Additional rear heating and air conditioning system IHKA

The IHKA (Integrated Automatic Heating and Air Conditioning system) can be extended to include an additional rear heating and air conditioning system as an option. This serves to maximize the cooling output in the rear compartment when required (MAX AC function).

Function

An evaporator control box (without own software) is used to control the evaporator of the rear air conditioning unit and change over the rear fan control voltage from the standard rear compartment fans (under the front seats) to the rear compartment air conditioning fan.

The MAX AC function can be activated for each side separately if:

• the IHKA control module is coded accordingly
  
• Temperature at minimum limit position
  
• the rear fan control voltage is not equal to zero
  This condition includes the following conditions:
  
  • Production, transport and workshop mode not active
    
  • Signal ”control peak reduction priority” from power module not at 1, 4 or 5
    
  • Ignition (terminal 15) on
    
  • Starter (terminal 50) not active
    
  • No overvoltage
    
  • No alarm deactivation
    
• Air-conditioning function active
  

The active status is indicated as follows:

• Rear control is off:
  
  • Standard rear compartment fan is off
    
  • Rear compartment flap and rear mixer flap are closed
    
  • Outer and center console rear ventilation flaps are closed
    
• Additional rear air conditioning unit is on:
  
  • The IHKA switches the control outlet MAX AC rear to active. This activates the evaporator control in the evaporator control box.
    
  • The control voltage for the rear compartment air conditioning fan is generated by the IHKA depending on the position of the air flow potentiometer and sent to the output for rear fan control voltage. The evaporator control box switches the fan control voltage via a relay through to the rear compartment air conditioning fan.
    
  • The user specifications by means of the rear ventilation flap controllers now control the rear air conditioning flap modules for the outside and center console.
    

The MAX AC function is deactivated if one of the above activation conditions is no longer met. The evaporator valve and the rear air conditioning flaps are closed. The rear compartment air conditioning fan is switched off.

Components

The evaporator control box consists of two two-point regulators, 4 power drivers and switching logic for the fan (separate assembly).

The rear air conditioning units each consist of a blower motor, a blower control, an evaporator and an evaporator temperature sensor. The evaporator receives the required amount of refrigerant across a combination valve (expansion and shut-off valve). The rear refrigerant circuit is linked to the front air conditioning unit. The shut-off valve is supplied permanently via terminal 15. If there is a risk of freezing (evaporator temperature < 1 °C), the two-point control switches off the combination valve.

The additional rear air conditioning units are linked across additional air ducts to the air circuit of the air conditioning system. To change over between the standard air conditioning of the rear via the IHKA and MAX AC function via the additional rear air conditioning unit, four additional flap modules are fitted.