2011 GMC Acadia AC or heat not blowing through vents?

That's a common problem and usually due to a faulty mode door actuator which controls air flow to the various dash vents based on heater control settings. If the actuator fails, the default position of the mode door is to blow air from the bottom or top vents. In some cases, you might be able to pull the HVAC system fuse for a minute, then replace the fuse and turn ignition key on without starting the engine...the system will go through a reset/check mode which may return the function to the actuator.

If that does not help, you'll likely have to test or replace the actuator...located behind and left of the glove box. Some models may also have a warped area around the mode door which requires more work to remove/replace. Links below have details....similar model to a Traverse. The HVAC system has a few other actuators so make sure to get the right one....should be a part number tag on the old one.

http://www.acadiaforum.net/index.php?PHPSESSID=2df...

https://www.youtube.com/watch?v=YJbx3b6SPow

http://www.justanswer.com/gmc/8zy15-gmc-acadia-sle...

http://www.oreillyauto.com/site/c/search/Blend+Doo...

If it blows on all settings (hi-low) then don't worry about your blower. I would put my money on the blend door actuator, listen closely and switch from one vent source to the next if you can hear a little motor whirring you might be looking at the blend door assembly instead but as JJ says they will be very difficult to change on most cars and i would recommend bringing it to a shop to be properly diagnosed/changed due to difficulty.

Let me know what happens

On the extraodinarily difficult to reach door actuators may have failed in the duct housing.

The blower motor isn't working.

It could be many things. Check the fuse to your blower motor.