Climate Control, Basic Function - GF83.00-P-9901A

MODEL ALL (CAR) 

Overview 

This document contains information on:

• General
• Function requirements
• Recording and evaluation of variables
• Actuation of air conditioning components

General 

The climate control system is controlled according to the following criteria:

• Settings on the air conditioning control panel or the multimedia system control
• Variables (registered by various sensors)

The climate control controller regulates the following properties:

• Air temperature (heating/cooling)
• Air humidity (humidify/dry)
• Air components (filtering/exchange)
• Air speed (blower control)

Depending on the vehicle model, the climate control system is controlled via various control units:

• Climate control unit
• Central controller unit (SAM)

The climate control controller is networked with the on-board electronics. This means it can incorporate relevant influences for the control. The control quality is therefore improved and energy consumption is reduced.

The tasks of the climate control controller are:

• Recording and evaluation of variables
• Actuation of air conditioning components
• Shift point adjustment with transmission 725 (not in hybrid vehicles)
• Control of operating modes (e.g. fresh air/air-recirculation mode, evaporator drying, etc.)

Function requirements 

• Circuit 15 on (not for residual heat utilization or heating mode request from stationary heater)
• Climate control switched on

Only for cooling mode:

• Refrigerant compressor switched on (A/C function)
• Engine running.

Recording and evaluation of variables 

The climate control controller registers the following variables and evaluates them:

• Interior temperature in head area

  The interior temperature in the head area is registered by a temperature sensor in the overhead control panel and is transmitted to the climate control controller.

• Outside temperature

  The outside temperature is registered by the outside temperature sensor and is transmitted to the climate control controller.

  If the vehicle is stationary, the measured temperature can differ considerably from the actual outside temperature. The outside temperature is only incorporated into the interior temperature regulation, when the vehicle speed is more than 20 km/h. At speeds below 20 km/h and when the ignition is switched off and on, the climate control controller uses the last measured temperature value.

• Temperature at the air outlets in the vehicle

  The climate control controller receives the information from the outlet air temperature sensors and uses it to regulate the outlet air temperature.

• Temperature and moisture on windshield

  In the rain and light sensor with additional functions, the relative air humidity is registered directly at the windshield. If the probability of window fogging is high, the climate control controller increases the blower setting. If automatic engine start/stop is active, the climate control controller can prevent an automatic engine stop. In the case of impending window fogging during an engine stop phase, the climate control controller can cause the engine to start and activate the refrigerant compressor.

• Coolant temperature

  The combustion engine control unit calculates the coolant temperature and transmits a corresponding signal to the climate control controller. The coolant temperature is used to control the air mixing flaps and to actuate the coolant circulation pump.

• Evaporator temperature

  The climate control controller receives the information from the evaporator temperature sensor. If the evaporator temperature drops to approx. 2 °C, the refrigerant compressor shuts down. This prevents the evaporator from icing up. As of an evaporator temperature of 2.5 °C, the refrigerant compressor cuts in again.

• Refrigerant pressure

  The climate control controller receives the value from the refrigerant pressure sensor and compares it with a stored temperature/pressure curve. If the refrigerant pressure is below 0.8 or above 28 bar, the refrigerant compressor shuts down or does not switch on.

• Solar radiation

  The climate control controller receives the information from the rain and light sensor with additional functions and regulates the interior temperature accordingly. In the sun is shining in on one side, it sets an adequate temperature difference between the left and the right specified control temperatures.

  If the sun is shining into the vehicle from the side or from the rear and also at an acute angle, the sun sensor provides imprecise values. This is why a sun sensor is virtually realized in the rear passenger compartment. The multimedia system control sends the time and location information (with the aid of the GPS signal) to the climate control controller. The climate control unit references the values from the sun sensor at the windshield and adapts the temperature control accordingly.

• Vehicle speed

  The instrument cluster control sends the speed signal to the climate control controller. The vehicle speed is used to regulate the ram air and for the internal calculation of the outside temperature, e.g. while stationary.

• Engine speed

  The combustion engine control unit determines the engine speed and transmits the information to the climate control controller. It is used among other things for controlling the refrigerant compressor.

• Door status, position of side windows and sliding roof

  The corresponding control units register the information and transmit it to the climate control controller.

  When a door, the windows or the sliding roof is open, the climate control controller references the values of the interior temperature sensor and adjusts the temperature control accordingly. This prevents any unnecessary readjustment in the event of high temperature differences between the inside and outside air.

• Air quality (depending on equipment)

  The climate control controller receives the information from the air quality sensor. If the concentration of pollutant gas is high, air-recirculation mode activated.

Actuation of air conditioning components 

The climate control controller actuates the following climate control components:

• Electronic blower motor

  The electronic blower motor drives a radial blower in the air conditioner housing. It is actuated according to the respective settings on the air conditioning control panel.

• Refrigerant compressor

  Via the regulation valve, the climate control controller regulates the refrigerant compressor steplessly up to 100 %.

  The climate control controller also transmits the calculated torque of the refrigerant compressor to the combustion engine control unit. This keeps the idle speed constant in accordance with the additional load that occurs when the refrigerant compressor is switched on.

• Actuation of fan motor (engine fan)

  The climate control controller calculates the target fan speed depending on the refrigerant pressure and transmits this information to the combustion engine control unit.

• Actuation of PTC heater booster (with certain engines and equipment features)

  The climate control controller activates the PTC heater booster as required. This heats up the vehicle interior up more quickly.

• Actuation of coolant circulation pump

  To guarantee the heat output at low engine speeds or when the engine has stopped, the coolant circulation pump is also actuated.

• Actuation of the air flaps via the respective actuator motor

  Air flaps in air conditioner housing:

  • Air distribution flaps
  • Fresh air/recirculated air flap
  • Left air mixing flap (temperature control)
  • Right air mixing flap (temperature control)

Additional air flaps depending on vehicle equipment:

• Rear passenger compartment air mixing flap
• Left footwell/center air vent/side air vent and rear air vent flap (ventilation control)
• Right footwell/center air vent/side air vent and rear air vent flap (ventilation control)
• Left B-pillar air distribution
• Right B-pillar air distribution

In the equipment variant with air quality package, the climate control controller also actuates the following climate control components:

• Driver side air vent ionizer
• Perfume atomizer generator

	Further basic functions
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	Control units
	Central controller unit, basic function		GF54.21-P-9895A
	Components
	Air conditioner housing, basic function		GF83.40-P-2015A
	A/C operating unit, basic function		GF83.40-P-2016A
	Expansion valve, basic function		GF83.40-P-2018A
	Outlet air temperature sensor, basic function		GF83.40-P-2019A
	Circulation pump, basic function		GF83.40-P-2020A
	Refrigerant pressure sensor, basic function		GF83.40-P-2021A
	Air quality sensor, basic function		GF83.40-P-2022A
	Mechanical refrigerant compressor, basic function		GF83.55-P-2001A
	PTC heater, basic function	Model 177 with engine 608, 654	GF83.70-P-2009A