Purge Modes

Three purge modes, which are not represented in the system response chart, occur when the system is first turned ON but only if certain conditions exist. Each of the purge modes is designed to improve comfort and reduce the possibility of windshield fogging. In the purge modes, airflow is redirected at a reduced blower speed until conditions permit normal control to be resumed. The purge modes are also used to delay heater blower turn ON and to prevent cool air from exiting the heater outlets.

Operator selection of any mode but AUTO mode will prevent the purge modes from initiating. The purge modes will not be initiated if the system is operated in a manual mode.

Normal Purge

In normal purge, the blower is turned OFF and any airflow is directed to the heater outlets with bleed to A/C outlets which prevents any moist air from reaching the windshield. To further purge ducts of moist air, the heater and A/C programmer will operate at low blower for several seconds just prior to resuming normal operation. Normal operation will resume preceded by this low blower period after either of the following conditions exist:

^ Program number would result in cooling.
^ Coolant temperature is above 36°C (97°F).

If neither of these conditions exist within approximately one to four minutes (depending upon ambient temperature), the heater and A/C programmer will automatically resume normal operation.

Cold Purge

In cold purge, the blower will be powered low and the airflow will be directed to the front defrost outlets to keep breath humidity off of the windshield. Normal operation will resume several seconds after one of the following conditions exist:

^ Program number would result in cooling.
^ Coolant temperature is above 36°C (97°F).

If neither of these conditions exist within approximately one to four minutes (depending upon ambient temperature), the heater and A/C programmer will automatically resume normal control.

A/C Purge

In A/C PURGE, the blower will be operated at a medium speed for four seconds with the air primarily directed out the heater outlets.

During the A/C PURGE, the hot moist air will be purged from the A/C module and ducts to the floor while the evaporator begins to cool the incoming air. The heater and A/C programmer will automatically resume normal air mode delivery control once the A/C PURGE is completed.