Purge Modes

The heater and A/C programmer can also access three additional purge modes when certain conditions exist.

When the system is powered up it is desirable to purge the system of stale air and/or redirect to avoid window fogging or other undesirable conditions. When the ignition is turned on and the HVAC system is in the AUTO or VENT mode, the programmer will determine if any of the undesirable conditions exist. The programmer then has the option of three different purge modes to select from in order to eliminate the undesirable condition.

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, this moisture may be expelled from the windshield or instrument panel outlets and cause window fogging.

On start-up, the programmer checks for indications that this may occur. If so, the programmer delays blower operation until the engine coolant temperature reaches 38°C (126°F), and closes the defroster door, positions the A/C door to direct air out the heater outlets, and runs the blower at low speed. The programmer then resumes normal system operation.

Normal purge mode is bypassed if the fan is operating in manual mode or any manual mode is chosen.

Cold Purge
In cold weather, moist breath air from vehicle occupants may condense on the windshield.

On cold engine start-up, the programmer checks for indications that this may occur. If so, the programmer positions the doors to direct air out the windshield outlets and operates the blower. The programmer then resumes normal system operation.

Cold purge mode is bypassed if the fan is operating in manual mode or any manual mode is chosen.

A/C 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, this moisture may be expelled from the instrument panel outlets toward front seat occupants.

On start-up, the programmer checks for indications that this may occur. If so, the programmer positions the A/C door to direct air toward the floor and operates the blower. The programmer then resumes normal system operation.

A/C purge mode is bypassed if the fan is operating in manual mode or any manual mode is chosen.