Climate Control Inputs BMW 7 series E38 facelift

POWER AND GROUND INPUTS

Constant battery power supply (KL30) is necessary for IHKA operation as well as memory (early systems).

Switched ignition power (KL15) is required for IHKA operation when the ignition is in the "run" position. This allows the system to operate after the vehicle has been started (or limited IHKA operation if the engine is not running).

Grounds KL 31

Ground paths are provided to the IHKA to complete the circuits of the inputs, processing, and output control functions.

Scheme 336

STARTING INPUT

The starting (cranking KL50) input is monitored by the IHKA to "unload" consumers during engine cranking. This is a momentary signal that will cause the IHKA to deactivate heavy power consumers.

This signal has a dedicated circuit on E31/36 models, and is transmitted via BUS communication on all other models.

Scheme 337

DISTRIBUTION/AIR DELIVERY SELECTION

Distribution/air delivery selections are made at the control panel. On E31 models, the requested selection is monitored by the control module which is remotely mounted. On all other models, the requested input selection is internally monitored because the control panel and control module are a combined unit.

The E31 control panel is provided as an example. The IHKA control module provides the power supply for the control panel, then monitors the return voltage to determine the distribution/air delivery selection. Notice that the "AUTO" selection only illuminates the LED. The input is not monitored, therefore if no other selection is taken the system is in the auto program.

Scheme 338

TEMPERATURE SELECTION

Temperature selections are made via thumbwheels (early systems), and rocker switches (later systems). On E31 models, the requested temperature selection is monitored by the control module which is remotely mounted. On all other models, the requested input selection for temperature is internally monitored because the control panel and control module are a combined unit.

The E31 control panel is provided as an example. The IHKA control module provides the power and ground supply for the control panel potentiometers, then monitors the return voltage from the potentiometers to determine the temperature selection.

Scheme 339

BLOWER CONTROL

Blower control operation is in operation with the ignition switched on (KL15). The blower speed is controlled by regulating (varying) the ground circuit through the use of transistors (final stage unit).

The IHKA control module determines the appropriate blower speed using these primary inputs

1. Blower control thumbwheel/rocker switch inputs
2. The "Y-factor"

The On E31 models, the requested blower speed selection is monitored by the control module which is remotely mounted. On all other models, the requested input selection for blower speed is internally monitored because the control panel and control module are a combined unit.

The E31 control panel is provided as an example. The IHKA control module provides the power and ground supply for the potentiometer, then monitors the return voltage to determine the blower speed selection.

Scheme 340

STRATIFIED AIR

The request for air temperature stratification is made by a thumbwheel located in the front center face vent outlet and the rear passenger console outlet (if equipped). The thumbwheel potentiometer receives power and ground from the IHKA control module which also monitors the variable return voltage. In addition, the rear console outlet contains a micro-switch (on/off request) that signals to the IHKA control module to allow air flow to the rear console.

Scheme 341

TEMPERATURE SENSOR MONITORING

Several different temperature sensors provide inputs to the IHKA control module. As previously covered, they are the NTC type. The IHKA control module provides the power and ground paths. The module also monitors the circuit voltage variation to determine temperatures. This test applies to the following sensors

Scheme 342

1. Interior (internal control module circuit for all models except E31)
2. Ambient (dedicated for E31/36, all other models supplied from Instrument cluster via K-bus)
3. Heater core
4. Evaporator

AUTOMATIC RECIRCULATED AIR (AUC if equipped)

The IHKA control module uses data from the AUC sensor to determine whether recirculating air mode is necessary. The AUC sensor samples ambient air that has entered the engine compartment. The sensor contains a gas sensor, which measures the level of oxidizable gasses in the air. These include hydrocarbons, NOx, SOx, and CO.

The IHKA control module monitors the change in the voltage signal as these gasses influence the sensor. The second circuit shown is a heating circuit which enhances the sensor's reaction time. When starting the vehicle, fresh air is always supplied for 90 seconds due to the AUC sensor heat-up time.

