Air Conditioning
87 Air conditioning
Functions
The air conditioning controls the interior temperature preselected on the control panel completely automatically. The desired interior temperature can be set between 16.0 °C and 29.5 °C, corresponding to between 61 °F and 85 °F. It is generally recommended to set the interior temperature to approx. 22 °C (72 °F).
The system detects operating and ambient conditions of relevance to the interior climate via sensors and CAN. Automatic control is carried out primarily by means of the interior temperature sensor, the exterior temperature sensor and the solar irradiation energy as detected by a sun sensor. This information is processed in the control unit (control panel) and converted into output signals for temperature control, the air distribution flaps (temperature and air distribution flaps are DC drive motors with position feedback), the fan and the compressor.
In addition to automatic climate control, the control panel also enables manual selection of the desired system status at any time. Changes regarding
- temperature
- air flow rate
- air distribution
can be carried out by means of the control panel.
The cooling output of the air conditioning system is generated by a volume-controlled swash plate (adjustable) compressor. Requirements-dependent metering of the refrigerant delivery capacity helps to save energy, while continuous power consumption of the compressor helps to optimise idle speed.
Controls (control panel of the air conditioning system)
The air conditioning system is operated by means of a control panel (a/c controls) with integrated control unit in the centre console. The control panel differs visually from the previous model because of the addition of a new control interface.
The main changes to the control interface are:
- Integration of the interior temperature sensors (previously in the dashboard on the passenger's side),
- Integration of the switches for heating the driver's and passenger's seats (previously in the centre console).
- Integration of the button for heating the rear window (previously located beside the operating unit).
- Introduction of switches for adjusting the temperature and fan power
(higher setting = switch up, lower setting = switch down).
- "ECO" marking (ECOnomy mode) on the button for switching the air conditioning compressor on and off (snowflake symbol on display goes on/off accordingly).
As a result of these changes, all of the heating functions in the vehicle are now together in a single unit.
Control panel
Information is displayed by means of an LCD display and LEDs in some buttons. When "LO" or "HI" appear on the display of the a/c control unit, this indicates that the system is operating at maximum cooling or heating power (the temperature control function is deactivated). "LO" and "HI" are displayed by the segments employed to indicate the set temperature.
"OFF" on the display indicates that the fan is off.
A - Seat heating on/off
The seat heating settings can be adjusted individually for the left (button A) and right (button G) side. Apart from OFF level, two heating levels can be selected. When the appropriate button is pressed, the air conditioning control unit (control panel) transmits the altered button status (pressed 1x or 2x) to the vehicle electrical system control unit. The vehicle electrical system control unit controls the heating elements in the seat directly (heating-up phase) and reports the relevant heat status (setting 2 or setting 1) back to the control panel. This heating status is indicated to the user via the LED in the seat heating button.
NOTE: Information is provided via CAN for the purpose of dimming the indications on the LCD display.
The operating time during the heating-up phase is based on the interior temperature (CAN signal) according to the selected heat setting:
- Level 2 (at 40 °C to <-20°, or 104 °F to <-4 °F) heats from 2.2 to a maximum of 11.0 minutes
- Level 1 (at 40 °C to <-20°, or 104 °F to <-4 °F) heats from 0.5 to a maximum of 9.2 minutes
NOTE: On the interior temperature (CAN signal) rising above 40 °C or 104 °F, the vehicle electrical system control unit switches off the seat heating. The button status is stored in the vehicle electrical system control unit, thereby activating the seat heating when the temperature drops below 40 °C (104 °F) again.
After the heating-up phase the control unit switches to the continuous heating phase. The vehicle electrical system control unit now reduces the heating power of level 2 to 40 % and level 1 to 14 %.
B - Windscreen
The defrost function can be activated immediately in all operating modes. On activation of this function, the temperature is switched to "HI", the air flow rate is increased and the air is distributed primarily towards the windscreen. ECO mode is additionally ended, if the intake temperature conditions (fresh air intake temperature sensor > 3 °C or > 37.4 °F) permits. If the compressor cannot be activated, recirculation air mode will be started.
C - Recirculation mode
1 - Mode of functioning of manual recirculation mode
The fresh/recirculated air distributor flap can be activated at any time to prevent odour nuisance. However, recirculation mode is limited to max. 3 minutes when the air conditioning compressor is switched off (ECOnomy mode).
2 - Mode of functioning of automatic recirculation mode
At exterior temperatures of > 26 °C or 79 °F, recirculation mode is selected automatically by the program after a ventilation time of 30 seconds in order to accelerate the cooling-down phase - with the air conditioning switched on.
NOTE: The air throughput is influenced by the back pressure which arises in the area of the fresh air inlet according to the vehicle speed. In order to compensate for this dependency, the distributor flap for fresh air/recirculated air (back pressure flap) is moved in the direction of "closed" (recirculated air) according to the vehicle speed (from 90 km/h). The flap setting is also dependent on the fan voltage.
E - ECO button (air-conditioning compressor off/on)
The ECO button enables the selection of ECOnomy mode, which functions without the a/c compressor. ECOnomy mode permits cooling to values below the exterior temperature.
F - Defrost rear windscreen/door mirrors
The heated rear window button in the control panel generates an electrical impulse, which is sent to the vehicle electrical system control unit via CAN. Once the vehicle electrical system control unit has activated the heated rear window relay (in relay holder 2), it sends the switch-on status of the heated rear window back to the air conditioning control panel. The LED in the button on the control panel is then activated.
The ON status of the heated rear window on the CAN bus causes the two door control units (in parallel with the window heating) to directly control the heating elements for the defrost function of the door mirrors.
The maximum heating time for the rear window and door mirrors is 15 minutes.
NOTE: If the outside temperature is > 25 °C or 77 °F (CAN signal), the heating time is just 10 seconds.
I - Automatic mode
Air distribution is controlled automatically. In addition to the state variable "Energy Requirement Level" (see section "Actuators and sensors"), the programme also evaluates the outside temperature and engine temperature in order to take due account of cold start conditions and possible icing of the windows.
Automatic mode is confirmed by the word "AUTO" on the display.
M - Manual fan adjustment
In addition to automatic control, the fan output can also be adjusted manually by means of the rocker switches. The current air flow rate is indicated by a 19-bar indicator on the display.
Pressing the rocker switch up increases the fan output. Pressing the rocker switch down reduces the fan output down to a minimum of zero bars on the display. After releasing the switch and then pressing it down again, the fan is switched off (OFF mode). "OFF" appears on the display. When the fan is switched off, a compressor shutdown function protects the evaporator from icing.
In fan OFF mode, air distribution is set to defrost (defrost/footwell distributor flap) and recirculation (fresh/recirc. air distributor flap) and all other actuators are shut down.
NOTE: The temperature indication on the display of the a/c control panel is switched between °C and °F by means of the on-board computer in the instrument cluster. (This switchover is not adopted by the PCM and must be carried out directly in the PCM if required. See also the section on electrics under "PCM")