IHKA System Components

IHKA System Components
The IHKA consists of following components:
^ Control panel/control module
^ Heater/air conditioner unit
^ AUC sensor
^ A/C compressor
^ Refrigerant pressure sensor
^ Rear window defogger relay

Note: The solar sensor is not available on the (E85) Z4 IHKA system.





System Overview of IHKA Input/Output Signals

IHKA Control Panel/Control Module





The IHKA control panel/control module is one component and is located in the center of the instrument panel under the radio/navigation control panel (above the center console switch center).





Plug connection, rear of IHKA Control Panel/Control Module
The 3 control elements of the control panel/control unit are enclosed by trim rings. These trim rings are clipped into the instrument panel from the front and can be replaced separately.
The rotary knob for air distribution (adjustment range of 360° rotation) features 3 main settings and 10 precision settings in between.
The rotary knob for blower speed (adjustment range of 180° rotation) features 1 main notch for the zero setting. There are 14 precision settings from the zero position up to the maximum setting.
The rotary knob for temperature setting (adjustment range of 240° rotation) has 2 main settings (maximum cold/maximum warm) with 23 precision settings in between. Temperature setting range:
^ Maximum cold (corresponds to 60°F)
^ Individual temperature setting range (in steps of 1°F)
^ Maximum warm (corresponds to 84°F)
The following buttons feature a green function light (LED): AUTO, A/C, MAX AC. The button for AUC/recirculating air has 2 green function lights (LEDs).
The rear window defogger and defrost buttons feature an orange colored function light (LED). When the vehicle lights are switched on, the indicator lights are activated via terminal 589. The signal comes from the light switch center (LSZ).
The locator lights and function lights are dimmed corresponding to the dimmer control wheel position on the light switch center and/or depending on the ambient light conditions (photocell in light switch center).

Rotating function light
A special feature of the IHKA is the rotary function light in all three knobs. For example; the rotary knob for air distribution has an adjustment range of 360° rotation. 8 LEDs are located on the pc-board (under the knob) at its circumference to ensure it can be seen clearly from different viewing directions.
A light element is located in the rotary knob (connected mechanically) and turns together with it.





The light element functions as a light guide. It bundles the light of the LEDs and, due to its geometrical shape, guides it to the light outlet window of the rotary knob.
This ensures the full light intensity is always emitted at the light outlet window.

Interior Temperature Sensor





A ventilated interior temperature sensor is located in the IHKA control panel. The integrated sensor blower is activated when KL15 is switched "ON". The sensor blower continues to run for 10 minutes after KL15 is switched "OFF".
The after running period is necessary to keep the interior temperature reading fresh.
Otherwise, when the vehicle is parked for a short period of time (e.g. refuelling), due to interior heat build up, the sensor would supply an incorrect value for the interior temperature.
The vehicle interior temperature sensor has a value range from -49°F to 176°F. The evaluation range of the vehicle interior temperature sensor is between 41°F and 122°F. Values below -49°F are stored as a short to B+ or a break. Values above 176°F are stored as a short to B-. The substitute value is 68°F.
The sensor blower is not monitored. In the event of a fault, this will influence the temperature control (regulation). An implausible temperature value may be supplied when the vehicle interior heats up.

IHKA Heater/Air Conditioner





The following components are integrated in the IHKA heater/air conditioner:
^ Actuator, fresh air/recirculating air flap
^ Stepper motor, air distribution, bottom
^ Stepper motor, air distribution, center
^ Stepper motor, air distribution, top
^ Stepper motor, mixed air flap
^ Temperature sensor, mixed air
^ Blower output final stage and blower motor
^ Evaporator temperature sensor

Stepper Motors
The number of steps of the individual stepper motors depends on the adjustment range of the driven flap as follows:
^ Defrost, maximum number of steps 900, fail safe direction flap open
^ Center ventilation, maximum number of steps 1390, fail safe direction flap closed
^ Footwell, maximum number of steps 1600, fail safe direction flap closed
^ Mixed air flap, maximum number of steps 1770, fail safe direction maximum warm
The flaps are moved to their limit stops after KL15 is switched OFF. The stepper motors are not able to detect their actual position. The stepper motors always move relative to a reference point. A flap end position (0% or 100%) serves as this reference point.

Evaporator Temperature Sensor
The evaporator temperature sensor is installed on the heater/air conditioner to measure the temperature of the air flowing out at the evaporator.
The evaporator temperature sensor has a maximum value range from -49°F to 214°F. The evaluation range of the evaporator temperature sensor is between 23°F and 77°F. Values below -49°F are stored as a short to B+ or a break. Values above 214°F are stored as a short to B-. The substitute value is 32°F.

