Climate Control System - General Information and Diagnostics

SYSTEM AIRFLOW DESCRIPTION

MAX A/C
When MAX A/C is selected:
- The air inlet blend door is at full vacuum, closing off outside air and allowing only recirculated air.
- The defrost blend door is at full vacuum while the footwell blend door is at no vacuum, closing both doors.
- The vent/register blend door is at partial vacuum, directing airflow to the driver side, passenger side and center registers.
- Temperature control is usually set for maximum cold but may be heated if selected.
- Air is picked up at the recirculation opening by the blower motor. With the temperature control set for maximum cold, air flows across the A/C evaporator core, diverting past the heater core, and is then directed into the passenger compartment through the driver side, passenger side and center registers.
- The A/C compressor is enabled.
- The blower motor is ON.

A/C
When A/C is selected:
- The air inlet blend door is at no vacuum, blocking the recirculation passage and admitting outside air.
- All other door positions are the same as described under MAX A/C.
- The temperature setting can be changed manually.
- The A/C compressor is enabled.
- The blower motor is ON.

PANEL
When PANEL is selected:
- The air inlet blend door, with no vacuum being applied, blocks recirculated air and allows outside air. Air flows through the system to the driver, passenger and center registers.
- The vent/register blend door is at partial vacuum to direct airflow to the driver, passenger and center registers.
- The defrost blend door is at full vacuum and the defrost airflow door is at no vacuum, closing off airflow to the windshield defroster hose nozzles and footwell ducts.
- The temperature setting can be changed manually to heat the air, but air cannot be cooled below the outside temperature.
- The A/C compressor is disabled when VENT is selected.
- The blower motor is ON.

PANEL/FLOOR
When PANEL/FLOOR is selected:
- The air inlet blend door is at no vacuum, blocking the recirculation passage and allowing outside air.
- The footwell blend door and the panel airflow door are in the full vacuum position, allowing airflow to blend between the panel vents and the footwell ducts.
- The defrost airflow door is at full vacuum, closing off airflow to the windshield defroster hose nozzle and directing airflow to the heater outlet footwell duct.
- The A/C compressor is disabled.
- The blower motor is ON.

OFF
When OFF is selected:
- The air inlet blend door is at full vacuum, closing off outside air and allowing only recirculated air.
- The vent/register blend door and the defrost, footwell and blend airflow doors are at no vacuum, closing off the passages to the driver, passenger and center registers.
- The blower motor and the A/C compressor are off.

FLOOR
When FLOOR is selected:
- The air inlet blend door is at no vacuum, blocking recirculated air and allowing outside air.
- The footwell airflow door is at the full vacuum position, opening the door and allowing airflow through the footwell ducts.
- The defrost airflow door and the vent/register blend door are in the no vacuum position, closing off airflow to the windshield defroster hose nozzles and driver, passenger and center registers.
- The temperature control can be positioned to mix air flowing through and around the heater core achieve the selected temperature level.
- The A/C compressor is disabled.
- The blower motor is ON.

FLOOR/DEFROST
When FLOOR/DEFROST is selected:
- The air inlet blend door is in the no vacuum position, blocking recirculated air and allowing outside air.
- The footwell blend door is at full vacuum allowing air to flow through the footwell ducts.
- The defrost blend door is at no vacuum, allowing airflow to both the windshield defroster hose nozzle and side window demister hose nozzle ducts.
- The vent/register blend door is at no vacuum.
- The A/C compressor is enabled to dehumidify the air and reduce windshield fogging.
- The blower motor is on.

DEFROST
When DEFROST is selected:
- The air inlet blend door is at no vacuum, allowing outside air to enter the system.
- The defrost blend door is at no vacuum, directing the airflow to the windshield through the defroster ducts and the side windows through the demister ducts.
- The panel airflow door and the footwell airflow door are at no vacuum, so that most of the incoming air is directed to the windshield defroster hose nozzle. There is also airflow to the side window demister and hose.
- The temperature control knob setting determines the amount of air that is directed through the heater core and the amount that bypasses the heater core.
- The A/C compressor is enabled to dehumidify the air and reduce windshield fogging.
- The blower motor is on.

