Integrated Automatic Heating / Air Conditioning System (IHKA)
Integrated Automatic Heating / Air Conditioning System (IHKA)
Integrated automatic heating / air conditioning system (IHKA)
In this function description, the following heating and air conditioning systems are described:
- Basic integrated automatic heating / air conditioning system
- High integrated automatic heating / air conditioning system
The integrated automatic heating / air conditioning system is a heating and air conditioning system that is controlled at the air side.
Differences between the heating/air conditioning systems:
Brief component description
The following components are described for the heating and air conditioning system:
- IHKA control unit with integrated control panel
- Blower with blower output stage
- Electric auxiliary heater
- Flap motors
- Stratification control wheel
- Sensors
- Interior-temperature sensor
- Refrigerant pressure sensor
- Evaporator temperature sensor
- Rain-light-solar-condensation sensor
- Sensor for automatic air recirculation mode
- Footwell temperature sensor
- Ventilation temperature sensor
- Air conditioning compressor
- Condenser with integrated dryer flask
- Expansion valve
IHKA control unit with integrated control panel
The control panel and control unit of the integrated automatic heating / air-conditioning system (IHKA) have been combined to form one component.
Basic integrated automatic heating / air conditioning system
The basic integrated automatic heating / air conditioning system has no display for showing the selected temperature setting and the blower speed. There is only a shared facility for adjusting the temperature setting for the driver side and the front passenger side.
The basic integrated automatic heating / air conditioning system has no AUC function.
The air distribution flap motor drives the central kinematics with cam disc. The central kinematics are used to mechanically adjust the air distribution flaps. The microswitch records the current position of the cam disc and thus the position of the air distribution flap motor.
The basic integrated automatic heating / air conditioning system is operated using the operating elements shown in the illustration. The control unit regulates the climate control to the desired temperature. In doing so, the control unit picks up the sensor signals and continuously adapts the adjusting values for blow-out temperature and blower output. The seat heating (if fitted) is also operated using buttons in the operating unit.
IHKA-High
The IHKA High has separate temperature settings for the driver's side and the front passenger side.
The IHKA-High has no display for showing the selected temperature setting and the blower speed.
The IHKA-High is operated using the operating elements shown in the illustration. The nominal temperature is set on the control panel separately for the driver's and front passenger's side. The control unit regulates the climate control to the desired temperature. In doing so, the control unit picks up the sensor signals and continuously adapts the adjusting values for blow-out temperature and blower output. The seat heating (if fitted) is also operated using buttons in the operating unit.
Blower with blower output stage
The blower consists of the blower motor, the fan wheel, the blower output stage and the housing.
The blower creates the necessary air-mass flow in the heating and air conditioning system. The IHKA control unit specifies the blower output stage of the nominal voltage for the blower motor. The nominal voltage is output by the IHKA control unit via a pulse-width modulated signal. The activation of the blower motor via the blower output stage takes place depending on this control signal.
Electric auxiliary heater (only vehicles with diesel engine)
The electric auxiliary heater works on the principle of PTC (positive temperature coefficient) and is installed in the heating and air-conditioning unit. The electric auxiliary heater directly heats up the air to adjust the temperature of the passenger compartment.
Operating principle
The following functions are explained:
- Heating element
- Activation of the electrical auxiliary heater
Heating element
The heating elements in the electric auxiliary heater are PTC resistors. The heating elements are made up of individual ceramic semiconductor resistors. A number of heating elements form a heating section.
The resistance of the heating element has a positive temperature coefficient as of a certain temperature TRmin, In other words, as the temperature rises, the electrical resistance of the heating element also increases. This limits the maximum power consumption. In the operating range, the heating elements have an almost linear curve. These electrical characteristics of the resistors enable a temperature of approx. 120 °C in the area surrounding the heating elements that presents no problem for the heater/air conditioning system.
This "physical" overheat protection is ensured, even in the event of a blower failure.
