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Automatic Climate Control, Acc: Overview Saab 9-5 II

Automatic HVAC System ~3317 words

Automatic HVAC Description and Operation

The air temperature and the air delivery description and operation are divided into eight areas

  1. HVAC Control Components
  2. Air Speed (Front)
  3. Air Speed (Rear)
  4. Air Delivery (Front)
  5. Air Delivery (Rear)
  6. Heating and A/C Operation
  7. Recirculation Operation
  8. Automatic Operation
  9. Engine coolant
  10. A/C Cycle

Heating and A/C Operation

The purpose of the heating and A/C system is to provide heated and cooled air to the interior of the vehicle. The A/C system will also remove humidity from the interior and reduce windshield fogging. Regardless of the temperature setting, the following can affect the rate that the HVAC system can achieve the desired temperature

  1. Recirculation actuator setting
  2. Difference between inside and desired temperature
  3. Blower motor speed setting
  4. Mode setting

Only LLU

If the A/C or AUTO switch is depressed, the HVAC control module is permitted to request engagement of the A/C compressor and to connect IN the LED in the depressed switch. The HVAC control module transmits a message to the engine control module requesting engagement of the A/C compressor. The ECM grounds the compressor relay so that its internal contacts close and connect the compressor clutch solenoid to the battery voltage. The A/C compressor's diode prevents the voltage spike, that occurs when the solenoid's magnetic field collapses when the compressor is disengaged, from reaching the vehicle electrical system.

Only LAU, LBR, LBS, LBY, LDK or LHU

When the A/C switch or the AUTO switch is pressed, the HVAC control sends a signal to the HVAC control module via the LIN-Bus. The HVAC control module evaluates this signal and sends an A/C request signal to the ECM via the CAN-Bus. The ECM checks all preconditions before it gives its approval. If all conditions are met, it sends a release signal back to the HVAC control module. The A/C compressor is activated by the HVAC control module, which supplies battery voltage to the A/C compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width modulation (PWM) signal to the A/C compressor in order to command the performance of the A/C compressor. The performance of the A/C compressor is regulated according to adjusted interior temperature on the basis of characteristic lines. Therefore the HVAC control module grounds the A/C compressor with the PWM signal.

The following conditions must be met in order to activate the A/C compressor

  1. Battery voltage is between 9-18 V
  2. Engine coolant temperature is less than 120°C (248°F)
  3. Engine speed is greater than 600 RPM
  4. Engine speed is less than 5 500 RPM
  5. A/C high side pressure is between 230-3 100 kPa (33-449 PSI)
  6. Throttle position is less than 100%
  7. Evaporator temperature is greater than 2°C (36°F)
  8. ECM does not detect immoderate torque load
  9. ECM does not detect insufficient idle quality.
  10. The ambient temperature is above 0°C (32°F)

The sensor information is used by the ECM to determine the following

  1. The A/C high side pressure
  2. An A/C system load on the engine
  3. An immoderate A/C high side pressure
  4. The heat load at the A/C condenser

The air streams into the passenger compartment through the heater core and the evaporator core. The air temperature actuator drives the mixed air flap to induce the airflow. If the interior temperature should be increased, the mixed air flap is put into the position in which more air streams through the heater core. If the interior temperature should be decreased, the mixed air flap is put into the position in which more air streams through the evaporator core.

Recirculation Operation

The recirculation switch is integrated into the Radio/HVAC control. The selected recirculation switch position is sent to the HVAC control module via LIN-Bus. The HVAC control module controls the air intake through the air inlet actuator and recirculation actuator. In the recirculation mode the air inlet flap closes and the recirculation flap opens in order to circulate the air within the vehicle. In fresh air mode the air inlet flap opens and the recirculation flap is closed again in order to route outside air into the vehicle.

