Part 2
Temperature control
In the heating/air-conditioning system, the air-mass flow is first cooled and dried at the evaporator (provided the air conditioner is switched on). Then the airflow is heated to the required temperature at the heating system heat exchanger.
- IHKA Basic
The temperature in the heating system heat exchanger is controlled with the help of the heating system heat exchanger sensor and a pulsed water valve in the heater circuit. The water valve is actuated with a pulse-modulated signal (PWM signal) by the IHKA control unit. A map for the heating system heat exchanger determines the opening times for the water valve, depending on the engine speed.
A master controller regulates the temperature inside the vehicle. Regulation is based on the specification set at the rotary switch (adjustment range: 17 - 27° C) and the actual value (= interior temperature).
The lead parameter is derived from the comparison of the actual interior temperature and the corrected specification (customer setting + ambient temperature). Compared to the set specification, the interior temperature is raised in the cold so that a comfortable level is achieved even at negative temperatures, despite the temperature setting being unchanged. The ambient temperature is transmitted through the body CAN (controller area network) to the IHKA control unit.
An auxiliary regulating circuit relieves the master controller by eliminating any fault quantities that could be detected in the heating/air-conditioning system in the form of a temperature change. Disturbances are caused by:
- Fluctuations in air volume
- Fluctuations in coolant flow in engine heater circuit
- Temperature changes in fresh air
- IHKA High
The separate temperature setting for the drivers side and the front-passenger side affects:
- heating system heat exchanger with left/right separation
- 2 heating system heat exchanger sensors
- Dual water valve
The temperature is regulated by 2 master controllers. Regulation is based on the specification set at the rotary switch and the actual value (= interior temperature).
Through the left/right separation, 2 auxiliary regulating circuits relieve the two master controllers.
The solar sensor compensates for additional fault quantities caused by external sources of light or heat (e.g. direct sunlight).
Note: Reaching maximum outlet temperature in ventilation area.
The maximum outlet temperature in the ventilation area is reached as follows:
- Set the rotary switch for temperature selection to maximum temperature (28° C)
- Set temperature layering as follows with the CID:
- IHKA Basic:
air stratification to "red" (warmer)
- IHKA High:
All 4 red bars must be displayed.
Evaporator control
The evaporator temperature is regulated with the help of the evaporator temperature sensor and a controllable expansion valve. The evaporator temperature is set to the predefined specification of 2 °C. Lower temperatures are not possible due to the risk of icing.
If the "variable evaporator control" function has been encoded, the nominal evaporator temperature is calculated between 2 and 7° C. The specification depends on the ambient temperature, the ventilation temperature and the refrigerant pressure. A variable evaporator control reduces dehumidification. This reduces the risk of mucous membranes drying out.
Air distribution setting
Occupants have the possibility of allowing the air distribution to be decided by the automatic program (AUTO button). Alternatively, manual selection (defrost, ventilation, footwell) allows an individual, personal air distribution.
Important for the optimal function of the air distribution is that the manually adjustable air vents are open.
Airflow control
The airflow control is dependent on the following settings and control actions:
- Manual blower setting
The blower setting is made with the rotary switch in the IHKA controls.
- Automatic blower and flap setting
The automatic blower and flap functions are activated when the AUTO button is pressed.
- Automatic blower speed increase
The automatic blower speed increase function is available with both manual and automatic flap settings.
To make a rapid heating or cooling possible from extreme interior temperatures, the standard range of adjustment is extended.
- Dynamic pressure compensation
Without dynamic pressure compensation, the airflow through the fresh air grille would be increased disproportionately with increasing road speed. This effect is compensated for by the opening angle of the fresh-air flap being reduced as speed increases. (The road speed comes from the instrument cluster, through the body CAN to the IHKA control unit The opening angle is regulated according to an empirically defined map.)
- Blower control
If needed, priority levels are transmitted (through the body CAN) from the power module consumer cutoff to reduce the blower output.
- Effect of terminal 50
During the starting process (terminal 50 ON), the blower is set to OFF to relieve the vehicle battery.
Sunlight adaptation (solar sensor, IHKA High only)
The influence on IHKA regulation by the solar sensor is assigned separately to the driver's side and to the front-passenger side.
