Heating and A/C Functions Part 1

Heating And A/C Functions

The IHKA integrated automatic heater -A/C system has the following functions:
Blower
- Air distribution
- Recirculated air
- Temperature control
- Automatic recirculated air control
- Operation
- Wiper rest heating
- Rear-window defroster (demister)

The IHKA is used to adapt the in-car climate to the individual needs of the passengers. A Basic or a High version of the IHKA is fitted for this purpose. Information is exchanged between the vehicle components and the IHKA via the K-CAN SYSTEM data bus.

As additional special equipment for the High version of the integrated automatic heating / air conditioning system (IHKA), rear air conditioning (FKA) with integrated cooler box can be fitted.

The FKA is connected to the refrigerant circuit of the IHKA via two shut-off valves and a pressure and suction line. The shut-off valves are located in front of each evaporator and are only fitted if an FKA is fitted. The shut-off valves can only be activated by the FKA if the IHKA has been coded to "FKA is fitted".

NOTE: Without coding the IHKA to "FKA is fitted", the shut-off valves are without current and remain closed. In this case, damage is possible.

Brief description of components

DME Digital Engine Electronics
The IHKA control system informs the Digital Engine Electronics via the K-CAN data bus of the activation status of the compressor. The compressor is activated by the IHKA if no shutdown criterion (e.g. excessive coolant temperature or kickdown mode) prevents such an activation. When the compressor is activated, it is possible to switch between operation with and without an increase in idle speed.

The idle speed is increased at an
- outside temperature of = 15 degrees C and a
- setting for controlled variable Y on left or right = 10 %.

The idle speed is not increased at an
- outside temperature of = 13 degrees C and a
- Setting for controlled variable Y on left or right = 20 %.

IHKA control module
The IHKA control module records the signals of the IHKA components and controls/regulates the heating and air conditioning process. The IHKA control module causes the rear-window defroster to be activated and deactivated by the power module. The output stage for the rear roller blind is also incorporated in the IHKA control module. The IHKA control module comes in four versions: Basic and High versions with and without rear window roller blind output stage.

LM Light Module
The LM light module provides the IHKA with information on the dimming setting and the light status (e.g. low beam activated). The IHKA controls the brightness of the function and locator lights in accordance with this information.

PM Power Module
The power module monitors the battery charge state and the open-circuit current consumption of the car. It also activates or deactivates the rear-window defroster depending on activation by the IHKA. In addition, the trunk lid lock is controlled via the power module. Information is received and sent via the K-CAN PERIPHERALS data bus.

Control panel and control display
The control panel with control electronics is inserted into the instrument panel. The control panel features only the most important control elements. The "HAZARD WARNING FLASHERS" and "CENTER LOCK" (central locking) buttons are also accommodated. These button functions are not evaluated by the IHKA control system. The connections are looped through on a hardware basis.

There are different control panels for the Basic and High versions of the IHKA. The control panel of the basic version is not delivered with an OFF function. This function, however, can be coded per Car Memory.

The control display (on-board monitor) is built into the instrument panel. Precision adjustments of the IHKA functions are carried out at the control display.

IHKA air conditioner
The IHKA air conditioner is mounted underneath the instrument cluster on the bulkhead in the middle.

The air conditioner is made up of the following components/functional units:
Evaporator/evaporator sensor
- Heat exchanger/heat exchanger sensor
- Blower with blower controller
- Flaps/flap kinematics
- Flap drives/stepping motors

The air conditioner fulfills the following tasks:
- Generation and regulation of air quantity
- Air distribution, air mixture (stratification) and air dehumidification
- Transfer of heat output delivered by coolant circuit
- Transfer of refrigerating output generated by refrigerant circuit

NOTE: When the IHKA is operated for the first time, the measures described under "Compressor" must be carried out.

Blower with controller
Blower: The blower is mounted with the blower motor as an assembly in the glovebox area. The blower can be detached from the motor. Because the blower is mounted on the passenger's side, there are different versions for LHD and RHD cars.

Controller: The controller is mounted on the blower motor housing. The controller is activated by the control electronics in the control panel of the IHKA via the MUX bus in the same way as the MUX motors and is capable of on-board diagnosis. The diagnosis information is transmitted to the control electronics for evaluation. If on-board diagnosis identifies a fault which would cause components to overheat, the current is reduced or cut off until the fault criterion has been eliminated.