In automatic mode the values of the windshield temperature and inside moisture sensor are used as control inputs for the HVAC control module application to calculate the fog risk on passenger compartment side of the windshield compartment side. The A/C compressor and the defrost mode are activated to prevent or remove fog on the passenger compartment side of the windshield.

Automatic Operation

In automatic operation, the HVAC control module maintains the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and recirculation actuator.

To put the HVAC system in automatic mode, the following is required

  1. The auto switch must be activated.
  2. The air temperature switches must be in any other position than full hot or full cold position.

Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators automatically adjust to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature

  1. Monitors the following sensors: Ambient Air Temperature Sensor Lower left air temperature sensor Lower right air temperature sensor Lower rear air temperature sensor (only CJ4) Upper left air temperature sensor Upper right air temperature sensor Upper rear air temperature sensor (only CJ4) Windshield Temperature and Inside Moisture Sensor Ambient Light/Sunload Sensor
  2. Regulate the blower motor speed
  3. Regulate the rear blower motor speed (only CJ4)
  4. Position the air temperature actuators
  5. Position the rear air temperature actuators (only CJ4)
  6. Position the mode door actuator
  7. Position the rear mode door actuator (only CJ4)
  8. Position the recirculation actuator
  9. Position the air inlet actuator
  10. Request A/C operation
  11. Control of the A/C compressor (only LAU, LBR, LBS, LBY, LDK or LHU)

When the warmest position is selected in automatic operation the blower speed will increase gradually until the vehicle reaches normal operating temperature. When normal operating temperature is reached the blower stays on high speed and the air temperature actuators stays in the full heat position.

When the coldest position is selected in automatic operation the blower stays on high and the air temperature actuators stay in full cold position. The mode actuator remains in the panel position and the recirculation actuator will remain in the recirculation position.

Under cold ambient temperatures, the automatic HVAC system provides heat in the most efficient manner. The operator can select an extreme temperature setting but the system will not warm the vehicle any faster. Under warm ambient temperatures, the automatic HVAC system also provides air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.

In automatic mode the values of the windshield temperature and inside moisture sensor are used as control inputs for the HVAC control module application to calculate the fog risk on the passenger compartment side of the windshield and ability to reduce fuel consumption by decreasing A/C compressor power to a minimum without causing any fog. The A/C compressor and the defrost mode are activated to prevent or remove fog on the passenger compartment side of the windshield.

Circuit/System Description

The ambient light/sunload sensor includes the sunload sensor and passenger compartment temperature sensor.

This sensor assembly provides information about

  1. Sun heat intensity
  2. Elevation
  3. Azimuth
  4. Passenger compartment temperature

The sunload sensor is connected to ground and to a 12 V clocked power supply through the HVAC control module. This clocked power supply is to power the sensor electronics and to work as a clock generator to the sunload sensor micro controller. The sensor uses a pulse signal for data identification and transferring the sun intensity measurement. At each positive transition from the clocked supply input, the sunload sensor micro controller will shift channels enabling new intensity measurement on the signal output to the HVAC control module. The signal voltage varies between 0-4 V.

The passenger compartment temperature sensor is a negative temperature co-efficient thermistor. A signal and low reference circuit enables the sensor to operate. When the air temperature increases, the sensor resistance decreases. The sensor signal varies between 0-5 V.

Bright or high intensity light causes the vehicles interior temperature to increase. The HVAC system compensates for the increased temperature by diverting additional cool air into the vehicle.

