Automatic Climate Control

PROGRAM NUMBER
The program number is a number calculated by the Air Conditioning Programmer (ACM) to express the amount of heating or cooling required to meet the desired In-Vehicle temperature. This number is based on the following variables.
^ Set temperature on climate control center.
^ Outside temperature.
^ In-Vehicle air temperature.
^ Sun Load sensor.

The calculated program number is used to determine the air delivery mode and blower speed, and is a factor in determining the air mix valve position. A program number of "0" represents maximum system cooling and "255" represents maximum system heating. As the In-Vehicle air temperature nears the set temperature, the program number will begin to approach a value for maintaining comfort.

The program number can be observed with the use of the Scan Tool.

AIR MIX VALVE POSITION
The proper air mix valve position is determined by the ACM. In order to provide the proper mix of warm and cool air, the ACM monitors the following variables:
^ Set temperature.
^ Coolant temperature.
^ Outside temperature.
^ Air delivery mode.
^ In-vehicle air temperature.
^ Engine RPM.
^ Low side temperature.
^ Blower speed.
^ Sun load sensor.
^ Mix motor feedback.

Based upon these inputs, the ACM can position the air mix valve for the appropriate blend of air through the evaporator core and heater core depending upon the current program number.

BLOWER SPEED CONTROL
For every given program number and climate control panel setting, the ACM has a calculated blower speed.

The console rear blower speed is controlled manually by a direct power feed. The variable speed is controlled by a resistor which varies the voltage to the blower motor at each setting. The ACM monitors the feedback for diagnosis.






AIR DELIVERY MODE CONTROL
The various settings discussed in this section are used to provide comfortable heating or cooling. The ACM 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 rear air outlets receive air flow during all modes as well; however, the vents may be shut "OFF" if desired by the "VENT" dial located on the rear of the console. Based on the current program number and control center setting the ACM determines the air delivery mode. The following delivery modes are possible.

Max A/C Mode
Air is distributed to the A/C outlets with bleed to heater outlets. Air inlet valve slowly opens if "AUTO" is selected which provides 90% recirculated air. In "ECON" this valve will remain closed and provide only outside air.

A/C Mode
Air is delivered to the A/C outlets with bleed air flow to the heater outlets. If previously in "AUTO-MAX A/C" mode, air inlet valve will slowly close to provide 100% outside air.

Bi-Level Mode
Air is dispensed through the A/C outlets and heater outlets. This mode is used to transition from A/C to heater mode or vice-versa.

Heater Mode
Air flow is delivered by the heater outlets with bleed to defrost outlets.

Defog Mode
This mode splits the air between the heater (floor ducts) and defroster. The A/C clutch is enabled if outside temperature is above 40°F to help dehumidify the interior.

This mode can be entered manually by pressing the "DEFOG" button on (C68) equipped vehicles.

Off Mode
With the system "OFF," the blower will remain "OFF" 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
Air flow is sent to the defroster outlets with bleed to heater outlets. This mode is not remembered after the key is turned "OFF" The system will switch to the "AUTO" selection if "FT DEF" was previously active. If the operator selects "FT DEF" while the outside temperature is below -4°C (25°F), the ACM will limit the blower to 7 volts until the coolant has been above 36°C (97°E) for three 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.

IPC Cooling Mode
Under certain conditions, the blower will turn "ON" and direct air to the A/C vents to cool the Instrument Panel Cluster (IPC) to prevent damage to IPC electronic components. IPC cooling mode will be enabled with:
^ Ignition in RUN position.
^ Engine is not running or HVAC OFF
^ In-Vehicle temperature greater than 51°C (125°F.
^ Blower override modes are not operating.

Once enabled, minimum run time is four minutes. IPC cooling mode is disabled if:
^ In-Vehicle temperature is less than 50°C (121°F) or engine is running and HVAC is not "OFF."
^ Engine is running.
^ Diagnostics is entered or if a PCM-IPC serial data fault is present.

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, 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.
Operator selection of the "AUTO" mode will prevent the purge modes from initiating. The purge modes will only be initiated if the system is operated in a manual mode.
The "A/C" purge cannot be restarted and will be disabled for the entire ignition cycle.

Normal Purge
If the system is "ON" and in "AUTO" 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 A/C outlets which prevents any moist air from reaching the windshield. To further purge ducts of moist air, the ACM 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 outside temperature), the ACM will automatically resume normal operation.

Cold Purge
If the system is turned "ON" in any mode with "HIGH" blower when the coolant temperature is below 15°C (59°F), cold purge is enabled. 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 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 outside temperature), the ACM will automatically resume normal control.

A/C Purge
If the system is "ON" and in "AUTO" mode, except "DEFOG," "OFF", or "HIGH" blower, the program number would result in cooling or intermediate modes, and the conditions for COLD PURGE or NORMAL PURGE are not present, A/C PURGE will be enabled. 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 ACM will automatically resume normal air mode delivery control once the A/C PURGE is completed.