Mixed Air Temperature Sensor





A mixed air temperature sensor is installed on the heater/air conditioner after the mixed air flap to measure the mixed air temperature.
The mixed air temperature sensor has a value range from -40°F to 221°F.
Values below -40°F are stored as a short to B+ or a break.
Values above 221°F are stored as a short to B-. The substitute value is 131°F.

Blower
The radial blower in the Z4 is mounted transversely in the heater/air conditioner. The blower is activated when KL15 is switched "ON", corresponding to the function previously selected (DEFROST, MAX AC, automatic blower function, individual blower setting).
Blower activation takes place in linearly from 0 to 8 Volts. The IHKA is deactivated when the blower is switched "OFF" (zero position). The blower activation is infinitely variable in AUTO mode. The following 5 settings are possible for blower activation:
^ Blower "OFF" (zero position)
^ Individual blower setting
^ Automatic blower (AUTO mode)
^ DEFROST/MAX AC function with automatic blower setting
^ DEFROST/MAX AC function with individual blower setting

AUC Sensor





In automatic recirculating air control (AUC mode), pollutant gasses are detected by the AUC sensor. Based on this input, the IHKA decides whether the system is to assume fresh air mode or recirculating air mode.
The AUC sensor requires a warm up phase of 90 seconds. The AUC sensor is located on the intake shroud of the electric cooling fan (1).

A/C Compressor





The magnetic clutch for the A/C compressor is activated directly by the IHKA control module.
Air conditioning mode is activated by pressing the A/C button. The ECM is signalled to increase the idle speed to compensate for the compressor load. On receiving the A/C compressor ON request from the IHKA control module, the ECM responds with an enable signal on a separate control wire providing no full load cutout request is active. Consequently, the IHKA control module activates the A/C compressor magnetic clutch.
Switching conditions for the A/C compressor magnetic clutch:

A/C Compressor ON
^ A/C button pressed and
^ Evaporator temperature > 2°C (depending on outside temperature) and
^ Outside temperature > - 10°C and
^ System voltage > 9.7 V and
^ Permissible refrigerant pressure range

A/C Compressor OFF
^ Evaporator temperature < -0.5°C (depending on outside temperature) or
^ Blower OFF (zero position) or Outside temperature < -10°C or
^ KL1 5 switched OFF or System voltage < 9 V or
^ Refrigerant pressure out of range (too low/high)
The current Air conditioning ON function is stored in the IHKA when KL15 is switched OFF. Derived from the key memory (personalization), the function last selected is activated when KL15 is switched ON.

Pressure Monitoring
The pressure in the refrigerant circuit is monitored by a pressure sensor. The anticipated A/C compressor load when switching on during operation is derived from the pressure sensor signal.





The load torque in transferred via the K-bus and PT-CAN bus to the ECM. The ECM responds by adapting air and fuel volume. An upper and lower switching threshold is defined for pressure monitoring:





The pressure sensor is fitted in the pressure line near the receiver/dryer. The supply voltage is 5 V and the current is < 20 mA.
Depending on the system pressure, it supplies the IHKA control module with an analog signal between 0.4 V and 4.6 V.

Rear Window Defogger
The rear window defogger has 3 operating statuses. Relay 1 for the rear window defogger is always activated as if a hardtop were installed (no hardtop detection).
Defrost Phase is started only after the first time the rear window defogger button is pressed after KL15 is switched ON (see following table for duration). Relay 2 for the rear window defogger is activated at a rate of 100%. The system then assumes cyclic switching mode.
Cyclic Switching takes place with one third of the total power output of the rear window defogger (pulse/pause ratio = 40 seconds ON/80 seconds OFF). Cyclic switching is deactivated when KL15 is switched OFF.





Restart is possible if the rear window does not remain clear during or after cyclic switching. The full power output can be resumed by pressing the rear window defogger button again. The reheating phase is again followed by cyclic switching.

Rear Window Defogger Undervoltage/Overvoltage Monitoring
To prevent discharge when the vehicle electrical system is subject to high load at low engine speeds (< 1500 rpm), the rear window defogger relays are switched off when the voltage level drops or in the event of overvoltage (> 16 Volt for 5 seconds).
If the system voltage at the IHKA drops below 11.4 Volts, the rear window defogger is switched off and only switched on again when the system voltage exceeds 12.2 Volts. The threshold values must be applied for longer than 10 seconds.
Switching off the relays when undervoltage/overvoltage is detected has no influence on the duration of the operating statuses (defrost phase, cyclic switching, restart) and the function light (LED) remains on while the relays are switched off.
The rear window defogger is also switched off during engine start up (K-bus message, KL50).