Air Distribution
There are 2 sources of air available to the air distribution system:
- Outside air
- Recirculated air

Recirculated air is only used when the manual climate control mode selector is set in the MAX A/C or OFF modes.

Air distribution within the vehicle is determined by the function selector switch position. Airflow control doors are used to direct airflow within the A/C evaporator housing and heater. Vacuum control motors are used to position these airflow control doors.

The air distribution system is designed to provide airflow from the defrost nozzle when no vacuum is applied to any of the vacuum control motors. This is done to prevent a situation where defrost cannot be obtained due to a system vacuum leak.

Air enters the passenger compartment from the:
- instrument panel register.
- heater outlet floor duct.
- windshield defroster hose nozzle.
- side window demisters.
- rear footwell duct.

Passenger compartment air is exhausted from the vehicle through open windows or through the air extractors located in the rear of the vehicle.

Refrigerant System Dye
Fluorescent refrigerant system dye is added to the refrigerant system at the factory to assist in refrigerant system leak diagnosis using an approved ultraviolet blacklight. It is not necessary to add additional dye to the refrigerant system before diagnosing leaks, even if a significant amount of refrigerant has been removed from the system. New suction accumulators are shipped with a fluorescent dye wafer included in the desiccant bag which dissolves after approximately 30 minutes of continued A/C operation. It is not necessary to add dye after flushing or filtering the refrigerant system because a new suction accumulator is installed as part of the flushing or filtering procedure. Additional refrigerant system dye should only be added if more than 50% of the refrigerant system lubricant capacity has been lost due to a fitting separation, hose rupture or other damage. Refer to Fluorescent Dye Leak Detection. Fluorescent Dye Leak Detection

Control Components

Manual Climate Control
The manual climate control components are used to select:
- air inlet source (outside or recirculated).
- blower motor speed.
- discharge air temperature (temperature blend).
- discharge air location (DEFROST, PANEL, FLOOR).
- A/C compressor operation.

Control System Inputs
The climate control assembly has 3 system control inputs.

Function Selector Switch
The function selector switch combines a vacuum selector valve that determines air distribution and an electrical switch to supply battery voltage to the A/C compressor circuit and the blower motor circuit. When the function selector switch is in the MAX A/C, A/C, FLOOR/DEFROST or DEFROST positions, the A/C compressor will be operational. The function selector switch can be replaced separately from the climate control head unit.

Temperature Control Switch
The temperature control switch setting determines air temperature. Temperature selection is accomplished through a cable connected to the temperature blend door. Movement of the temperature control switch from COOL (blue) to WARM (red) causes a corresponding movement of the temperature blend door and determines the air discharge temperature that the air distribution system will maintain. A new temperature control switch can be installed separately from the climate control head unit.

Blower Motor Switch
The blower motor switch controls blower motor speed by adding or bypassing resistors in the blower motor switch resistor in all function selector switch positions except OFF. A new blower motor switch can be installed separately from the climate control head unit.

Control System Outputs

Blower Motor Resistor
The blower motor resistor:
- is located on the evaporator core housing behind the glove compartment.
- has 3 resistor elements mounted on the resistor board to provide 4 blower motor speeds.
- depending on the blower motor switch position, series resistance is added or bypassed in the blower motor circuit to decrease or increase the blower motor speed.
- has an overheating device (thermal limiter) that will open the resistor coil when the temperature reaches approximately 184 1|C (363 1|F), interrupting the blower motor operation in all speeds except high.
- is replaced as an assembly. The thermal limiter cannot be reset and cannot be repaired.

Temperature Blend Door Actuator
The temperature blend door actuator:
- is connected between the temperature control switch and the temperature blend door.
- moves the temperature blend door on the command of the temperature control switch.

Vacuum Control Motors
The vacuum control motors:
- direct system airflow to the vehicle interior as determined by the function selector switch.