The heater and A/C programmer (HCM) can execute one of three purge modes when certain conditions exist. These are:
| • | Normal Purge |
| • | Cold Purge |
| • | A/C Purge |
When the system is powered up, it is desirable to purge the system of stale air and/or redirect it to avoid window fogging or other undesirable conditions. When the ignition is turned ON and the HVAC system is in the AUTO mode, the HCM will determine if any of the undesirable conditions exist. The HCM will then select the appropriate purge mode to minimize the undesirable condition.
Normal
Moisture tends to accumulate in the HVAC module assembly after the engine has been shut off. When the engine is restarted and the A/C system turns on this moisture may be expelled from the windshield or instrument panel outlets and cause window fogging.
On start-up the HCM checks for indications that this may occur. If the HCM determines that window fogging can occur, the mode actuator moves to the floor mode to direct most of the stale moist air to the floor for 10 seconds. The blower runs at low speed during normal purge. Normal purge mode is bypassed if any manual mode is chosen.
Cold
In cold weather, moist breath air from vehicle occupants may condensate on the windshield.
On cold engine start-up, the HCM checks for indications that this may occur. If so, the HCM positions the mode doors to direct air out of the windshield outlets and operates the blower.
Cold purge mode is bypassed if any manual mode is chosen.
A/C
Moisture tends to accumulate in the HVAC module assembly after the engine has been shut off. When the engine is restarted and the A/C system turns on, this moisture may be expelled from the instrument panel outlets toward the front seat occupants.
On start-up, the HCM checks for indications that this may occur. If so, the HCM positions the mode doors to direct air toward the floor and the instrument panel outlets. The blower motor operates at medium speed for 3 seconds.
A/C purge mode is bypassed if any manual mode is chosen.