Scheme 343

COMPRESSOR SHUT OFF SIGNAL (if applicable)

The IHKA module monitors the full load input from the ECM. If the ECM detects "full load" conditions, it signals (KOREL) the IHKA control module to disengage the A/C compressor. The conditions for full load are

Scheme 344

1. Vehicle speed less than 10 mph, and
2. Throttle is wide open or
3. Engine coolant temperature is too high The compressor is turned off for a maximum of 4 minutes (actual duration differs per system).

REFRIGERANT PRESSURE SENSOR (if applicable)

The IHKA control module supplies the power and ground paths, as well as monitoring the variable voltage signal from the refrigerant pressure sensor (located in the receiver/dryer). Based on the refrigerant pressure, the IHKA module "anticipates" the start up torque of the A/C compressor. If the pressure is too low or high the compressor will be deactivated.

This input is also used to vary the auxiliary fan speed and transfers this information on to the ECM via the K-bus.

Scheme 345

WATER VALVES

Temperature regulation on IHKA systems is accomplished by solenoid actuated water valve(s). The valve(s) are normally held open by spring pressure (failsafe), and are electrically closed by pulses from the IHKA control module to regulate the flow of hot coolant to the heater core(s).

The water valve(s) are pulsed according to the Y-factor, which is calculated from the following inputs

1. Desired temperature request (left and right if equipped)
2. Interior temperature
3. Heater core temperature(s)
4. Ambient air temperature
5. Blower speed request

When the desired temperature calls for maximum heat, the water valve(s) do not receive pulses and are mechanically sprung open.

Similarly, when maximum cooling is requested, the IHKA control module powers the water valve(s) completely closed.

Scheme 346

AUXILIARY COOLANT PUMP

All models except E36/46 use an electrically powered auxiliary coolant pump to ensure that an adequate supply of hot coolant is always available to the heater core(s). The IHKA control module operates the pump directly (E31 uses a relay) by supplying the ground circuit.

Pump "ON" operating criteria (E38 shown as an example)

1. Engine coolant temperature > 32°F (supplied via K-Bus on E38/39/46)
2. Y-factor > 5%
3. Maximum defrost mode selected
4. Maximum heating requested
5. "REST" function requested

Pump "OFF" when

Scheme 347

1. Engine coolant temperature < 32°F and either Y-Factor < 0%, unless other inputs call for pump operation

BLOWER SPEED SIGNAL

The blower speed is controlled by the IHKA control module regulating (varying) the ground circuit through the use of transistors (final stage unit).

The IHKA control module determines the appropriate blower speed using these primary inputs

1. Blower control thumbwheel/rocker switch inputs
2. The "Y-factor"

In the case of the E38 (shown), each of the blower speed requests are monitored by the IHKA control module. The control module always runs the blower at the higher selected speed to ensure adequate air flow through the interior. The outlet flap opening will be reduced on the side requesting less blower speed.

Note. Some models do not use a blower relay.

Scheme 348

STEPPER MOTOR CONTROL

Stepper motors are installed in the system to provide infinitely variable operation of the air outlet flaps for automatic climate control. M-Bus (3 wire flat harness) controlled motors are used to operate all flaps, with the exception on some models of a dedicated fresh air motor and circuit.

Each of these motors features its own electronic circuitry and is electrically coded, indicating that installation is unique to a specific flap.

These type of stepper motors receive power and ground on two of the terminals, and coded operating instructions on the third. The instructions are digital signals (500 Hz) that control opening or closing of the flaps. The microprocessor inside the stepper motor receives the instructions and converts them into pulses to operate the permanent magnet rotor.

Scheme 349

COMPRESSOR CONTROL

Using the E38 (99 MY) for this test, activation of the compressor clutch is an output control function of the IHKA module. Activation is carried out directly through a final stage (no relay required).

If the evaporator temperature is above 37°F (3°C), and the refrigerant pressure sensor indicates acceptable pressure, the control panel/module then signals the ECM that it is about to activate the compressor. The IHKA module will then activate the compressor if a cancellation signal is not received from the ECM.

