Air Conditioning
87 Air Conditioning
Functions
The air conditioning controls the interior temperature preselected on the control panel automatically. The desired interior temperature can be set between 61 °F. (16.0 °C) and 85 °F. (29.5 °C.). It is generally recommended to set the interior temperature to approx. 72 °F. (22 °C).
The system detects operating and ambient conditions of relevance to the interior climate via sensors and CAN. Automatic control is carried out primarily by way 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 way of the control panel.
The cooling output of the air conditioning system is generated by a volume-controlled swash plate (adjustable) compressor. This helps to save energy by controlling the refrigerant flow rate according to the cooling demand and the non-cycling control of the compressor contributes towards optimizing the engine's idling mode.
Operation (air conditioning control panel)
The air conditioning is operated via a control panel (air conditioning controller) with integrated control unit in the center console. The user interface has been revised in comparison to the control panel on the 911 Carrera (996) model.
The main changes to the user 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 center 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 (switch up to increase setting, switch down to reduce setting),
- The button for switching the air conditioning compressor on and off is labelled "ECO" (ECOnomy mode) (snowflake symbol on display goes on and off accordingly).
As a result of these changes, all of the heating functions in the vehicle are now grouped together in a single unit.
Control Panel
The required information is provided via an LCD display and indicator lights (LEDs) incorporated into a number of buttons. When "LO" or "HI" appears on the display of the air conditioning control panel, this indicates that the system is operating at the maximum cooling or heating level (the temperature control function is deactivated). "LO" and "HI" are presented on the display by way of the segments for indicating the set temperature. "OFF" indicates that the fan is off.
A - Seat Heating on/off
NOTE: Information is provided via CAN for dimming the LCD display.
The seat heating levels can be set separately for the seats on the left (button A) and right (button G) sides. The user can choose between OFF and two heating levels for each side. When the appropriate button is pressed, the control unit of the air conditioning system (control panel) transmits the altered button status (pressed 1x or 2 x) via CAN to the vehicle electrical system control unit. The vehicle electrical system control unit activates the heating elements in the respective seats (warm-up phase). and feeds back the appropriate heating status (level 2 or level 1) to the control panel. This heating status is indicated to the user via the LED in the seat heating button.
NOTE: When the interior temperature (CAN signal) of 104° F. (40° C) is exceeded, the vehicle electrical system control unit switches the seat heating off. The button status is saved in the vehicle electrical system control unit so that the seat heating can be reactivated when the temperature falls below 104° F. (40° C).
The ON period during the warm-up phase is determined by the selected heating level and the interior temperature (CAN signal):
- Setting 2 (at 104° F. (40° C) to <-4° F. (-20° C.), heats from between 2.2 to a maximum of 11.0 minutes
- Setting 1 (at 104° F. (40° C) to <-4° F. (-20° C.) heats from between 0.5 to a maximum of 9.2 minutes
After the warm-up phase, the control system switches to continuous heating mode. The vehicle electrical system control unit now reduces the heating output to 40% for setting 2 and to 14% for setting 1.
B - Windshield
The defrost function can be activated immediately in all operating modes and settings. The temperature is then switched to "HI", the air flow rate is increased and the air is distributed primarily to the windshield. ECO mode will additionally be exited, if this is permitted by the intake temperature sensor > 37.4° F. (3° C). If the compressor cannot be activated, the system will switch to recirculation mode.
C - Recirculation Mode
Function of Manual Recirculation Mode
The fresh/recirculated air distributor flap can be activated at any time to prevent unpleasant outside odors from entering the vehicle. However, recirculation mode is limited to max. 3 minutes when the air conditioning compressor is switched off (ECOnomy mode).
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 dependancy, 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 55 mph/90 km/h). The flap setting is also dependent on the fan voltage.
Function of Automatic Recirculation Mode
At exterior temperatures of > 79° F. (26° C), 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.
E - ECON Button (a/c compressor off/on)
The ECO button is used to select ECOnomy mode, which refers to a function without air conditioning compressor. ECOnomy mode permits cooling to values below the exterior temperature.
F - Defrost Rear Window/Door Mirror
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 control panel button is now activated.
NOTE: If the outside temperature is > 77° F. (25° C) (CAN signal), the heating time is just 10 seconds.
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 heated rear window/door mirror heating is 15 minutes.
I - Automatic Mode
Air distribution is controlled automatically. In addition to the state variable "Energy Requirement Level" (see the section "Actuators and sensors"), the exterior temperature and engine temperature are evaluated by the program in order to take account of the conditions associated with a cold start and possible ice formation on the windshield. Automatic mode is confirmed in the display with "AUTO".
M - Manual Fan Override
In addition to automatic control, the fan power can be adjusted manually by moving the switches. The current air flow is indicated by a 19-bar display.
NOTE: The temperature display switchover between °C and °F in the air conditioning control panel display - is performed via the on-board computer in the instrument cluster. (This switchover is not performed by the PCM and must be carried out directly in the PCM if required. See also the section on electrics under "PCM".)
Pushing the switch up increases the fan power. Pushing the switch down reduces the fan power to a maximum air flow of zero bars. After the switch is released and pressed down again, the fan is switched off (OFF mode). "OFF" appears in the display. When the fan is off, a compressor cut-off protects the evaporator against ice formation.
When the fan is in OFF mode, air distribution is set to defrost (defrost/footwell distributor flap) and recirculation (fresh/recirc. air distributor flap) and all other actuators are deactivated.