The temperature of the heating element rises rapidly when current is applied. The heating elements can reach a maximum temperature of approx. 180 °C. From about 8 0 °C , the heating element begins to throttle its current consumption down. The heat from the heating element is fed into the heating chain. The air-mass flow generated by the blower floes passed the heating section. This warms up the air-mass flow. The warm air is then fed into the vehicle interior.
Activation of the electrical auxiliary heater
The electric auxiliary heater is activated by the IHKA control unit via the LIN bus.
The PWM signal from the DDE (digital diesel electronics) informs the electronic circuitry in the electric auxiliary heater of the maximum amount of electrical power available (depending on resources in the vehicle electrical system).
The electric auxiliary heater receives its power supply from the front power distribution box.
Flap motors
The flap motors are actuated by the IHKA control unit via the LIN bus and are supplied with power and an earth connection. In the rest state, the control unit switches the power supply off.
The flap motor is fitted with an integrated circuit. This circuit controls the coil of the flap motor. The circuit has bus- and diagnosis capabilities. After activation of the flap motor, the integrated circuit sends position feedback (actual position) to the control unit. The flap motors communicate across the LIN bus with the HKA control unit. The flap motors are switched in series on the LIN bus. Each flap motor is assigned a certain address. The address determines which function the flap motor assumes in the system network. For example, the footwell flap motor knows that messages are being addressed to it via this address (e.g. open flap). This address tells e.g. the IHKA control unit which flap motor has sent it a fault message.
The following flap motors are installed in IHKA-Basic :
- Air distribution flap motor
- Fresh air/recirculated air flap motor
- Mixing flap motor
Actuation of central kinematics via the air distribution flap motor (IHKA-Basic only)
The air distribution flap motor has the task of setting the air distribution over a cam disc. The air distribution flap motor has no way of recognizing the actual position. To allow the cam disc to be unambiguously positioned despite this, there are two cams of different widths on the cam disc. The micro-switch signals to the IHKA control unit that the cams have been passed over. This mechanism achieves reliable and rapid positioning of the cam disk.
The following flap motors are installed in IHKA-High :
- Defroster flap motor
- Fresh air/recirculated air flap motor
- Mixing flap motor, left
- Mixing flap motor, right
- Ventilation flap motor
- Footwell flap motor
- Stratification flap motor
- Rear-compartment stratification flap motor
Stratification control wheel
The selected potentiometer setting is implemented on the flap position of each flap motor.
Sensors
The following sensors are installed in the heating and air conditioning system:
- Interior-temperature sensor
An interior temperature sensor (not with forced ventilation) is installed in the IHKA controls.
The interior temperature sensor measures the air temperature in the vehicle interior.
- Refrigerant pressure sensor
The refrigerant pressure sensor is located in the pressure line between the condenser and the evaporator. Depending on the sensor signal, the air-conditioning compressor is regulated by the IHKA control unit in the event of excessive refrigerant pressure.
The junction box electronics supply the refrigerant pressure sensor with voltage. The data are evaluated in the junction box electronics (JBE). The prepared data is sent across the body CAN (K-CAN) to the IHKA control unit.
- Evaporator temperature sensor
The evaporator temperature sensor picks up the outlet temperature of the cooled air at the evaporator to prevent freezing of the evaporator.
The evaporator temperature sensor is directly connected to the IHKA control unit.
- rain, light and precipitation solar sensor (IHKA-High only)
The solar sensor and condensation sensor are parts of the rain light solar condensation sensor. The solar sensor enables the integrated automatic heating and air conditioning system (IHKA) to take account of solar radiation. The solar sensor measures the sunlight on the vehicle. The sunlight on the driver's side and front passenger side are detected separately.
The condensation sensor enables the IHKA to detect window condensation at an early stage, even before the driver can detect it. Counter-measures (program for the prevention of condensation) can be taken in good time without the need for driver intervention.
