When the system is powered up, the heater and A/C programmer initiates one or both of the following functions to avoid window fogging or other undesirable conditions:
| • | Purge the system of stale air |
| • | Redirect the air |
The programmer will determine if any undesirable conditions exist when the ignition is turned on or the HVAC system is in AUTO or VENT mode.
The programmer has the option of 3 different purge modes to select from to eliminate undesirable conditions.
Normal Purge
Moisture tends to accumulate in the HVAC module after the engine has been shut off. When the engine is restarted and the A/C system turns on, the moisture may expel from the windshield or the instrument panel outlets. This causes window fogging.
On start-up, the programmer inspects for indications that window fogging may occur. If window fogging is evident, the programmer initiates the following functions:
| • | Delays the blower operation until the engine coolant temperature reaches 38°C (100°F) |
| • | Closes the defroster door |
| • | Positions the A/C door in order to direct the air out of the heater outlets |
| • | Runs the blower at low speed |
The programmer then resumes normal system operation.
Operating the fan in manual mode or selecting the manual mode will bypass normal purge mode.
Cold Purge
In cold weather, moist breath air from the vehicle occupants may condense on the windshield.
On cold engine start-up, the programmer inspects for indications that window fogging may occur. If window fogging is evident, the programmer initiates the following functions:
| • | Position the doors to direct air out the windshield outlets |
| • | Operate the blower |
The programmer then resumes normal system operation.
Operating the fan in manual mode or selecting the manual mode will bypass the cold purge mode.
A/C Purge
Moisture tends to accumulate in the HVAC module after the engine has been shut off. Moisture may expel from the instrument panel outlets toward the front seat occupants when the engine is restarted or when the A/C is turned ON.
On the start-up, the programmer inspects for indications of moisture. If moisture is evident, the programmer initiates the following functions:
| • | Positions the A/C door in order to direct the air toward the floor |
| • | Operates the blower |
The programmer then resumes the normal system operation.
Operating the fan in manual mode or selecting any manual mode will bypass the A/C purge mode.
