Honda 1991 Prelude Owner's Manual page 49

Heating and Cooling (cont'd)
To Dehumidify with A/C (optional on the 2.0 Si model)
Because an air conditioner dehumidifies as it works, you can use it
in cool or cold weather to help defog the windows. Just switch the
fan on, push the A/C button on, select the desired function and
adjust the temperature lever to a comfortable setting.
NOTE:
This setting is desirable for most operating conditions in ambient
temperatures above approximately 32°F (0°C).
To Turn Everything OFF
Slide the temperature lever to the left, turn the fan switch off and
push the
NOTE:
This setting should only be used in cold weather for the first few
minutes of driving to prevent cold air from blowing into the cabin.
Under normal operating conditions, the fan should always be kept
ON to prevent the accumulation of stale air in the system.
button on.