Air Delivery
Functional Test:
FUNCTION
The function of the air delivery system is to distribute air flow through the vehicle. The major components are the air inlet door, blower motor, evaporator core, air mix door, heater core, UP DOWN door and A/C - DEFROST door.
AIR DELIVERY MODE CONTROL
Various settings are used in order to provide comfortable heating or cooling. The Body Control Module (BCM) will direct the blended air in one of several air delivery modes. The side window outlets receive air flow during all modes of operation. The other outlets are directed air by commanding the programmer to energize specific vacuum solenoids feeding the appropriate combination of mode door actuators. The BCM determines the proper air delivery mode based upon the current program number and control panel setting.
PROGRAM NUMBER
The program number is a number calculated by the BCM to express the amount of heating or cooling required to meet the desired inside temperature. This number is based upon the following variables:
- Set temperature on Climate Control Panel (CCP).
- Outside temperature.
- In-car temperature.
- Sunload sensor.
The calculated program number is used to determine the proper air delivery mode and blower speed, and is a factor in determining the air mix door position. A program number of 0 represents maximum system cooling and 99 represents maximum system heating.
As the in-car temperature nears the desired set temperature, the program number will begin to approach a value appropriate for maintaining comfort based upon current ambient conditions.
The program number can be observed while in the diagnostic mode. Refer to Computers and Control Systems. Testing and Inspection
A self diagnostic feature allows the service technician to manually override the calculation of the program number to observe system operation throughout the working range.
COLD PURGE
If the system is turned on in any mode except "DEF" or "OFF", when the coolant temperature is below -2°C (28°F), cold purge is enabled.
In cold purge the blower will be off and any air flow will be directed to the front defrost outlets to keep breath humidity off the windshield. Normal operation will resume several seconds after either of the following conditions exist:
- Program number would result in cooling.
- Coolant temperature is above 43°C (110°F).
If neither of these conditions exist within approximately one to four minutes (depending upon outside temperature) the BCM will automatically resume normal control.
NORMAL PURGE
If the system is turned on in any mode except "DEF" or "OFF", when the program number would not result in cooling or intermediate modes and the conditions for cold purge do not exist, normal purge is enabled.
In normal purge the blower is turned off and any air flow is directed to the heater outlets with bleed to the A/C outlets which prevents any moist air from reaching the windshield. To further purge ducts of moist air the BCM 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 43°C (110°F).
If neither of these conditions exist within approximately one to four minutes (depending upon outside temperature) the BCM will automatically resume normal operation.