Functional Description

Functional Description
The Automatic Climate Control System (IHKR) 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 a mixing flap.

The control unit performs open-loop and closed-loop control functions with the aid of a microcomputer:
- Control of fresh air, recirculation air and mixing air flaps.
- Interior temperature control.
- Rear window defogger control.
- Evaporator control.
- Defect detection and diagnosis.
- Use of a substitute value for the failed component.

IHKR Control Panel





1 - Air volume control wheel
2 - Push button for air conditioning system
3 - Temperature control, left side
4 - Temperature control, right side
5 - Push button for air recirculation
6 - Air distribution control wheel
7 - Push button for rear window defogger
8 - Setting for maximum defrosting
9 - Air inlet for interior temperature sensor

Air Distribution Functional Diagram





FK - Fresh air flap (electric).
UK - Air recirculation flap (electric).
SK - 1 mixing flap (electric) for left and right side.
G - Blower
V - Evaporator
KK - A/C compressor
WVF - Water valve, driver's side.
WVB - Water valve, passenger's side.
WTF - Heat exchanger, driver's side.
WTB - Heat exchanger, passenger's side.
K - Radiator
M - 1 mechanical flap with lock between settings air distribution footwell and defrosting for left and right side.
F - Footwell flap (operating cable assembly).
E - Defroster flap (operating cable assembly).
B - Ventilation flap (mechanical in centre grille) = Interior air.

Push Button Controls:
Rear window defogger button:
The rear window defogger is always switched OFF after ignition ON. The rear window defogger can only be activated by means of the push button in the operating unit when the engine is running. The rear window defogger is switched OFF by pressing the push button once again.
Air conditioning button:
The air conditioning button switches ON the air conditioning system.
Air recirculation button:
The air conditioning control and the air recirculation flap program (see flap control) are activated when the air recirculation button is pressed.

Master Controller "Y"
The master controller is a value calculated by the control unit which separately activates the left and right outputs (water valves) dependent on the input values (nominal temperature value, interior temperature and outside temperature). The "Y" value is also used in the calculation of the flap control.
The value of the master controller is between -25% (cooling) and 127 % (high heat requirement).

Air Flap Control
The footwell and defroster flaps are continuously variable by way of the air distribution control wheel (operating cable assembly). The fresh air, air recirculation and mixing flaps are set by means of stepping motors.
The fresh air flaps are controlled dependent on the air flow control wheel and the vehicle speed. The fresh air flap can only be closed up to 20 % during air conditioning mode. If the variable "Y" driver drops below -20% during air conditioning mode, the system is switched over to air recirculation mode. If the variable "Y" driver exceeds -5%, the system reassumes the normal air conditioning mode.
The fresh air flaps are closed to 20 % and the recirculation air flaps open when the recirculation air push button is pressed.
The mixing flap is closed between the settings footwell and defroster of the air flow control wheel (monitored by microswitch). In addition, a mechanical flap with lock facility in this position prevents warm air entering the ventilation duct. Outside this position, the mixing air flap is set depending on the mixing flap control.
After the ignition has been switched OFF, the flaps driven by stepping motors remain in the position last selected.

Air Flap Positions





E - Defroster flap (mechanical).
F - Footwell flap (mechanical).
SK - Mixing flap (electric).
A - Flap open
Z - Flap closed.
SS - Mixing control.
K - Mixing control, position cold.
W - Mixing control, position warm.
S - Operating range of mixing flap.

CONTROL WHEEL AND TEMPERATURE SENSOR FUNCTIONS:

Air Flow Control Wheel
The IHKR control unit takes up operation when the ignition is switched ON. The flap control and air conditioning control are activated when the air flow control wheel is turned out of the zero position. The blower then runs in the first speed stage. The air flow control wheel (potentiometer) only influences the position of the fresh air flap until the first control stage is reached. The air flow is set by turning the air flow control wheel further to stage 4. The blower motor is activated by means of a rotary switch and a resistance circuit. The potentiometer and the rotary switch are coupled to the spindle of the air flow control wheel.

