Automatic Climate Control (IHKA)
Automatic Climate Control (IHKA):
Functional Description:
The climate control system (IHKA) is a water-based automatic heating and air conditioning system. The control system on the water side is based on two electrically operated water valves in separate heat exchangers on the left and right sides.
The required temperature in the vehicle is controlled by the mixing flaps. The air is mixed ahead of the heat exchangers without being heated in the flow of ventilation air. Temperature control with the mixing flaps is therefore not possible when the ventilation outlet nozzles are closed manually. The control unit performs open-loop and closed-loop functions with the aid of a microcomputer:
- Control of air distribution flaps
- Air flow control
- Interior temperature control
- Cold start interlock
- Rear window defogger control
- Evaporator temperature control
- Auxiliary water pump control
- Defect detection and diagnosis and making available a substitute value for the failed component
All air distribution flaps are set corresponding to the flap program by means of the stepping motors. The left/right Y-value is calculated from the input data (outside temperature, heater temperatures, evaporator temperature, interior temperature, control wheel settings, push button settings etc.) and a corresponding flap program selected.
For safety reasons, the "defrost" flap program is set before the IHKA control unit switches off after approx.. 4 minutes "ignition OFF" (defect code memory is cleared).
Control Wheel and Temperature Sensor Function:
Air Flow Control Wheel:
The IHKA control unit takes up operation when the ignition is switched on. The IHKA can be switched on and the nominal value for the air flow set with the air flow control wheel (exception, defrost program and rear window defogger).
An increase in the set air flow rate by the wind during driving is largely compensated by the fresh air flap closing dependent on the vehicle speed.
The blower is switched off via terminal 50 when starting the vehicle. A switch is coupled with the air flow control wheel to ensure the blower can take up emergency operation in the case of a defect in the air flow control wheel, failure of the control unit or a defect in the output stage electronics. In the maximum position of the air flow control wheel, this switch switches plus to a relay integrated in the output stage, thus bypassing the output stage electronics.
The switch is not included in the diagnostic procedure for the control unit.
Temperature Control Wheels:
The nominal value for the inside temperature is set with the temperature control wheels.
The temperature values printed on the selector wheels of the operating unit do not correspond to the values which are used by the control unit and which can be read out via the status list, but rather to a comfort temperature.
When setting the temperature, the control wheel on the driver's side has priority near the end positions over the control wheel on the passenger's side. When the temperature control wheel on the driver's side is set to maximum, the positive supply to the water valves is interrupted by way of a mechanically coupled switch.
In this position, the control unit interrupts the diagnostic procedure for the water valves which are open when no power is applied.
Relay Outputs:
All relays (also water valves) are switched by applying ground to the corresponding output of the control unit. The diagnostic procedure for the control unit only covers the control circuit of the relays.
Cold Start Interlock:
In order to avoid unpleasant drafts during the warm-up phase (up to 30 °C heater temperature on driver's side and Y left 100 %), the blower is switched to minimum, the air distribution flaps to defrost program and the auxiliary water pump is switched to OFF.
The cold start interlock is reset to ON after ignition OFF ON and heater sensor temperature <30 °C.
Air Conditioning Control:
The NC compressor and the evaporator control are switched on when the air conditioning or circulating air button is pressed. Parallel to this, the [1][2]auxiliary fan stage 1 is also switched on and off at the NC compressor output.
The switching status of the [1][2]auxiliary fan stage 1 can, however, deviate from that of the NC compressor since the magnetic clutch can be disconnected from the DME by means of an opener relay (in the working circuit of the NC compressor relay).
The prerequisite for disengaging the magnetic clutch (for approx.. 7 seconds) is detection of the full load signal at the DME at a speed of <8 km/h.
To avoid a drop in the engine speed, a signal which serves to adapt the idle speed is sent to the DME when the air conditioning system is switched on via the
DME/EML decoupling relay.
To avoid condensation forming on the windows, the evaporator temperature is adapted to the outside temperature after switching off the A/C compressor or after a new start terminal 15.
The control and therefore also the compressor are switched off when the evaporator temperature has reached the value of the outside temperature after approx.. 15 minutes.
Evaporator sensor: The magnetic clutch of the A/C compressor disengages from the A/C relay when the evaporator sensor reaches a temperature of <2 °C.
