Depending on the year. My 98 Exp EB has the knob on the dash to change the temp in the front and the console on the roof has another knob to change temps in the back
End panel vents
If you are attempting to remove the center air vents in the dash panel you will need to: 1. Remove the driver side Cigarette Lighter and the Passenger side Auxiliary plug-in. To do this locate the slot at the bottom on the each of these that will allow you to pop it loose with a screw driver. 2. After removing the panels un plug them and set them aside. You will then see 2 screws, remove these. 3. Carefully pry the panel loose. It will pop off but use gentle force so you do not break the panel. The air vents come off with the panel. From there you can remove them or clean them...
check fuses
actuator under center of dash is bad
How easy is it to replace head gasket on 1994 firebird lt1 motor
heater core, tough job.take it to a qualified auto technician
most vehicles use a vacuum diaphragm to move the mode door inside the dash from the floor to the vents to the windshield. Either the vacuum diaphragm is leaking or the vacuum hose has become disconnected. In my 85 topaz the door pannel vents are used to defrost the side windows.
To allow for cooling, so the head does not get too hot.
I believe the upper vents are for A/C only. The floor vents are for the Hot air. Test your ceiling controls by moving the knob from cold to hot, you should hear the air pass from upper vents to lower vents. Providing of course you have selected REAR from the front control panel.
The vents allow the loft space to breath. By blocking it can cause damp air to accumilate and thereafter you have condensation damp and mould.
IF a Vaccume hose comes off OR is bad going 2 the DASH Controls that will happen OR a bad Actuator or Actuator door (stuck) will cause that.Make sure the vaccume Canister is not cracked (if it hs one) Usally it's a very small Vaccume line(hose) that causes the Problem. You either have a vacuum leak in the heater control system, or a cable that has come off of its control panel...
Check for a broken vacuum line by the battery. These lines get brittle and break with age.