Temperature Control Wheel
The nominal value for the interior 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 these values correspond 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 heating, 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.

Air Conditioning Control
The A/C compressor, the evaporator control and the [1][2]auxiliary fan stage 1 are switched ON when the air conditioning or air recirculation button is pressed.

Evaporator control:
The magnetic clutch of the A/C compressor is disengaged and the [1][2]auxiliary fan stage 1 switched OFF when the evaporator sensor reaches a temperature of <2 °C in order to prevent icing of the evaporator. At an evaporator sensor temperature of >3 °C, the control unit switches the auxiliary fan stage 1 ON again and the magnetic clutch engages.

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.
The activation circuit of the A/C compressor clutch leads from the output of the IHKR control unit to the refrigerant high pressure switch and via the low pressure switch to the DME control unit. The A/C compressor is activated by the DME control unit in conjunction with the A/C relay. When one of the pressure switches cuts out because there is too little or too much pressure in the refrigerant circuit (no or too little refrigerant or too much refrigerant), the A/C compressor clutch disengages in order to prevent the compressor being damaged.

Relay Output
All relays and water valves are switched by applying ground to the corresponding output of the control unit. Diagnosis of the control unit only covers the control circuit of the relays.

Heat Exchanger Control
The water valves are activated dependent on the "Y" value and the engine speed.
The water throughput through the heat exchanger increases as the engine speed increases. To prevent an increase in the heat exchanger temperature, the opening time of the water valves is reduced at a constant "Y" value.
A value of 900 rpm is used at ignition ON and 0 rpm to ensure reliable control of the IHKR in the event of the engine speed signal failing.

Heat exchanger characteristic curve as a function of engine speed





Tv= Opening time of water valve.
1 = Characteristic curve at idle speed.
2 = Characteristic curve at 1900 rpm.
3 = Characteristic curve at 3800 rpm.

Independent Heating / Ventilation
If an independent heating system is installed, the relay box can be activated via the On-Board computer or multifunction clock. This relay box switches the independent heating or independent ventilation program in the IHKR control unit. At a preselected time, the On-Board computer (or multifunction clock) switches ON the independent heating at an outside temperature <16 °C and the independent ventilation at an outside temperature >16 °C.
In independent heating mode (ignition switch position 0) the fresh air flap is open and the air recirculation flap closed. Irrespective of the position of the mixing air control, the mixing flap is positioned to 100 % within the air distribution footwell and defroster and to 82 % outside this setting. The blower runs in speed stage 2 after a water temperature of 55 C has been reached. The water valves are open during operation. The status set at the control unit applies at ignition switch position 1 (terminal R) or ignition switch position 2 (terminal 15).
In independent ventilation mode (only in ignition switch position 0 or 1), the fresh air flap is open and the air recirculation flap closed. irrespective of the mixing air control, the mixing flap is set to 100 % within the air distribution footwell and defroster and to 0 % outside this setting. The blower runs at speed stage 2.

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 30) of the control unit was interrupted or after the ignition was deactivated 10 times. The calibration phase is then started after ignition ON. Error detection differentiates between short to plus, short to minus and a break. If the control unit detects a stepping motor defect, the defective motor is no longer activated. The stepping motors no longer move if the voltage of the vehicle electrical system drops below 9 V or increases above 15 V. The stepping motors operate with only half frequency when the voltage of the vehicle electrical system is between 9 V and 11 V.

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.
The interior sensor blower starts up when the ignition is switched ON. When the ignition is switched OFF, the interior sensor blower remains in operation for a further 3 minutes to avoid a heat buildup in the intake duct of the temperature sensor when the vehicle is stopped for a short space of time.
To ensure effective operation, unobstructed air flow through the ventilation grille in the operating unit must be ensured (no dirt build-up).