Use the system when the engine is running.
1. Press the button. 2. Adjust the temperature and the fan speed using the appropriate buttons. Select the air flow to the rear passenger compartment using the mode button. 3. To turn off the rear A/C, press the button again.
Honda Odyssey Service Manual > Rear A/C System Description: Rear Heater-A/C Door Positions HOTCOOL(VENT)(HEAT/VENT)(HEAT) ...