Description and Operation

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The air temperature sensors are a 2-wire negative temperature co-efficient thermistor. The vehicle uses the following air temperature sensors

  1. Air Temperature Sensor - Left Upper
  2. Air Temperature Sensor - Left Lower
  3. Air Temperature Sensor - Right Upper
  4. Air Temperature Sensor - Right Lower
  5. Air Temperature Sensor - Rear Upper (Only With CJ4)
  6. Air Temperature Sensor - Rear Lower (Only With CJ4)
  7. A/C Evaporator Temperature Sensor

A signal and low reference circuit enables the sensor to operate. As the air temperature surrounding the sensor increases, the sensor resistance decreases. The sensor signal voltage decreases as the resistance decreases. The sensor operates within a temperature range between -40 to +85°C (-40 to +185°F). The sensor signal varies between 0-5 V. The HVAC control module converts the signal to a range between 0-255 counts. As the air temperature increases the count value will decrease. If the HVAC control module detects a malfunctioning sensor, then the control module software will use a default air temperature value. The default action ensures that the HVAC system can adjust the inside air temperature near the desired temperature until the condition is corrected.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The windshield temperature and inside moisture sensor includes the relative humidity sensor, windshield temperature sensor and humidity sensing element temperature sensor.

This sensor assembly provides information about

  1. Relative humidity level at windshield inside
  2. Temperature of the windshield inside
  3. Temperature of the humidity sensor element

The relative humidity sensor measures the relative humidity of the compartment side of the windshield. It also detects the temperature of the windshield surface on the compartment side. Both values are used as control inputs for the HVAC control module application to calculate the fog risk on windshield compartment side and ability to reduce fuel consumption by decreasing A/C compressor power to a minimum without causing any fog. The sensor will also enable partial recirculation mode in order to improve heat-up performance of the passenger compartment under cold ambient temperature conditions without the risk of mist build-up on the windshield. The humidity sensor element temperature sensor supplies the temperature of the humidity sensor element. It is only needed if the thermal contact between the humidity sensing element and the inside windshield surface is not sufficient.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control from the HVAC control module, battery positive and ground circuits enable the blower motor control module to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower motor control module in order to command the blower motor speed. The blower motor control module transfers the PWM signal into a corresponding blower motor voltage. The voltage resides between 2-13 V and changes linear to the height of the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The blower motor control module - auxiliary is an interface between the HVAC control module and the blower motor. The Blower Motor Speed Control from the HVAC Control Module, battery positive and ground circuits enable the Blower Motor Control Module - Auxiliary to operate. The HVAC Control Module provides a Pulse Width Modulation (PWM) signal to the Blower Motor Control Module - Auxiliary in order to command the blower motor speed. The blower motor control module - auxiliary transfers the PWM signal into a corresponding blower motor voltage. The voltage resides between 2-13 V and changes linear to the height of the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

Stepper motors are used for temperature regulation, air distribution control and recirculation flap control.

With the appropriate switches at the Radio/HVAC control, the desired air temperature flap position, air distribution flap position and recirculation flap position can be put in. The selected values are passed to the HVAC control module via the LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motors and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motors put the appropriate flap into the calculated position, in order to reach the put in temperature/position.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The HVAC control module sends a pulse width modulation (PWM) signal to the electrical auxiliary heater, if the interior temperature is too low and additional heat is requested. The request signal from the HVAC control module, battery positive, ignition and ground circuits enable the electrical auxiliary heater to operate. Through the signal circuit the electrical auxiliary heater sends via a PWM signal the current status to the HVAC control module.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The HVAC control module detects exhaust gas by an air quality sensor. The air quality sensor is a 3-wire sensor with an ignition voltage circuit, a ground circuit and a signal circuit.

The information is pulse width modulation (PWM) signal generated on the output pin.

The HVAC control module evaluates the information of the air quality sensor and closes the recirculation flap while in the automatic mode as soon as the concentration of pollutants exceeds a preset value.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The HVAC control module supplies battery voltage to the A/C compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width modulation (PWM) signal to the A/C compressor in order to command the performance of the A/C compressor. The performance of the A/C compressor is regulated according to adjusted interior temperature on the basis of characteristic lines. Therefore the HVAC control module grounds the A/C compressor with the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The engine control module (ECM) monitors the high side refrigerant pressure through the A/C refrigerant pressure sensor. The ECM supplies a 5V reference and a low reference to the sensor. Changes in the A/C refrigerant pressure cause the sensor signal to the ECM to vary. When the pressure is high, the signal voltage is high. When the pressure is low, the signal voltage is low. When pressure is high, the ECM commands the cooling fans on. When pressure is too high or too low, the ECM will not allow the activation of the A/C compressor.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

