roundball

Replaced the battery in my 2007 Trailblazer a couple weeks ago...in cool weather I've had the heater on the floor.
But today, it was unseasonably warm and I'd set to blow outside air through the dash vents but nothing comes out.
All other controls are working, fan is blowing all speeds, air blows up out through defrost and down onto the floor, just not out through the in-dash vents.

I've been searching the web and have seen a few references to this being a known problem...pull an HVAC-B fuse and wait then reinstall, and start the vehicle to let the mode actuators recalibrate or something.

Then found this great looking site and hoped to get some assistance...if anyone has any more specific info or confirmation of this problem and fix I'd appreciate the clarification, thanks.

Chevrolet Customer Service

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The HVAC actuator is a possible culprit. This is just a suggestion, not a diagnosis. I encourage you to have the vehicle inspected by a certified technician. They will be able to offer additional information after a physical inspection.

Please keep us posted.

Louis
GM Customer Service

roundball

I'm certainly aware that 'certified technicians' are available, of course.

Having preferred to do as much of my own maintenance as possible throughout my lifetime I'm in the information gathering stage right now.
All indications so far suggest this is a quality design / parts defect problem already known by GM...was just looking for 2-3 different sources to corroborate the initial findings before I go forward.

By its title, this Forum is not an official "GM / Chevrolet" site...so I'm a little surprised at your reply...particularly including your title, officially representing GM Customer Service.

Can you elaborate on that?

Chevrolet Customer Service

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You are correct; this is not an official GM forum. The GM Customer Service teams are members on several forums. We try to offer customer service in various mediums, including social media. Although I am not a technician, I can offer customer service in many different situations.

If you have any questions in the future, please feel free to contact me.

Louis
GM Customer Service

cleveland63b

Sounds like you've already looked into the most common options, either the HVAC system needs recalibrated or the mode actuator isnt working

roundball

Thanks, that's been my initial search findings so far.
That the actuator(s) lost calibration when the battery was disconnected for replacement...and that the associated GM parts quality problem is certain of the actuators can't or won't recalibrate, resulting in the cost of replacing one or both of them.

farago2r

I had a similar issue. Air would only blow out of defrost vents. But this worked for me:

1) Unplug HVAC fuse for 10-30 seconds
2) Start truck
3) A/C comes out defrost - wait about 10 to 15 secs
4) A/C then starts coming out the floor vents for about 5 seconds
5) A/C then starts coming out the dash vents.
6) While the A/C is coming out the dash vents, turn A/C OFF (otherwise it cycles back to defrost for good).
7) Turn truck OFF
8) Restart truck and it should work fine

(Found solution on another forum from user "ccurran")

roundball

Thanks for posting this...yours is the most specific, detailed possibility I've seen so far regarding the HVAC fuse approach.

May not work for my situation, but nothing ventured / nothing gained...and I'm off today so I'll print this and go give it a try later this morning.

roundball

Unfortunately, it didn't help my situation...thanks for trying

roundball

Tight schedules, and temps starting to get to the point where air conditioning would be nice, against my better judgement I took the Trailblazer to the GM dealer.
They said the gears were stripped inside the little actuator unit...an hours work, $380 to drive away...once again proving that car dealerships are total rip offs.

Trying to decide who I'm more disgusted with...them...or me because I knew better and let them do it anyway.

My Wife has an identical 2007 Trailblazer...even the same color...bought them both at the same time...so I told the guy it was time for me to put a new battery in her car as well and I didn't want to go through this crap again.
He says, after changing a battery, leave all A/C controls off...start the vehicle and let it run a few minutes for everything to recalibrate.

Told him I had bought the set of GM Shop Manuals for the T/Bs like I have for other Chevy's all my life and there was no mention of that in the manuals at all...he just shrugged and said they don't put each and every detail in them...they're running a service business.


GM must really be proud...will be looking at other brands next time for sure