The following functions are modified when automatic mode is activated:
- Blower (individual blower proportions of the overall blower output are increased or decreased)
- Air stratification (stratification temperature adjusted)
- Flaps (position of ventilating flaps adjusted)
MAX cooling (IHKA High)
The MAX button makes it possible for the user to select maximum cooling with just one press of a button at the IHKA controls.
When the MAX button is pressed, all functions, including the defrost function, are deactivated. The air-conditioning function is activated (if it was not already activated) and defined settings are selected (e.g. temperature control is deactivated, the dual water valve is closed).
Maximum heating
If the rotary switch for temperature selection is turned to the end stop, maximum heating is activated. Regulation of the interior temperature is suspended. Predefined settings are selected (e.g. temperature of heating system heat exchanger regulated to maximum setting 90° C).
Residual heat (IHKA High only)
The residual-heat function makes it possible to utilize the waste heat from the engine to heat the vehicle interior when the engine is not running. The additional coolant pump is activated to circulate the water.
Switch-on conditions:
- REST button in IHKA controls ON
and
- Ambient temperature below 25° C
and
- engine temperature above 60° C
and
- ignition lock position R or ignition OFF
and
- 15 minutes after terminal 15 OFF not yet expired
Defrost function (IHKA High only)
The defrost function is activated with the defrost button in the IHKA controls. This opens the defroster flap (on the inside in front of the windscreen) fully. The fresh-air/air-recirculation flaps move to the "fresh air" position. All other flaps are closed. The blower can be set manually.
Heated rear window
The heated rear window is switched on by pressing the heated rear window button in the IHKA controls. The function indicator lamp in the button lights up.
The heated rear window is switched off when the button is pressed again, or automatically when the heating period of 10 or 17 minutes has expired. If the button is pressed again during the heating phase, the after-heating phase (approx. 5 minutes) starts.
- Defrosting phase
When terminal 15 is switched ON, the first time the system is switched on, the time span for the heated rear window is defined as follows:
Ambient temperature down to -15° C: heating period: 10 minutes
Ambient temperature below 15° C: heating period: 17 minutes
- Pulsing
After the defrosting phase, the heating phase (60 minutes at 1/3 heat output pulsing) begins (on-off cycle: 3 seconds ON, 9 seconds OFF).
The function indicator lamp in the button is off during pulsing.
Heated washer jets
The washer jets are heated, depending on the ambient temperature (under 3° C). The IHKA control unit actuates the nozzle heating.
OFF
Press the OFF button to completely switch the IHKA controls off.
Air-recirculation mode
In recirculated-air mode, the flow of outside air can be stopped to prevent pollution from entering the vehicle, e.g. in traffic congestion. Air from the vehicle interior is continuously circulated.
To prevent the windows from misting over, air recirculation is only available for a limited period of time.
Automatic air recirculation
In automatic mode, the system will automatically switch to air-recirculation mode if an extreme cooling output is called for. This allows the vehicle interior to be cooled more quickly. Air from the vehicle interior that has already been cooled is fed through the evaporator again. This reduces the temperature level much faster than it would in normal operation.
Automatic air-recirculation mode initially runs for 12 minutes in full air-recirculation mode and then continuously in partially fresh-air mode (fresh-air flap opening angle: approx. 10%).
Automatic air-recirculation control (IHKA High)
If the AUC sensor detects an excessively high level of emissions in the environment, the IHKA control unit will automatically switch to air-recirculation mode.
Because of the lack of a fresh-air supply, air-recirculation mode is only available for a limited period of time:
- In heating mode at ambient temperatures above 6° C, air recirculation is limited to 4 minutes. This is followed by fresh air for 1 minute.
- In air-conditioning mode at ambient temperatures above 6° C, air recirculation is limited to 12 minutes.
This is followed by fresh air for 1 minute.
- At ambient temperatures between 6° C and 0° C, air recirculation is limited to 3 minutes.
At ambient temperatures below 0° C, air recirculation is limited to 2 minutes.
This is followed by fresh air for 1 minute.
When the engine is started and the AUC function activated, fresh air is always selected for approx. 40 seconds due to the warming phase of the AUC sensor.
