Actuators and Sensors

Actuators and Sensors (2 Zone Climate Control)

For the control of the fan and flaps the following actuators and sensors are in the air distribution housing and are used in 2 zone Climate Control:

- Evaporator Temperature Sensor
The evaporator temperature sensor will help avoid icing up of the air conditioning system. The sensor is about 20 mm behind the evaporator. With this distance to the evaporator, a homogenous air flow temperature can be measured at all temperature levels. The temperature behind the evaporator will be used as the basis for the electronic control valve for the AC. The cooling capacity of the compressor will be influenced depending on the "standard value" of the evaporator temperature sensor.

These standard values can be between 3 degrees C and maximum 12 degrees C and will be calculated using the following influences:
- lowest desired outgoing temperature and
- external temperature

The evaporator temperature sensor receives some foreign warmth due to the warmth emanating from the air distribution housing so that the temperature measured there will he up to 3 degrees C different than the actual evaporator temperature. This temperature difference is compensated for by a performance characteristic that is set in the control unit.

The following diagram shows the position of the various temperature sensors.







- Intake Air Temperature Sensor
The intake air temperature sensor is located directly in the intake line of the air distribution housing. Over the intake air sensor and the external temperature sensor, located near the front bumper, system external air is calculated. This (theoretical) external air temperature is taken into consideration in the automatic Climate Control. using this temperature value the compressor turns off at I < 2 degrees C (zero request) and the air volume (fan) changes. The front fan speed will be slightly increased at low system external temperatures.

Should the external temperature sensor fail, the function of the automatic climate control will still he maintained, hut will use only the value of the intake air temperature sensor.

- Internal Temperature Sensor
The temperature sensor, ventilated by a motor, is located right behind the slits in the control panel for the Climate Control and sucks air out of the internal area.
It is used as a control value with the vent temperature sensors (see the System Overview/Block Diagram) for the control of the temperature in the vehicle. The integrated air motor stops the measurement of residual heat. If the sensor or the ventilation motor is defective, an error will display in the error memory of the control module,

Sensor and vent motor are one unit.

- Air Quality Sensor
An air quality sensor (ceramic element) in the intake duct provides information with regards to hazardous values in the external air. It can be found in the motor area under the cover of the windshield wiper motor, right behind the air intake on the left side, The sensor reacts to nitrogen oxide (NOx), Carbon Monoxide (CO) and Sulphur Dioxide (SO2), in other words, vehicle exhaust gases. The sensor prompts a switch over to recirculation air.

- Pressure Sensor Climate Control
The pressure sensor is absolutely necessary as a measuring tool to evaluate the cooling system. It calculates the current pressure in the system and provides a PWM signal to the Climate Control module.

This signal is mainly used as a safety device to turn off the compressor when critical pressure exists.







This signal is also used to cause a condenser cooling from the DME. The need for the triggering of the condenser fan and the condenser cooling capacity is linearly based on the value received by the pressure sensor (see section "Condenser").







- Vent Temperature
The system offers the possibility of having a side control along with the internal temperature control cycle. The control module will calculate the various current values of the vent temperatures. The calculation of the temperatures will take place for each side separately over the temperature sensors (middle/side and floor vents) - shown in the block diagram. For these sensors there is a standard value in the control module that will be determined depending on the current position of the air distribution flap. This will create a standard value for each side and a current value. If the difference between the standard and the current value is too high the position of the temperature mixing flap will be changed.

- Sun Sensor
The sensor can be found in the middle of the dashboard and is a dual solar sensor. This means that the sun shining in the left and the right side can be measured separately and sent to the control module. The dual sensor has a reference voltage of 5.0 Volt. The measured values have 2 different time constants, so that system chaos does not result, should the sun intensity only change for a moment (for example short tunnels, trees, etc). This means that a reaction only takes place alter this set amount of time goes by. The middle time constant is different for increasing or decreasing sunshine

- Electronic Control Flap AC Compressor (Control Line)

See section "Compressor".

