HVAC Control Components
HVAC CONTROL MODULEAir Temperature Description And Operation:
The HVAC control module (IPM) is a class 2 device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for Keep Alive Memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The Dash Integration Module (DIM), which is the vehicle power mode master, provides a device on signal. The control module (IPM) supports the features.
PERSONALIZATION
The HVAC control module (IPM) will receive information that defines the current driver of the vehicle from the Driver Door Module (DDM) through class 2 communication. The HVAC system will memorize the following system configurations for up to two unique drivers:
^ Driver set temperature
^ Passenger set temperature
^ Mode
^ Blower motor speed
^ A/C compressor request, auto ON or A/C OFF
This information shall be stored inside the HVAC control module (IPM) memory. When a different driver identification button is selected the HVAC control module will recall the appropriate driver settings. When the HVAC control module (IPM) is first turned on, the last stored settings for the current driver will be activated except for the rear defrost and heated seat settings.
AIR TEMPERATURE ACTUATORS
The air temperature actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.
AIR TEMPERATURE SENSORS
Air Temperature Description And Operation:
The air temperature sensors are 2 wire negative temperature Co-efficient thermistors. The vehicle uses the following air temperature sensors:
^ Ambient
^ Inside
^ Upper right
^ Upper left
^ Lower right
^ Lower left
The upper and lower duct sensors are divided into left and right zone operation. The left side upper and lower duct sensors will only effect the operation of the left air temperature actuator and the right side upper and lower duct sensors will only effect the operation of the right air temperature actuator. The duct sensors are used to measure the temperature of the air exiting the ducts. The sensors operate within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). When temperature increases the sensor signal decreases.The HVAC control module converts the 0-5 volt sensor signal to a range between 0-255 counts. If the HVAC control module (IPM) detects that one of the duct temperatures must change, the HVAC control module (IPM) will adjust the appropriate air temperature actuator. The list shows the duct sensors that are monitored by the HVAC control module in each mode position.
If the HVAC control module (IPM) detects a malfunctioning sensor, the HVAC system will only malfunction when the sensor is monitored.
The inside temperature sensor operates within a temperature range between -6.5°C (20.3°F) to 57.5°C (135.5°F). A fan located internally to the inside air temperature sensor housing continually draws passenger compartment air over the sensor. If the internal fan is inoperative the inside air temperature will change very slowly. If the sensor is shorted to ground, the system will operate in the maximum cooling mode. If the sensor is shorted to voltage or open, the system will operate in the maximum heating mode.
The ambient sensor operates within a temperature range between -30°C (-22°F) to 51°C (123.8°F). If the HVAC control module (IPM) has determined that the outside temperature sensor has failed, the Driver Information Center (DIC) display shall display "59°F" in place of the outside air temperature. If the sensor is shorted to ground, the system will operate in the maximum cooling mode. If the sensor is shorted to voltage or open, the system will operate in the maximum heating mode. If the engine coolant temperature is not more than 28°C (50°F) above the sensor reading, or if the engine has not been started in two hours, then the actual ambient air temperature sensor reading is displayed. The ambient air temperature displayed may be allowed to increase after 80 seconds as long as the vehicle speed is greater than 32 km/h (20 mph), but only at a slow, filtered rate. If the sensor reading is ever less than the displayed value or if the vehicle speed is 72 km/h (45 mph) or greater, then the ambient air temperature changes are displayed as rapidly as possible.
SUNLOAD SENSOR
The sunload sensor is a 2 wire photo diode. The vehicle uses left and right sunload sensors. Low reference and signal circuits enable the sensor to operate. As the sunload increases, the sensor signal decreases. The sensor operates within an intensity range between completely dark and bright. The sensor signal varies between 0-5 volts. The HVAC control module converts the signal to a range between 0-255 counts.
The sunload sensor provides the HVAC control module a measurement of the amount of light shining on the vehicle. Bright, or high intensity, light causes the vehicles inside temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle. If sensor is open, no sunload condition occurs. If sensor is shorted, maximum sunload condition occurs with increased cooling mode.
A/C REFRIGERANT LOW TEMPERATURE SENSOR
The dash integration module (DIM) monitors the sensor to determine low side pressure based on the pressure to temperature relationship of the R134a. This sensor is located on the low side line. The sensor is used to cycle the A/C compressor ON and OFF to prevent the evaporator core from freezing. A thermistor inside the sensor varies its resistance to monitor the temperature of the freeon. The DIM monitors the voltage drop across the thermistor when supplied with a 5 volt reference signal. The DIM will send a class 2 message to the PCM to stop requesting the A/C compressor clutch operation if the temperature drops below 2°C (28°F). Vehicles operating above 32 km/h (20 mph) will be controlled to a minimum ON time of 46 seconds before the DIM will allow the clutch to disengage. The sensor must be above 10°C (50°F) before the DIM will request A/C compressor clutch operation again.
The sensor operates within a temperature range between -40°C (-40°F) to 215°C (-355°F). If the DIM detects an open in the A/C refrigerant low temperature sensor or circuit, the class 2 message sent to the PCM will not allow A/C operation. The HVAC control module (IPM) will then send a request to the Radio for display of the "SERVICE A/C SYSTEM" that will be displayed on the DIC. The HVAC control module (IPM) will also display A/C OFF on the module as long as the condition is present.
A/C REFRIGERANT PRESSURE SENSOR
The A/C refrigerant pressure sensor is a 3 wire piezoelectric pressure transducer. A 5 volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The A/C refrigerant pressure sensor prevents the A/C system from operating when an excessively high or low pressure condition exists. The PCM disables the compressor clutch under the following conditions:
^ A/C pressure is more than 2850 kPa (413 psi). The clutch will be enabled after the pressure decreases to less than 1750 kPa (254 psi).
^ A/C pressure is less than 204 kPa (30 psi). The clutch will be enabled after the pressure increases to more than 220 kPa (32 psi).
If the PCM detects a failure in the A/C refrigerant pressure sensor or circuit, the class 2 message sent to the HVAC control module (IPM) will be invalid. The HVAC control module (IPM) will then send a request to the Radio for display of the "SERVICE A/C SYSTEM" that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.