Why will not switch from vents to floor or defrost

the ERG shouldn't have anything to do with what vents the AC comes out of, rather the dash switch that exists for changing from defrost to main vents to floor vents controls what vents are used.

I think the flaps are sticking

does it blow through the defrost vent only when you switch to vent/floor or does it blow through defrost and vent/floor? is it a switch that is just electric or a manual lever that you slide? the manual type will have that problem if the diverter or the linkage behind the lever(in the dash behind the panel......may be able to access underneath) becomes broken or disconnected so that the air is diverted to defrost regardless where you move it.if you can get to it, you will see what is broken or maybe a fastenerr fell off.

probably a vaccum tube disconected.

Sounds like you need a blower door acuator motor, which moves to direct the heat to where you want it to be

it sounds like the switch lever for the vents, floor and defrost is not switching the vent door that goes to the defroster hose. You need to pull the switch consol out loose from the dash and follow the cable for the defrost that goes to the hose for the defrost. You might also have a broke switch that won't pull the cable enough to open the air for the defrost hose.

cannot switch from defrost to panel airflow 2001 chevy silverado

the switch where you turn it to blowing at your head is probably out. you will need to replace the switch control where your defrost, foot, head etc. what make, model, year is your vehicle?

Check for a vacum leak from the engine to the a/c.The color of the hose is black. Also check if the heater control valve hose is unplugged. If you have vacuum the it sounds like the door for the vent/floor/defrost is broken.

Yes it is cable operated and something is probably disconnected. Remove your glove box so you can get a better look at whats going on.