2005 Av - Problems w/ HVAC ? Mode not working (floor, defrost, dash, mixed, etc)

2005 Avalanche with manual HVAC.  Was only blowing out the defrost vents regardless of mode switch position.  I checked the mode actuator (upper right area of accelerator pedal) and it was not moving, or in some cases seemed like it tried to move but only 1/8? or so and then moved back to where it started.  I replaced the mode actuator and now when I turn on the ignition, the actuator cycles all the way one way then all the way back where it started.  Then it does not move when I move the mode switch on the dash control knob.

I did the calibration procedure from the manual where I pulled the HVAC/ECAS fuse, waited 10 sec, replaced the fused, started the truck, waited 40 seconds and still nothing other than the usual 1 cycle back and forth as I stated earlier.

I tested the wiring to the mode actuator.  Getting 12 volts on the Brown wire, 2.5 volts on the tan wire, 5 volts on the Light blue wire, 0 volts on the yellow wire, and 0 volts on the light green wire (maybe some mV but not sure).  I tested continuity from the mode actuator connector to the HVAC controller connector and have continuity on the yellow and light green wires.

This leads me to suspect the HVAC control unit in the dash, but I am not sure how to test it any more. It seems unlikley that the dash unit would go bad but I?ve seen stranger things.

Any thoughts?

can you scan it for codes? specifically for body codes.


step one in the recalibration procedure is to clear codes.

ItsStopher said:

can you scan it for codes? specifically for body codes.


step one in the recalibration procedure is to clear codes.

Click to expand...

I do not have any code reader.  After researching it looks like most do not allow viewing of the body codes for HVAC.  In the factory service manual, it is strange as they have a specific section that says how to do it without a scan tool and the first step is  "Clear all DTCs"! 

Well, upon further review I have found a Bluetooth/iPhone type OBDii unit that can do the body codes for my truck.    Actually looks like a really nice unit called "Bluedriver"  for $99.95 on Amazon and Prime 1 day!  Seems like a much better way to go than a handheld in today's world.  Great reviews.  We will see what it says.....

To close the loop.  I had a bad mode actuator that was replaced but still the system not working.  Had to also replace the HVAC control module unit in the dash and then it worked but was not getting to full face, meaning the actuator stopped short (even after calibration).  I had to open the mode actuator and carefully jump the output gear 2 teeth and now it works perfectly (I read this is not uncommon).  The actuator I bought was a $20 no name brand.  Next time I'll at least buy the Dorman version or better yet the AC Delco.

The BlueDriver Bluetooth scan tool I bought is fantastic and reads all of the codes including B Body codes.  I got codes B0263 (Air Flow Control 6 Circuit feedback circuit malfunction) and B3770 (Air Flow Control 6 Feedback Circuit).    The app on my phone also allows you to look at common solutions and in my casew the #1 was to replace the mode actuator and #2 was to replace the HVAC control module.

Thanks for the help.