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 improves comfort and reduces the possibility of windshield fogging. In the purge modes, the air flow is redirected at a reduced blower speed until conditions permit the resumption of normal control. The purge modes also control the following functions:

Operator selection of any mode, except the AUTO mode, prevents the purge modes from initiating. The purge modes will not initiate if the system operates in a manual mode.

In normal purge, the blower is turned OFF. Any airflow is directed to the heater outlets with bleed to the A/C outlets. This prevents moist air from reaching the windshield. In order to further purge the ducts of moist air, the heater and A/C programmer operates at low blower for several seconds prior to resuming normal operation. Normal operation will resume when either of the following conditions exist:

If neither of these conditions exist within approximately 1-4 minutes (depending upon the ambient temperature), the heater and A/C programmer automatically resumes normal operation.

In cold purge, the blower powers low. The air flow is directed to the front defrost outlets. This keeps the breath humidity off of the windshield. Normal operation resumes several seconds after one of the following conditions exist:

If neither of these conditions exist within approximately 1-4 minutes (depending upon the ambient temperature), the heater and A/C programmer automatically resumes normal operation.

In A/C PURGE, the blower operates at a medium speed for 4 seconds with the air primarily directed out of the heater outlets.

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