IHKA Principle of Operation
IHKA Principle of OperationAUTO Mode
The following examples will be observed when operating the air distribution and the blower controls:
^ A high blower speed is set manually by the blower knob.
^ When AUTO mode is selected, as the result of the previous manual setting, the rotary knob is still set to high.
^ Due to AUTO mode, the blower runs at medium speed.
^ If the blower output is now to be increased slightly by turning the knob to the right, a very large change occurs with the blower output.
Automatic Temperature Control
The temperature is controlled by mixing:
^ Outside air that flows through the evaporator = cold air
^ Outside air that initially flows through the evaporator and then through the heat exchanger (reheat) = warm air
While mixing the air, the IHKA temperature control determines a set position for the mixed air flap to maintain the requested interior temperature. This set position is determined from the inputs of:
^ Vehicle interior temperature sensor
^ Temperature sensor, mixed air
^ Evaporator temperature sensor
The outside temperature and the coolant temperature are also used (transferred via K-bus from the instrument cluster).
Automatic Air Distribution Control
There are 2 setting options for the air distribution:
^ Individual setting of the air distribution
^ Automatic air distribution (AUTO button)
The function light in the rotary knob for air distribution goes out when the AUTO button is pressed. The IHKA control module sets the optimum air distribution corresponding to various inputs. Automatic blower mode remains active if the air distribution rotary knob is turned manually during automatic air distribution. The function light in the AUTO button goes out.
Automatic Air Volume Control
The air volume is controlled based on the position of the fresh air/recirculating air flap and the blower speeds. The fresh air/recirculating air flap (a total of 3 individual flaps) is powered by an actuator.
The recirculating air mode is activated by pressing the AUC/recirculating air button. The fresh air inlet is closed and the recirculating air channel opened. Air volume control features a dynamic pressure compensation function.
The automatic blower and flap function as well as the function LED AUTO is activated by pressing the AUTO button. The IHKA control unit sets the optimum blower speed and position of the fresh air/recirculating air flap depending on various inputs.
Special Functions
MAX AC
The MAX AC function allows the user to request maximum cooling capacity with the simple push of a button. The prerequisite is that the outside temperature is > 50°F. The MAX AC function is deactivated by pressing another button or turning a rotary knob.
In the MAX AC function, the blower speed can be adjusted manually without exiting the MAX AC function. When ending the MAX AC function, the settings that were active before MAX AC are resumed.
The A/C compressor remains switched on after ending the MAX AC function. Exception: The A/C compressor is switched off when the MAX AC function is switched off via the A/C button.
DEFROST
Under certain circumstances the windows can fog up while driving (high humidity levels in the vehicle interior). The DEFROST function can quickly remedy this situation by preventing misting of the front field of vision. The DEFROST function assumes a higher ranking role in air distribution control.
The DEFROST function can be activated as required even when IHKA is switched off (blower zero position). The blower runs at full power. The blower output can be adjusted manully in OFFR().-T marls
If KL15 is switched OFF with the DEFROST function active, the DEFROST function is activated again KL15 is switched "ON" within the after running period (10 minutes).
The defrost function is deactivated by pressing another button or turning a rotary knob. When ending the DEFROST function, the settings that were active before DEFROST are resumed.
AUC/Recirculating Air
Automatic recirculating air control (AUC) is a standard feature on (E85) Z4 vehicles with IHKA. Initially, the AUC function is activated when the AUC/recirculating air button is pressed in fresh air mode.
Pressing the button again activates the recirculating air mode. Pressing the button once again returns to fresh air mode. Recirculating air mode and AUC mode are indicated by green function lights (LEDs) on the control panel.
As was the case with previous heating/air conditioning systems, the AUC/recirculating air function also features "forced ventilation with fresh air," the activation and duration of which depends on whether the system is in A/C mode (compressor active). The fresh air is already dehumidified if the A/C compressor is ON, therefore, the duration of recirculating air mode is longer.
Forced ventilation cycles:
Cold Start Interlock
The cold start interlock function intervenes in activation of the air distribution flaps and blower control. The cold start interlock is active at low outside temperatures and low coolant temperatures (engine cold) to prevent cold air distribution until warm air is available.
In the (E85) Z4, the cold start interlock is not deactivated by a terminal change from KL15 ON to OFF. When the switch on conditions are fulfilled, the defrost air distribution flap is fully opened and the ventilation and footwell air distribution flaps are completely closed. As a result, no cold air is blown directly at the driver/passenger.
The automatic blower function must be selected for intervention in blower control.
Cooling Mode
Cooling mode serves the purpose of cooling a heated vehicle by forced air recirculation at high outside temperatures. Cooling mode is active during engine start and applies both in AUTO mode and manual mode. The A/C compressor must also be activated.
Cooling mode supersedes the AUC function. If the signal from the AUC sensor specifies fresh air mode, recirculating air mode is retained or set to a fresh air share of 20% when cooling mode is active.
An (E85) Z4 feature is that cooling mode is extended from 12 to 15 minutes in tropics coding (hot country). When the control variable (y-factor) is below -90%, the fresh air/recirculating air flap is set to recirculating air for maximum 12 minutes. As a result, warm air is not blown directly at the driver/passenger.
After this period of 12 minutes has elapsed, if the control variable is below -90%, the fresh air/recirculating air flap is set to 20% fresh air.
Avoiding Fogging During Start
This function is activated once with KL15 ON in automatic mode. The prerequisite is that the outside temperature is above 32°F. The defrost air distribution flap is closed for 12 seconds. Consequently, windshield fogging caused by moist air from the evaporator is avoided.
This function is superseded by the cold start interlock. In this case, all air distribution flaps are closed.
Dynamic Pressure Compensation
To prevent uneven air volume as driving speeds vary, dynamic pressure is compensated by the fresh air flap reducing the fresh air inlet opening as the vehicle speed increases. The vehicle speed is made available via the K-bus from the instrument cluster. The fresh air flap reduces the opening angle within a certain speed range according to a characteristic curve. The calculation of the flap position is dampened to avoid continual flap activation as a result of variations in vehicle speed.
Electric Cooling Fan
The electric cooling fan is activated by the ECM that outputs the control voltage for the final stage of the fan. Activation for the correct fan speed (15 speeds) is derived by the IHKA control module from the refrigerant pressure sensor signal and sent to the ECM.