Program for avoiding condensation on the window surfaces (IHKA High only)
Measures to prevent condensation on the windscreen depend on a number of conditions:
- Engine running
- The IHKA must be in automatic mode
The IHKA control unit evaluates condensation sensor signal (humidity). If condensation on the windscreen is imminent, the following measures are initiated in turn until the condensation has been eliminated. If a measure proves to be ineffective, the next measure is initiated. Once successful, the measures previously performed are reversed step-by-step in reverse order.
Measures against condensation on windscreen:
- Open the defrost flaps further (max. 17.5%)
- Switch to partially fresh air from air-recirculation/AUC/automatic air-recirculation mode
- Switch from partially fresh air in air-recirculation/AUC/automatic air-recirculation mode to fresh air
- Switch off variable evaporator control
- Raise blower speed (max. 28%)
- Reduce airflow to footwell (by about 60%)
- Increase temperature setting (by max. 2.5° C)
Convertible program (E64 only)
The convertible program is activated in the factory. (this factory setting can be deactivated win the Car and Key Memory)
Switch-on conditions:
- Terminal 15 ON
- Convertible top open
The convertible program comprises the following functions:
- The condensation sensor is switched off
- The blower speed increases with increasing road speed
- Air distribution is switched to the upper body and head, airflow to the footwell is throttled
- Dynamic pressure compensation is changed, i.e. as road speed increases, the volume of air fed into the vehicle through the fresh air grille increases.
- Solar sensor control variables are changed
When the convertible top is open, the solar sensor evaluates the surrounding brightness (darkness to intense sunshine) more strongly. For this reason, the solar sensor has a stronger effect on the IHKA controls when the convertible top is open.
In the convertible program, the blower speed can be changed manually at the IHKA controls. The automatic flap control remains active (no change to flap position).
If the convertible program is active and the flap positions are changed with the CID and controller, the convertible program will be deactivated. This means that manual settings will be assumed, unchanged settings will revert to those that the air-conditioning system had before the convertible top was closed.
The convertible program can be completely reactivated by pressing the AUTO button.
Independent ventilation function
The independent ventilation function is activated either via the Central Information Display (CID) or via Telestart (through the Car Access System (CAS)). There are 2 ways of activating the system via the CID:
Direct operation or programming using the timer.
If the independent ventilation function is programmed via the timer, the independent ventilation function will only be available at exterior temperatures above 15° C.
The battery charge level is constantly monitored by the intelligent battery sensor throughout the independent ventilation function. If the necessary charge level is not maintained, the IHKA control unit will deactivate the independent ventilation function.
Independent heater (option 536)
The independent heating function is activated either via the Central Information Display (CID) or via Telestart (through the Car Access System (CAS)). There are 2 ways of switching the system on via the CID:
Direct operation or programming using the timer.
Conditions required for switching the independent heater on:
- Exterior temperature below 15° C (only applicable after programming with the timer)
- Sufficient fuel in the vehicles tank for a range of at least 50 km
- On-board supply voltage OK
The independent heater has the following functions:
- Auxiliary heating with running engine (pseudo auxiliary heating)
- Telestart (via CAS)
- Low-voltage cutout
Auxiliary heating with running engine (pseudo auxiliary heating)
When the independent heating is running, pseudo auxiliary heating mode is started when the engine is started. During pseudo auxiliary heating mode, the indicator lamp for the independent heating is off.
If the engine temperature is greater than or equal to the temperature of the independent heating circuit, the system will change from pseudo auxiliary heating mode to auxiliary heating. These two modes differ in that only the independent heater circuit is used in pseudo auxiliary heating mode, while in auxiliary heating mode the larger heater circuit is used.
Telestart (via CAS)
The average range of the Telestart transmitter is approx. 150 meters. The CAS forwards the signal from the Telestart transmitter through the body CAN to the following control units:
- IHKA control unit
- Independent heater control unit
Low-voltage cutout (via DME/DDE)
The battery's charge level is constantly monitored by the intelligent battery sensor throughout the independent heating operation. If the necessary charge level is not maintained, the IHKA control unit will deactivate the independent heating operation.
Notes for service staff
Service staff should note the following points:
- General information:
- Diagnosis: ---
- Encoding/programming:
- Car and Key Memory:
National versions
The hardware of the IHKA controls are available temperature displays in ° C (Celsius) or in ° F (Fahrenheit).
Subject to change.