- Relay Circulation Pump (Control Line)

This relay supplies the additional circulation pump with voltage and will be activated for the following functions from the control panel of the Climate Control or over the control module of the DME:
a Function Auxiliary Heat (Control Panel Climate Control; see section "Auxiliary Heat").
b When using residual motor heat. Through this the heater core flow will be guaranteed when the motor is off (control panel Climate Control a wing plan is shown in section "Auxiliary Heat").
c If the heat capacity is too low, the relay is activated through the control panel to increase the heater core flow.
d To cool off the turbos (after motor is turned off) the circulating pump is triggered over the relay (DME control module; see section "Cooling").

When the circulating pump is activated the heating cycle and the cool water cycle can he separated from each other over 3/2 way valves.

- Flap Motor
All flap motors have a feedback potentiometer that provides information about current position. The potentiometer is between a reference voltage of 5.0 Volts and the 0 Volts. This means that between 0 and 5.0 Volts, theoretically, an infinite number of flap positions are possible.
An acknowledgement voltage of 5.0 volts is interpreted as a fully opened flap. The voltage 0 Volt means that the flap is closed. The control module can recognize each end stroke by the increase of the electricity load.

If a new flap motor is installed, it must be calibrated with the PST2 Tester, The new standard positions are saved based on the flap movements.

Unlike previous designs, the flap motor for fresh air/circulating air has a position acknowledgement capability, like all of the other motors. This signal is used for automatic air recirculation operation, because the return to fresh air operation should happen smoothly.

- Fan control (control of air volume)
The air flow in the air distribution housing for the fresh air fan is set by a control module (fan control). The triggering takes place over a PWM signal. The controller changes the fan flow to the desired value and provides the voltage to the low terminal of the fan motor for diagnostic purposes.


Fan Voltage [V] Fan Triggering [%]
0 0
2 16
4 31
6 42
4 55
10 70
12 74
14 100

- AC Flap Supply
This diode is connected to the electronic control flap and functions as a reset device to suppress opposing inductions.

- AUX
This input is not yet used (wiring used later).

- CAN-Bus Comfort HIGH and LOW
The control panel of the Climate Control is connected to the CAN Bus. Over the CAN Bus the control unit receives information and values from the sensors that are not directly wired to the control panel.

What information is provided over the CAN Bus?
- Ignition on (15) (basic pre-requisite for function of the Climate Control)
- Auxiliary heat (operation) on or oft (signal recognized remotely)
- Country versions (realization of country specific fresh/circulating air control) Temperature unit (displayed in degrees C or degrees F)
- External temperature (sensor near the front bumper measures system external temperature)
- Dimming (signal from the instrument cluster)
- Driving speed (correction calculation of the system external temperature at high speeds taking wind into consideration)
- Motor RPMs (decreases RPMS of the vent fan if the motor RPMS change)
- Time (the time is provided by the instrument cluster and displayed in the operating unit)
- Motor temperature (forced suppression of the compressor at critical refrigerant temperatures T > 118 degrees C)
- Off and reduction requests (for example, if the vehicle battery voltage drops, the compressor can be turned off. This can also turn off the rear window heater or reduce the fan standard value.)

What information is provided by the control module of the Climate Control to the CAN Bus?
- Increased RPMs (to stabilize engine speed when AC compressor is in use)
- Rear window heating (impulse to turn on for the control module of the central comfort electrical module in the rear area when the button for rear window heating is pressed)
- Compressor (Calculated compressor load)
- Heat off (status announcement when both front temperature flap are closed)
- Refrigerant pressure (Refrigerant pressure, that is received from the pressure sensor as PWM signal)
- Command for condenser cooling (the cooler vent control is linearly controlled, for Climate Control functions, by the value received by the sensor for refrigerant pressure)
- ECON function (ECON button pressed and compressor off = Zero request)
- Status of the motor residual warmth function