The blower draws in air as a function of the flap setting either
- through the cleaners and the fresh air duct or
- through the recirculated air flap.

Air can be drawn in through both channels depending on the operating state.

Flaps with drive and mechanism
The flaps serve to distribute the air and to mix hot and cold air.

Fresh air flap: The amount of clean air drawn in by the blower is regulated with this flap. The flap is moved by a high-speed drive so that it can be closed in extra-quick time in automatic recirculated air mode (AUC mode). The fresh air flap also serves to compensate ram pressure.

Recirculated air flap: The recirculated air flap is designed as a louvre with three fins. The amount of recirculated air drawn in is regulated with this flap.

Footwell flap: In the Basic version, the footwell flap directs the air-flow into the front and rear foot wells. In the High version, the front and rear foot wells are supplied separately on the left and right.

Rear compartment ventilation flaps: The rear compartment ventilation flaps (separate on left and right) are only fitted in the High version. These flaps serve to adjust the air-flow at the rear compartment ventilation outlets and the temperature (rear compartment stratification).

Defrosting flaps: The two linked defrosting flaps serve to regulate the air-flow to the windshield. These flaps are activated jointly in all adjustment and operation functions from the driver's side only.

Hot air/cold air flaps: The hot air/cold air flaps serve to regulate the air-flow at the air inlet grills of the instrument panel and at the B-pillar vents. The temperature is also stratified with these flaps. The combination of the flap pair regulates the air-flow and the temperature simultaneously. The functions are separate on the left and right in the High version.

Flap drives/stepping motors
Different stepping motors are used for particular purposes on the flap drives.

High-speed motors: High-speed motors are only used on the fresh air flaps. The windings of these motors are activated by the control electronics with a stepping frequency of up to 500 Hz.

MUX motors: MUX motors are used on all the other flaps. MUX motors are provided with an integrated circuit for controlling the windings. The integrated circuit is bus-and diagnosis-compatible. All MUX drives and the blower control are activated by the control electronics via a common motor bus (MUX bus). Faults reported by the integrated circuits are registered in the control electronics and result in the activation being interrupted.

Each drive is furnished when manufactured with an unalterable address. This facilitates clear differentiation in bus communication. Because of their individual addresses, the motors cannot be exchanged between each other.

Condenser with integrated drier
The thermal energy generated by compression of the refrigerant gas in the heat exchanger is dissipated by air cooling to the surroundings at the condenser surface. The refrigerant condenses and turns liquid. In order to prevent corrosion damage, any water present in the refrigerant circuit is bound in the integrated drier. The drier insert can be replaced. It incorporates a filter shield to provided protection against particles.

Compressor
The compressor compresses the refrigerant gas drawn in by the evaporator and forces it to the condenser. It is always in operation when the vehicle engine is running. Infinitely output regulation is possible on account of its design and activation of a regulating valve with pulse-width-modulated signals by the control electronics. For the purpose of load reduction, only the refrigerating output that is directly needed is generated. The control and switching criteria for this purpose are:
- Compressor speed (engine speed)
- Compressor load torque (from IHKA to DME)
- Torque limitation (from DME to IHKA: possible limitation of load torque in event of kickdown operation or excessive coolant temperature)
- Refrigerant pressure limitation

Information is exchanged between IHKA and DME via the K-CAN bus.

NOTE: The compressor must be broken in without fail in the following cases:

- Initial operation of the IHKA
- Replacement of the refrigerant compressor (KMV)
- Refilling of the cooling circuit with refrigerant

Compressor breaking-in: To ensure fault-free compressor lubrication, it is necessary to mix the amount of oil added by the manufacturer uniformly with the liquid refrigerant. For this purpose, the compressor must be operated for a specific period at speed of between 300 and 1500 rpm.

If the engine idle speed exceeds 1500 rpm, the breaking-in procedure is automatically cut off and a message issued. The breaking-in procedure must then be repeated in its entirety.

Specifications: The air conditioning must be set to OFF when the engine is started. Do not switch on the air conditioning before being prompted.

Carry out the following steps:
- Set all air outlet nozzles in instrument cluster to OPEN.
- Start engine and allow idle operation to stabilize.
- Set blower output to min. 75 % of max. output.
- Switch on air conditioning and run for at least 2 minutes without interruption.

