Return air vents.........
computer says no
You can use a scuba tank, but that is it.
yes
I'm not sure what vents you are talking about, but usually air vents are known to be working if there is air flowing through them.
the middle vents only supply air from the ac unit using a separate in dash fan. the floor and defrost vents come only from the heater
Cold air return vents are the ones on the wall
If the air vents of the Chevy trailblazer 2004 are not blowing air, have the fuel pump checked.
You have to remove the vents of the air ducts. Then use a vacuum to remove any debris. After that you can use a stringy mop to dust the rest of the vent out.
The air is off.
You have a primary and secondary tank. Certain air functions of the truck use the primary and others use the secondary tank.
The heater may not be on - but the fan still blows air through the vents when they're open !