Heating And Cooling - Honda Prelude 1990 Online Reference Owner's Manual

The vents, heater and air conditioner are combined in one system;
adjusting four basic controls to different settings can provide a full
range of interior temperatures for safe and comfortable driving,
(Air conditioner is optional on the 2.0 S and 2.0 Si models.)
Ventilation
The flow-through ventilation system can provide fresh air to the
interior when the car is moving or stopped, even with the sunroof
and windows closed.
NOTE:
For proper air flow, the flow-through vents must not be covered.
Keep the air inlet at the base of the windshield free of leaves or
other debris.
AIR INLET
You can adjust the controls to direct cool or warm outside air
throughout the car for defogging windows, heating, or cooling by
turning on the fan.

Heating and Cooling

AIR OUTLET
AIR OUTLET
(cont'd)