Auxiliary fan
The auxiliary fan is needed to cool the condenser. On the EURO version of the N62 engine, an electric suction fan is used. The fan characteristic curve coded for this always outputs at least stage 1 when the air conditioning system is activated. The required fan speed depends on the refrigerant pressure and is transferred by the air conditioning system across the CAN bus to the DME.

Pressure sensor
The pressure sensor in the pressure line between the condenser and the evaporator supplies the control electronics with signals relating to the system pressure.

Expansion valve
The expansion valve is attached to the evaporator. It serves to regulate the amount of liquid refrigerant injected into the evaporator. The liquid refrigerant is metered in such a way that only enough refrigerant as can be fully evaporated is admitted into the evaporator.

Evaporator
The evaporator consists of 27 aluminum plates and has a surface of approx. 5 square meters. Temperature control in the evaporator is performed by the control module. The evaporator temperature controller operates independently from the other control loops with established controlled variables. The cold air emerging from the evaporator is increased to the desired temperature with the aid of the heat exchanger.

Microfilter/air intake
A microfilter is located in both of the filter housings for the intake of air. In the Basic version, it is a particle filter while in the High version, it is a combination of particle filter and carbon canister. The carbon canister retains toxic and fouling gases.

Main functions

Temperature control
The actual interior temperature value and the setpoint interior temperature value are compared by left and right master controllers. The differential signal resulting from the comparison influences the controlled variable (Y-value) for control.

The operating range of the master controller is configured more widely than the operating range of the downstream controllers. The different IHKA functions, such as e.g. automatic flap and blower facility, are dependent on this control range.

Auxiliary control loops for the heat exchanger on the left and right correct disturbance variables. Disturbance variables can be caused by temperature changes as a result of air-flow and water flow fluctuations.

The evaporator temperature is set using a separate regulating circuit and is not a disturbance variable for the system.

Two similarly independent control loops regulate the ventilation temperature on the left and right sides. This helps to achieve a stratification between the footwell vents and the ventilation vents.

Interior control
The effective temperature range is from 16 degrees C to 32 degrees C (approx. 60 degrees F to 90 degrees F). In this temperature range, the temperature can be set in increments of 0.5 degrees C (1.0 degrees F).

MAX HEATING: At a setpoint setting of 32 degree C, MAX HEATING is activated individually for the left and/or right sides. Interior control is thereby canceled. The heat exchanger temperature is adjusted up to the maximum temperature of 90 degrees C. The controlled variable Y is set to "maximum heating".

EXCEPTION: The MAX HEATING function must be canceled so that the water valves remain closed during independent ventilation operation.

MAX COOLING: At a setpoint setting of 16 degrees C, MAX COOLING is activated individually for the left and/or right sides. Interior control is thereby canceled. The heat exchanger temperature is adjusted down to the minimum temperature of 5 degrees C. The controlled variable Y is set to "maximum cooling".

DEFROST: During this function, the interior regulation is disabled. On termination of the DEFROST function, in the same way as for the MAX AC function, the temperature is matched to normal operation. This matching prevents strong cooling following the DEFROST function.

Correction of setpoint values
Outside temperature input: The setpoint value is corrected as a function of the outside temperature. The effects of radiation from outside and surrounding surfaces of the passengers are thus compensated. The outside temperature is recorded in the fender areas by an external temperature sensor and transmitted via the K-CAN bus to the IHKA. The outside temperature input and thus specified value increase can be between +12 degrees C and -2 degrees C. The outdoor temperature input also serves as so-called pre-activation for a possible disturbance variable.

Interior temperature sensor: The control panel accommodates a temperature sensor with inside sensor fan for recording the interior temperature.

Heat exchanger control
Heat exchanger sensors: Heat exchanger sensors are installed on the left and right sides in the air-flow of the heater for recording the discharge temperature at the heat exchanger. The opening time of the water valves is derived from the values thus determined. The water valves are activated with pulse-width-modulated signals.

Filling station effect: When the valves are at zero current, the heat exchanger can fill up with water (filling station effect). To avoid this, the water valves continue to be supplied with current for three minutes after the drop in terminal 15.

Engine map cooling: Coolant temperatures of up to 120 degrees C occur due to the use of map cooling in gasoline engines. In order to avoid damage to the air conditioner, the heat exchanger temperature is restricted to 90 degrees C. If faulty water valves cause the heat exchanger temperature to exceed 98 degrees C, map cooling is deactivated in the DME via the K-CAN bus.