When the A/C switch is pressed, the HVAC control module sends an A/C request signal to the engine control module (ECM) via the CAN bus. The ECM therefore grounds the A/C compressor clutch relay control circuit, which activates the clutch relay. Battery voltage is supplied via the relay contacts to the A/C compressor clutch which is then activated.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The HVAC control module supplies battery voltage to the A/C compressor. When the A/C switch is pressed, the HVAC control module provides a pulse width modulation (PWM) signal to the A/C compressor in order to command the performance of the A/C compressor. The performance of the A/C compressor is regulated according to adjusted interior temperature on the basis of characteristic lines. Therefore the HVAC control module grounds the A/C compressor with the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

When the A/C switch is pressed, the HVAC control module sends an A/C request signal to the engine control module (ECM) via the CAN bus. The ECM therefore grounds the A/C compressor clutch relay control circuit, which activates the clutch relay. Battery voltage is supplied via the relay contacts to the A/C compressor clutch which is then activated.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control from the HVAC control module, battery positive and ground circuits enable the blower motor control module to operate. The HVAC control module provides a pulse width modulation (PWM) signal to the blower motor control module in order to command the blower motor speed. The blower motor control module transfers the PWM signal into a corresponding blower motor voltage. The voltage resides between 2-13 V and changes linear to the height of the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The blower motor control module - auxiliary is an interface between the HVAC control module and the blower motor - auxiliary. The Blower Motor Speed Control from the HVAC Control Module, battery positive and ground circuits enable the Blower Motor Control Module - Auxiliary to operate. The HVAC Control Module provides a Pulse Width Modulation (PWM) signal to the Blower Motor Control Module - Auxiliary in order to command the blower motor speed. The blower motor control module - auxiliary transfers the PWM signal into a corresponding blower motor voltage. The voltage amounts to between 2-13 V and changes linear to the reading of the PWM signal.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

With the temperature switches at the Radio/HVAC control, the wished air temperature flap position can be put in. The selected values are sent to the HVAC control module via LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motors and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motors put the mixed air flaps into the calculated position, in order to reach the put in temperature.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

With the temperature switches at the Radio/HVAC control - auxiliary, the desired air temperature flap position can be put in. The selected value is sent to the HVAC control module via the LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the mixed air flap into the calculated position, in order to reach the selected temperature.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

With the defrost switch, air to foot well switch, air to windscreen switch and the air to head area switch at the HVAC control, the wished air distribution flap position can be put in. The selected value is sent to the HVAC control module via the LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the air distribution flap into the selected position.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

With the MODE switch at the Radio/HVAC control - auxiliary, the wished air distribution flap position can be put in. The selected value is sent to the HVAC control module via the LIN-Bus. The HVAC control module supplies a 12 V reference voltage to the stepper motor and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the air distribution flap into the selected position.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

The desired position of the recirculation flap can be set with the recirculation switch at the Radio/HVAC control. The selected value is passed to the HVAC control module via LIN-Bus. Two stepper motors are used for recirculation and fresh air control. The first stepper motor moves the air inlet flap, the second stepper motor moves the recirculation flap. In the recirculation mode the air inlet flap closes and the recirculation flap opens in order to circulate the air within the vehicle. In fresh air mode the air inlet flap opens and the recirculation flap is closed again in order to route outside air into the vehicle. The HVAC control module supplies a 12 V reference voltage to both stepper motors and energizes the appropriate 4 stepper motor coils with a pulsed ground signal. The stepper motor puts the recirculation flap and fresh air flap into the selected position.

AUTOMATIC HVAC DESCRIPTION AND OPERATION

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