Verified answer

You didn't say if it is an LS, LT, SS so will need to know what engine option it has, the 3.4L V-6 or the 3.8L V-6?

The fan runs but no air comes out of the vents?...could be a bad or broken "blend door" which directs the flow of air through the heater core/vents or the actuator for it is bad, a blown fuse or a bad temp control switch or wiring issue. The blend door inside the HVAC ducting controls the flow of air through the heater core and a/c evaporator based on the temp setting and heater control switch for recirculate / inside or outside air....another door called the mode door directs airflow to the top, middle or lower heater vents which is controlled by the mode switch.

A shop would have to diagnose the problem further. You can also try to recalibrate the actuator for the blend door to see if that solves it.

"Actuator Recalibration

Calibration Procedure

Use the following steps to perform the calibration update:

Turn OFF the ignition.

Remove the battery positive voltage circuit fuse of the HVAC Control Module.Important: The module memory will not clear if the battery positive voltage circuit fuse is installed in less than 60 seconds.

Wait 60 seconds.

Install the fuse.

Wait 60 seconds before moving the HVAC controls."

http://chevroletforum.com/forum/monte-carlo-lumina...

check your radiator level