Design
Design
Climate control unit
The climate control unit consists of the following components:
1. Heater element
2. Damper motor, temperature, left
3. Blower fan
4. Damper motor, fresh air / recirculation
5. Power unit for blower fan motor
6. Particle filter
7. Damper motor, ventilation and floor (also defroster for MCC/STD)
8. Damper motor, temperature, right
9. Damper motor defroster (ECC).
Engine coolant constantly flows through the heater element. There is no valve to regulate the flow. The selected temperature is achieved using dampers for the right and left-hand sides of the car installed upstream and downstream of the heater element. These control the amount of air to be warmed. There are also dampers downstream of the heater element that guide the airflow to the correct air vent.
The climate control module provides infinitely variable electronic blower fan control. When AUTO mode (only electronic climate control) is engaged the climate control module (CCM) adapts the blower fan speed to the setting of the controls and the vehicle speed. The blower fan can be set to run-on in order to reduce residual moisture in the evaporator.
A timer located in the central electronic module (CEM) controls the run-on time. 50 minutes after the engine has been switched off and the ignition has been turned to position 0 or I the central electronic module (CEM) supplies power to the climate control module (CCM) and the blower fan is activated at full speed for 7 minutes. This run-on dries the evaporator and prevents bad odors.
This function is programmed at the factory, but can be deactivated in the event of customer complaints via programming of customer parameters. Programming is carried out via VIDA.
The function is only available to cars of structure week 199850 and later.
All damper motors are of the stepper type. Their position and speed is controlled electronically.
Manual climate control and standard climate control have four stepper motors controlling the following dampers:
- Ventilation / floor / defroster via a link system
- Recirculation and fresh air via a link system
- Temperature left
- Temperature right.
For electronic climate control (ECC) there is an extra stepper motor which controls the defroster. The wiring between the damper motors and the climate control module (CCM) consists of four cables for supply voltage and directional control and a separate cable for each motor which controls the motor to be activated. Each motor has four coils. The corresponding coils in each motor are supplied with power at the same time. The motors are only supplied with power if they are grounded at the same time. When a new position is selected for the damper motor, the climate control module (CCM) calculates how many steps are required to complete the movement. The climate control module (CCM) then activates the damper motor with the necessary number of steps. When the motor is instructed to move to an end position, the motor is activated until it stops. This end position is then used as a limit position. This means that the damper motors are self-adjusting, but only after the limit positions have been reached. When replacing the damper motors, ensure that the self-adjustment is carried out. Otherwise the customer may experience defective climate control.
There are diagnostics for the blower fan and damper motors.
Air conditioning (ECC and MCC only)
The engine control module (ECM) controls the A/C compressor. When the A/C switch on the dashboard environment panel is activated, a request to activate the compressor is transmitted via Control area network (CAN) to the engine control module (ECM). The engine control module (ECM) determines when the compressor must operate.
If any of the following conditions are met the compressor is disconnected:
- High engine coolant temperature (ECT)
- Wide open throttle (WOT)
- The engine has just been started
- Overpressure in the air conditioning (A/C) system.
When the engine is started the engine control module (ECM) activates the air conditioning compressor for a short period even if the climate control module (CCM) has not transmitted a request about this. This is carried out for diagnosis. This check is carried out at all temperatures exceeding -6 °C.
The advantage in allowing the engine control module (ECM) to control the air conditioning compressor is that it can delay compressor activation somewhat, if the idling speed must be compensated for the extra load for example.
Sun sensor (electronic climate control only)
The sun sensor transmits information about sun intensity to the climate control module (CCM).
The sun sensor consists of a photo diode which is supplied with power from the control module. The conductivity of the diode depends on the amount of light to which it is exposed. The diode is located under a diffusing lens which reduces the sensitivity of the photo diode to the angle of the light hitting it. Increased sun intensity reduces the voltage over the photo diode. The control module measures the voltage over the photo diode and compensates for high sun intensity by lowering the ventilation air temperature, changing the distribution of air and increasing the speed of the blower fan.
The climate control module (CCM) starts to compensate the blower fan speed at a sun intensity of 400 W/m2and reaches maximum compensation at a sun intensity of 1000 W/m2.
The sun sensor is located in the middle of the dashboard by the windshield.
There are diagnostics for the sun sensor.
Air quality sensor (electronic climate control only, option)
The air quality sensor is available as an option for the electronic climate control from model year 2000. Its function is to transmit a signal to the climate control module (CCM) if it detects increased concentrations of pollutants in the outside air.
The air quality sensor measures the COxand NOxcontent.
The air quality sensor compares current values with previous ones and can calculate changes in pollutant concentrations.
The signal from the air quality sensor to the climate control module (CCM) is a pulse width modulation (PWM) signal and has four stages, 0-3:
- signal 0= no increase in or reduced pollutant level
- signal 1=gradual increase in pollutant level
- signal 2=moderate increase in pollutant level
- signal 3=rapid increase in pollutant level.
The control module uses the signal to control the recirculation damper motor.
The air quality sensor is located on the right-hand side of the fresh air intake under the cowl.
There are diagnostics for the air quality sensor.
Switches, dashboard environment panel, (lower section)
Across the lower section of the dashboard environment panel there is a 12V socket and space for a maximum of seven switches.
Each switch has its own identity. This is unique for the relevant function. The switches can therefore be positioned in any location on the dashboard environment panel, as long as they are installed in the off position. They do not have to be in any particular order. However, the identity of the installed switches must correspond with the car configuration file so that they can be activated.
For further information regarding the car configuration file, see Design and Function, Downloading Software.
There are diagnostics for the switches.
Rear A/C (only XC90 with three rows of seats)
XC90 with three rows of seats is equipped with a rear A/C system. This consists of:
- power unit
- fan
- expansion valve
- blower fan switch.
The rear A/C system is controlled by a switch in the lower section of the dashboard environment panel. When the switch is activated the climate control unit (CCM) transmits a signal to the rear electronic module (REM) via the Control area network (CAN). The rear electronic module (REM) supplies the power unit and the blower fan switch with voltage via a relay. The blower fan switch sends control voltage to the power unit based on the position of the control. The power unit converts the control voltage to supply voltage for the blower fan motor.
The rear A/C is directly connected to the front air conditioning via the high and low pressure pipes and hoses. The only way to control the cooling in the third row of seats is to control the fan speed using the rear fan switch.
The rear electronic module (REM) diagnoses the relay supply, otherwise the rear A/C cannot be diagnosed.