is the) blend door would move between face and feet. and back/forth back / forth. so I never really used max. outside of that it seemed to work ok, even if it was slow to react to changes from face / feet when set with the controls.

Now, it seems to have a mind of it's own. even with the system 'off' i get hot or cold through the vents. this morning it couldn't decide if it should be hot or cold, and even when set to feet manually, it still comes out the dash!

am I correct to replace the blend door actuator as a troubleshooting step and or fix?

Does the blend door just do temp or does it do dash/floor, or are there 2 units/motors?

thanks

 

Welp, I found the 'mode door' actuator, it's behind the driver knee bolster. there has been an intermittent clicking noise from this area for YEARS.

Doesn't look too hard to replace, so I'm going to start here, since the mode seems to be the first issue.
Once replaced, I'll see if it works and what happens with the temps.

is the 'mode' actuator and 'blend' actuator the same part? There seems to be 3 in the vehicle total, but I think they used the same actuator for all 3.

1 mode: dash vs. feet output
1 temp - driver
1 temp - passenger

 

Strike that.
I think this is the mode actuator:
https://shop.advanceautoparts.com/p/...+door+actuator

and this is the temp one:
https://shop.advanceautoparts.com/p/...+door+actuator

 

In any case, I'll take it apart first and hope it has a part number right on the thing.

 

when you remove the actuator...check the splines on the door....something may be stripped or cracked. move the blend door with your fingers...it should move smoothly and fairly easy through it complete range. if you have a good scan tool...you can watch the "door counter" number accumulate and and count down as it moves through it range of motion.

 

Good idea. No scan tool...



The mode door seems to move smoothly no issue. I removed the driver knee panel and the offending actuator. The click click noise at start is now GONE. been dealing with that for years. I ordered the part online, so I didn't get to replace it yet.

I think I'm on the right path as the clicking seems to be gone.

I took the time to notice that the driver vents were blowing much colder than the passenger. and the car can't seem too keep a temp. Perhaps in addition to the mode door issue, there is as blend door issue w/the driver side. ugh. I will fix the mode door first and see what happens.

 

To calibrate I see to remove the HVAC/ECAS fuse. but I don't see that labeled.

I see at least 2 fuses related to HVAC

39 Climate Controls (Battery)
55 Climate Controls (Ignition) (Prolly not it)

ECAS does not appear in the owner's manual (anywhere)

I guess I could just unplug the battery for 30 seconds... that's really the same thing...?

 

disconnecting the battery will not initiate a hvac door calibration.... the manual calibration involves pressing the ac and recirc buttons 3 times....something like that...when in calibration mode the ac and recir leds will flash.

 

...That's not what the factory service manual says..? Just says to:
Key off
Pull fuse 10 sec +
Replace fuse
Key on, don't touch A/C for 40 sec +

This is from the GM manual, so I'm not sure if you have other info are or thinking of another vehicle?

 

FIXED!
The new mode door actuator works! I did the above and watched as it moved both ways a few times on start.

Now the HVAC in the car is much more consistent. Wish I did this years ago...