The condensation sensor provides the following information:
- Temperature on inside of the windscreen
- Air humidity on inside of the windscreen
The sensor data is processed in the evaluation electronics unit of the rain, light and precipitation solar sensor. The rain light solar condensation sensor provides the data via the LIN bus. The junction box electronics (JBE) adopts the signals into the corresponding CAN message and sends them. The IHKA control unit is equipment attached to the bus on the K CAN. If the rain and/or condensation sensor system fails, a fault entry is made in the junction box electronics (JBE).
- Sensor for automatic air recirculation mode
The AUC sensor is a metal oxide sensor. This sensor is highly sensitive to various smells and pollutants that are typical of traffic.
The AUC sensor evaluates the concentration of carbon monoxide and nitrogen oxides in the intake fresh air. The AUC sensor converts the detected air quality (also referred as air grade) into an electrical signal. To simplify processing of the information, the air quality in divided into 10 grades:
- Grade 0 to 10 (clean to severely contaminated)
The AUC sensor transmits the corresponding grade as a digital signal via the LIN bus to the junction box electronics (JBE). The junction box electronics transmit the digital signal via the CAN bus to the IHKA control unit. If the automatic air recirculation control sensor measures an emission value that is too high, an automatic changeover recirculated air operation takes place via the IHKA control unit.
- Ventilation temperature sensor
A sensor is integrated into the heating and air-conditioning unit to measure the ventilation temperature. The ventilation temperature sensor measures the delivery temperature directly at the centre ventilating flap on the driver's side. The ventilation temperature sensor is directly connected to the IHKA control unit
- Footwell temperature sensor
A sensor is integrated into the heating and air-conditioning unit to measure the footwell temperature. The footwell temperature sensor measures the blow-out temperature directly at the footwell flap on the driver's side. The footwell temperature sensor is directly connected to the IHKA control unit.
Air conditioning compressor
The air-conditioning compressor compresses the refrigerant taken in by the evaporator. The refrigerant is pressed towards the condenser.
The air-conditioning compressor driven by the engine by means of a belt drive. The air-conditioning compressor is switched on and off via a magnetic clutch.
Stepless power control is possible in the air-conditioning compressor. Within the A/C compressor, the delivery volume and thus the pressure in the refrigerant circuit is generated by pistons. The piston stroke is controlled by a swash plate. The electric control valve on the A/C compressor influences the balance of forces on the swash plate and thus the adjustment of the displacement.
The junction box electronics (JBE) control the control valve with a clocked voltage. The IHKA control unit prompts the actuation. For the purpose of load reduction, only the cooling power that is directly needed is generated.
Condenser with integrated dryer flask
In the condenser, gaseous refrigerant is converted into liquid refrigerant. In the integrated downstream drier flask, any water present in the refrigerant circuit is bound.
Expansion valve
The expansion valve controls the injection quantity into the evaporator. Only as much liquid refrigerant enters the evaporator as the evaporator is able to completely evaporate. Drops of liquid that have not been evaporated would cause damage in the A/C compressor.
System functions
The following system functions are described:
Functional networking
In the following graphic, the functional networking for the integrated automatic heating / air conditioning system is displayed.
Notes for Service department
General notes
Running in the air-conditioning compressor
After replacement of an air-conditioning compressor or refilling the refrigerant circuit, the air-conditioning compressor must be run in. Running in is required to ensure lubrication (oil distribution). Running in can only be carried out using the BMW diagnosis system.
This running in can only be carried out with the air conditioning compressor at idle speed. Here, the oil volume filled by the manufacturer mixes evenly with the liquid refrigerant. If the engine speed exceeds the specified engine speed range, running in is aborted automatically. The running-in procedure must then be repeated in its entirety.
Encoding the rain, light and precipitation solar sensor
Encoding of the rain, light and precipitation solar sensor is required after replacement of the windscreen or replacement of a rain, light and precipitation solar sensor.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.