2008 Chevy Trailblazer

ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#15714 In Progress 2008 Chevrolet Trailblazer public

Hello Sparky,
Truck is a 2008 Chevy Trailblazer. Truck sat for 6 months, battery was completely dead. I put a new battery in it and now the A/C comes out of every single vent except the vents that aim at your face. Also note that air comes out of the defroster non stop now also. I tried re-calibrating system with many different methods and none have worked. If it is an actuator that is broken, which actuator do I replace? Is there an actuator specifically for the defrost and dash vents? Thank you in advance.


Whenever battery power is lost and reconnected a recalibration begins when the ignition is first turned on. If the controls are adjusted or if an actuator fails to recalibrate the system will be “stuck”. Typically in this body style the mode actuator has been failing for weeks or months leading up to a recalibration event that it cannot pass and your symptom appears.

The following article shows where the actuator is and how to change it. If you have adjustable pedals the gas pedal may need to be removed as part of the replacement procedure.

2003 GMC Envoy, No A/C Vent Control, B0263

Thanks for the reply. Not sure if this helps diagnose it, but when I remove fuse 36 (HVAC B) I get full air coming out of dash. Only thing is , I lose the actual cooling feature. As soon as I plug fuse back in, the vents close again.
Can’t figure out why that’s happening, but I have ordered a new mode actuator and plan on installing it when it arrives. I’m just wondering if I will have the same issue. ?
Thanks again.


I have never tried that so I have no idea if it has any bearing on the diagnosis or not. What I do know is that 95% of the time replacing the mode actuator resolves the issue. As a side note if you can disconnect the mode actuator harness while the air is blowing out of the desired dash vent position, then reinstall the fuse you should wind up with a more tolerable a/c.

Ok awesome I will try that . Thanks I’ll be in touch

Don’t know if my last reply showed up, but thanks again!. I installed the new mode actuator and it works great. I took apart the old one and the main internal gear connected to the main shaft was cracked allowing it to just spin freely.


Glad to hear everything went well. Thanks for the donations too.

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