Air Delivery
The HVAC module incorporates most of the air conditioning components into one assembly The function of the air delivery system is to distribute air flow through the vehicle. the major components are the air inlet valve, blower motor, evaporator core, air mix valve, heater core, UP-DOWN valve and A/C - DEFROST valve.
The Electronic Control Module (ECM) 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 valve actuators. The Body Control Module (BCM) determines the proper air delivery mode based upon the current program number and control panel setting. The following delivery modes are possible.
MAX A/C MODE
A/C outlets with bleed to heater outlets. Air inlet valve slowly opens if "AUTO" is selected which provides 80% recirculated air. In "ECON" this valve will remain closed.
A/C MODE
A/C outlets with bleed to heater outlets. If previously in "AUTO" - Max A/C mode, air inlet valve will slowly close to provide 100% outside air.
INTERMEDIATE MODE
Defroster outlets with bleed to heater outlets. This mode is used to transition from A/C to heater mode or vice-versa. It will not occur if "HI FAN" is selected, in which case the system will go directly from A/C to heater or vice-versa.
"OFF" MODE
With the system at "OFF" the blower will remain off, however, any air which enters as the vehicle is moving will be directed the same as during the heater mode. The discharge air temperature will continue to be controlled by the air- mix valve.
FRONT DEFROST MODE
Defroster outlets with bleed to heater outlets. This mode is not allowed to remain after the key is turned off. The system will switch to the "AUTO" selection if "FRT. DEF." was previously active. If the operator selects "FRT. DEF." while the outside temperature is below -4°C (25°F), the BCM will limit the blower to 7 volts until the coolant has been above 43°C (1 10°F) for 3 minutes. This low blower voltage reduces the possibility of drawing snow through the air inlet. If the operator selects "HI FAN" while in this mode, the 7 volts blower limit will be overridden.
System Response Chart:
PURGE MODES
Two 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 reduce the possibility of windshield fogging, and increase comfort. In the purge modes, air flow 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.
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.