AIR SPEED
The blower motor forces outside air into the vehicles interior. The vehicle operator determines the blower motors speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control assembly.
The blower motor OFF input is connected in series with the HVAC control assembly by the off blower motor control circuit. Depending upon the selected speed, power is provided to the blower motor from either the ignition voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control assembly by the ignition voltage and the ground circuits.
Low Speed Position
When the Low 1 blower speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
Medium Speed Positions
When the Medium (1) blower speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the medium (1) blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium (2) blower speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the medium (2) blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
When the Medium (3) blower speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the medium (3) blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.
High Speed Position
When the High blower speed is selected, the HVAC control assembly applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.
Off Position
The blower motor is turned off. When the vehicle is moving, air flowing over the vehicle increases the air pressure just ahead of the windshield. This forces air into the outside air inlet, into the HVAC assembly and out through the defrost outlets. The incoming air may be warmed but not cooled.
HVAC Control Module
The HVAC control assembly is powered up by the ignition voltage circuit. When the mode switch is rotated, a variable resistor in the HVAC control assembly changes the voltage on the mode door control circuit for an actuator position change. The module does not utilize Keep Alive Memory (KAM). The module does not have Class 2 communication.
Mode Actuator
The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control assembly sends signals to the mode door actuator through the mode door control circuit. Zero volts drives the actuator in one direction while 5 volts moves the actuator in the opposite direction. When the actuator receives 2.5 volts, the actuator rotation stops. A 5 volt reference signal is sent out over the 5 volt reference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control modules software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position
Panel (Vent)
When PANEL is selected, air is delivered through the instrument panel outlets with a small amount of air delivered to the floor. The mode actuator will retract, opening the panel door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.
Bi-Level
When BI-LEVEL is selected, air is delivered through the instrument panel outlets and to the floor outlets. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.
Floor
When FLOOR is selected, air is delivered to the floor outlets. The mode actuator will retract, closing the vent door. The defroster actuator will retract, closing the defroster door and open the heater door through mechanical linkage.
Defrost
When defrost is selected, the blower motor will be activated, regardless of the coolant temperature. The HVAC control assembly will override the auxiliary HVAC control assembly so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.
Recirculation Mode
The recirculation door will move automatically with an input from the A/C high pressure recirculation switch at approximately 350 psi (2413 kPa). The PCM will place the A/C system in recirculation mode when a signal is sent over the A/C refrigerant high pressure cut-out switch signal circuit. The recirculation actuator door control circuit is grounded by the PCM to ensure that the actuator is forced to the recirculation position. This allows for the cooler inside air to flow over the A/C evaporator and cool the refrigerant, until the high side pressure returns to normal. This action will allow the high side pressure to return to normal pressure at a faster pace. The recirculation door will move back to the outside air position when the high side pressure reaches 250 psi (1724 kPa).
Heater Only Option (C42)
On non-A/C equipped vehicles, the air temperature is controlled by moving the temperature knob. Moving the air temperature knob mechanically moves the air temperature door. They are linked together by the air temperature cable. The air temperature door position determines the amount of air directed to flow across the heater core. The recirculation mode will only be available when the HVAC control assembly is in Bi-Level mode only.
Intermittents
Intermittent faulty electrical connections or wiring may be the cause of intermittent conditions. Check for loose, bent or corroded terminals and terminal tension. Check for cut, bare or pinched wiring. Simulate the condition that is potentially causing the intermittent connection, either by wiggling the connections or the wiring, test driving or performing other operations while observing scan tool, DVOM or other testing equipment. See WIRING DIAGRAMS .
BLOWER CONTROLS SYSTEM CHECK
Turn ignition switch to ON position. Move blower speed selector switch from LOW to HIGH positions and listen for increase in blower motor speed at each switch position. Move blower speed selector switch from HIGH to LOW positions and listen for decrease in blower motor speed. If blower motor is inoperative in any or all speeds, see SYMPTOM TESTS .
DEFROSTER DOOR
Note. Vehicles without air conditioning do not have electric door actuators. The manufacturer does not separate "heater only" information from air conditioned vehicle information.
HEATER CORE
| CAUTION | Heater core can be damaged if too much force is applied to heater core pipes during hose removal. |
HEATER DOOR
Note. Vehicles without air conditioning do not have electric door actuators. The manufacturer does not separate "heater only" information from air conditioned vehicle information.
HVAC MODULE
Note. This applies to both heater only, and air conditioned vehicles. For heater only vehicles, disregard references to air conditioning checks and procedures.
MODE DOOR ACTUATOR
Note. Vehicles without air conditioning do not have electric door actuators. The manufacturer does not separate "heater only" information from air conditioned vehicle information.
Note. The mode actuator is located on the left side of the HVAC module.