This prevents the evaporator from icing up. At an evaporator sensor temperature of >3 °C, the control unit switches on the A/C relay once again and the magnetic clutch energizes.
Pressure switch: In order to improve the cooling capacity, the [1][2]auxiliary fan stage 2 is switched on and off depending on the medium pressure switch.
Activation circuit of the A/C compressor clutch goes from the output of the A/C relay (working circuit) to the coolant high pressure switch and via the low pressure switch to the A/C compressor clutch.
When one of the pressure switches cuts out because there is too little or too much pressure in the coolant circuit (no or too little coolant or too much coolant), the A/C compressor clutch disengages in order to prevent the compressor being damaged.
Push buttons:
The push buttons are arranged in 4 blocks.
- Air distribution buttons, driver's side
- Air distribution buttons, passenger's side
- Higher-ranking buttons: Defrost, air conditioning, circulating air or circulating air/AUC
- Rear window button
The air distribution buttons are mutually interlocked by mechanical means. The AUTO button is set by the control unit when no button is pressed.
The defrost program is activated by pressing the defrost button. All current programs are interrupted and the function indicator lights (with the exception of the rear window defogger) of the previously selected program go out.
With the exception of the fresh air and defroster flaps, all flaps are closed and the mixing air flap is set to warm".
The Y-value becomes 100 % (maximum heating capacity) when the outside temperature is >10 °C. The heating is controlled in normal mode (water valves switch in cycles) at an outside temperature >10 °C.
The rear window defogger is additionally switched on automatically when the defrost function is activated for the first time.
The defrost program is switched oft again by pressing the defrost button a second time and the automatic climate control system (IHKA) continues to operate with the previously set program.
With the IHKA switched on and the engine running, the rear window button switches on the rear window defogger when pressed for the first time (defrost stage).
The function lights light up and the defrost time runs for 10 minutes.
After the defrost time has elapsed, the function LED goes out and the rear window defogger is switched oft for 80 seconds and switched on for 40 seconds.
After 20 minutes modulation (cyclic mode), the rear window defogger switches oft automatically. The system is switched to defrost stage if the rear window button is pressed during modulation mode. The rear window defogger is switched oft when the button is pressed once again.
The rear window defogger relay is switched oft if a voltage terminal 15 <11.8 V is detected at the control unit. The relay switches on once again when the voltage exceeds 12.7 V.
In order to maintain the defrost function, voltage monitoring begins 10 minutes alter initial activation of the rear window defogger.
Auxiliary Water Pump:
An electrical auxiliary water pump is installed in order to maintain the necessary hot water throughput at low engine speeds.
The auxiliary water pump is switched on when the outlet temperature on one heat exchanger side has exceeded the value of 30 °C after a new start and the control variable YL OR YR is above 30 %.
The auxiliary water pump is switched oft when the control variables YL AND YR drop below the value of 25 %.
Independent heating / Independent ventilation:
If an independent heating or independent ventilation system is installed, the switch-on time can be entered via the multi/informtion display (MID). The EKM activates the relays which switch the independent heating or independent ventilation program in the IHKA control unit. At the selected time, the EKM switches on the independent heating at an out- side temperature <16 °C and the independent ventilation at an outside temperature >16 °C.
Stepping motors:
Stepping motors are installed in order to move the various flaps. The control unit assumes that, after completing the calibration phase, the stepping motors are in a defined position since the stepping motors cannot signal back their position to the control unit.
The calibration phase is triggered when the power supply (terminal 15 and terminal 30) of the control unit was interrupted. The calibration phase is then started after ignition ON.
The corresponding motor is switched off if the control unit detects a stepping motor defect.
It resumes operation when the ignition was switched off for >4 minutes or a calibration run is triggered and the motor is found to be okay.
The stepping motors have an adjustment time of approx.. 12 - 16 seconds. An exception to this is the fresh air motor which has an opening time of approx.. 12 seconds and a closing time of approx.. 2 seconds.
Interior Sensor Blower:
The interior sensor blower ventilates the interior sensor. This ventilation prevents overheating of the interior sensor and the control unit operates with the current interior temperature value.
To ensure effective operation, unobstructed air flow through the ventilation grille in the component must be ensured (no dirt build-up).