Auxiliary water pump: An electric auxiliary water pump is installed in order to ensure adequate water flow through the heat exchanger at low engine speeds. Activation takes place
- with the residual heat function or
- with terminal 15 ON and engine temperature ≥ 0 degree C and no blower zero setting and
- controlled variable Y (driver or passenger) ≥ 5 % or
- DEFROST or
- MAXIMUM HEATING function

Virtual ventilation flap
A virtual flap setting (i.e. does not exist in reality) is calculated in order to achieve the temperature and air volume of the total air-flow. The following influencing variables are taken into account in the calculation:
- Temperature setting of passengers (controlled variable Y)
- Stratification setting
- Ventilation temperature (actual value)
- Solar radiation (solar sensor with High version only)
- Outside temperature
- Flap curves for footwell
- DEFROST ON/OFF
- Established correction factors
- Temperatures of evaporator and heat exchanger

The settings of the cold and hot air flaps are corrected with the virtual flap setting calculated from the points listed. The correction is carried out in such a way that the desired air volume and temperature is reached at the air inlet grill through the mixture of hot and cold air.

The settings of the hot and cold air flaps determine the hot and cold air mass flows individually. They thus determine the total mass flow in addition to the ventilation temperature.

In this system, each change in the opening of a flap influences the temperature and the air-flow in the overall system. In the correction of the disturbance variables, a distinction must be made between the High and Basic versions. On the basic version, there is only one ventilation temperature sensor. The stratification setting can only be made from the driver's side. The hot and cold air flaps are adjusted with bus-controlled step motors.

In the automatic program, the virtual flap position depends only on the following influencing variables:
- Temperature setting of passengers
- Solar radiation (solar sensor with High version only)
- T (outside temperature)
- T (passenger compartment)

The real flap angle is then calculated from:
- Virtual flap position
- T (ventilation) TARGET (stratification setting)
- T (ventilation) ACTUAL
- T (heat exchanger)
- T (evaporator)

Ventilation control (stratification), rear compartment
This function is only available in the High version . The stratification flaps for the rear compartment are separate. The left and right stratification flaps fulfill the following tasks:
- Shutting off of the air-flow to the vents when the shutoff flaps on the vents are manually closed.
- Control of the discharge temperature in the rear compartment through mixture of hot and cold air

The rotational angles of the stratification flaps result in the following influence on the air stream:

Rotational angle Influence on the air stream
0% CLOSED
56% Warm
100% Cold

Air volume control
Automatic blower and flap settings: The automatic blower and flap facility for the relevant side is activated by operating the left or right AUTO button or after an appropriate prompt by the control display. The associated AUTO function LED is activated. An automatic blower facility dependent on the blower control (Y-value) is activated simultaneously.

The automatic blower facility on the relevant side is deactivated when the blower control is actuated. The automatic flap facility remains active.

Pressing the AUTO button returns the system to the automatic blower facility for the relevant side.

The current blower output is only indicated in manual mode in the control display.

The automatic fan control is dependent on the variable (Y) and the signal of the solar sensor.

Automatic blower increase: Automatic blower increase is available with manual flap setting and automatic flap facility.

The normal setting range is extended so that the car interior can be rapidly cooled down or heated up at extreme inside temperatures.

The automatic blower facility is only dependent on the blower control (Y-value) on the driver's side.

Manual blower setting: The blower output is increased by turning the blower control clockwise. The blower output is reduced by turning the blower control counterclockwise. The set blower stage is indicated in the control display by a bar display.

In the High version, the blower can be adjusted with two potentiometers separately for the left and right sides. In the Basic version , this can be performed with a potentiometer on the left side.

The potentiometers do not have stops. Adjustments are made in increments of one stage per notch. The newly set blower value is indicated without delay in the control display. Continuing to turn the potentiometer has no effect once the maximum or minimum setting has been reached.

Ram pressure compensation: As driving speed increases, the air-flow at the air inlet ducts increases over proportionally without ram pressure compensation. This effect can be compensated by reducing the air inlet ducts with the fresh air flaps. For this purpose, the opening angle of the fresh air flaps is altered as a function of the driving speed and the blower setting between 100 % and 30 %.

Electrical-system-dependent blower control: If necessary, priority stages for reducing the blower output are transmitted by consumer deactivation of the power module via the K-CAN bus.

Influence of terminal 50: In order to relieve the load on the car battery during the starting sequence, the blower is switched to OFF as long as terminal 50 is ON.