Cabin air sensor aspirator location?

[Robert Picard]

In trying to get some heat, I have changed pretty much everything in my 05 Sierra's HVAC system except for the cabin air sensor aspirator. I tried to search YouTube for location of that unit and all I can find is the one with the little speaker type grille in the headliner over the driver's head. I have a single cab and nowhere on the entire headliner can I see anything that looks like what's on YouTube.  Where is it located so I can replace it wit a new one?

[PopeyeD]

Over the driver's head behind the headliner in my truck.  Looks like a miniature waffle about 1.5" across.  Might be making a whirring sound with the system on.  It is not a fan for the driver's head as some boneheads might think.  Maybe your truck doesn't have it in it's system?