Mode Control Knob
WARNING: This page is about a different car, the 2004 Nissan Sentra. However, it is still accessible from the selected car via links, so may be relevant.
This control knob controls the outlet air flow.
When DEF or F/D mode is selected, the push control unit sets the intake door to FRESH.
The compressor turns on when DEF mode is selected and remains on until the key is turned off.