Additional criteria

1. If the "snowflake" button is on at engine start-up, the control module delays compressor clutch activation until the engine speed exceeds 600 RPM for at least 5 seconds.
2. If the "snowflake" is switched off while the engine is running, the control module continues to cycle the compressor (with increasingly longer off times) for up to 15 minutes.

Compressor deactivation

Scheme 350

1. ECM detects full load - signalling IHKA
2. Evaporator temperature < 2°C
3. Coolant temperature > 120°C
4. Refrigerant pressure sensor indicates pressure is too low/high

AUXILIARY FAN CONTROL

Using a 99 MY vehicle (E38/39/46) for this test, the variable auxiliary fan is controlled by the ECM. The auxiliary fan request comes from the IHKA control module via the K-Bus. The fan speed request is based on the refrigerant pressure sensor input to the IHKA. Additional factors monitored by the ECM that influence fan operation are

1. Radiator outlet temperature sensor (exceeds the preset temperature)
2. Vehicle speed
3. Battery voltage level

The auxiliary fan motor incorporates an output final stage that activates the fan motor at variable speeds. The output stage receives an output signal (pulse width modulated 10-100 Hz) from the ECM which activates the motor.

Scheme 351

REAR WINDOW DEFROSTER

Using the E38 as an example for this test, the rear window defroster operating strategy depends upon ambient temperature.

Scheme 352

1. If ambient temperature is < 5°F (-15°C), pressing the rear window defroster but ton (ignition switch in "Run"), requests the control module to activate the defroster for 17 minutes, and then switch it off.
2. If the ambient temperature is > 5°F (-15°C), the control module activates the defroster for only 10 minutes before switching it off.
3. Reactivating the defroster by pressing the button again will give an additional 5 minutes of defrosting, regardless of ambient temperature.
4. If the ignition is switched "OFF" during defroster operation, the timer keeps operating and the defroster is deactivated. If the ignition is switched "ON" again with time remaining, the defroster is automatically reactivated until the timer runs out.
5. If the battery voltage drops bellow 11.4 volts, the defroster automatically switched "OFF", and will resume operation when the voltage rises above 12.2 volts.

WINDSHIELD BASE/WASHER SPRAY JET HEATERS

Using the E38 as an example for this test, this circuit demonstrates that both heater systems are powered by the same relay.

1. The lower portion of the windshield contains heating elements which when powered, prevent the wiper blades from freezing to the glass.
2. The washer spray jet heaters are designed to prevent ice from forming on and obstructing the washer nozzles.

The control module monitors the signal from the ambient temperature sensor (K-Bus) and automatically activates the relay in this circuit when

Scheme 353

1. Ambient temperature is < 38°F (3°C), and
2. The ignition is "ON" and
3. Battery voltage is > 12.2 volts If the ambient temperature exceeds 43°F (6°C), the windshield base/washer spray jet heaters are switched off.

PARKED CAR VENTILATION

Parked car ventilation (if equipped), operates at pre-programmed times, the IHKA control module

1. Opens the fresh air flaps, face vent flaps, and
2. Closes all other flaps, and
3. Operates the blower motor at low speed for one-half hour

Using the E38 as an example

Scheme 354

1. All switching is controlled directly by the IHKA control panel
2. Desired ventilation "ON" times are programmed into the IKE On-Board Computer (BC) using the Multi-Information Display (MID)
3. The BC in the IKE then communicates with the IHKA module over the I-Bus and the K-Bus

IHKA/ECM INTERFACES

The IHKA signals the ECM when A/C is requested (KO signal), this alerts the ECM to stabilize idle speed (EML on 750iL) and compensate for the additional load. This signal is Pulse Width Modulated (5 Hz), which informs the ECM of the "get ready" request and the anticipated compressor load. On the 99 MY (E38/39/46), the A/C on signal is transmitted via the K-Bus/CAN-Bus.

On E38/39 models, the ECM sends a reply (KOREL) signal to the IHKA control module. If input conditions are correct, the IHKA will activate the A/C compressor. In addition this separate signal circuit is used to signal the IHKA to deactivate the compressor in the event that stand still full load conditions are present.

On E46/36 models, the A/C compressor relay is activated by the ECM.

Scheme 355