"Dash vents" refers to the small openings or grids on the dashboard of a vehicle that release cool or warm air into the cabin, allowing the driver and passengers to adjust the temperature inside the car. Full definition
Set these test conditions: Engine set to 1800 rpm Recirulation air direction on Fan speed on low Windows up Temp set to max cold Air outlet to dash vents Vehicle in the shade Run for at least ten minutes, longer on a hot day. (mechanics.stackexchange.com)
The only consolation is a small rocker with a digital readout screen below the passenger - side dash vent that controls the temperature for that half of the cabin. (automobilemag.com)