PRE-RELEASE
Heated front seat
| Heated front seat |
| Note | ||
|
Cars from the factory are manually programmed. |
The preconditions are that the engine is running and fan speed OFF is not selected. See User programming .
The heating pad consists of two circuits, one circuit is the heating element and the other circuit provides information on current temperature. The temperature sensor consists of an NTC resistor whose resistance varies with the temperature in the heating pad.
| Description of operation |
The ACC unit supplies the heating element with a B+ voltage from K2 pin 1 which is then grounded via G 14. The heating element in the passenger seat is supplied with a B+ voltage from K2 pin 6 and is grounded via G 24.
The temperature sensor (254) is grounded internally in the ACC unit via K1 pin 23 for both driver's seat and passenger seat
The driver's seat sensor is supplied from K2 pin 4 with 5V via a 6.8 KΩ resistor built into the ACC unit. The characteristics of the NTC resistor mean that resistance decreases afterwards as the temperature increases. This means that the voltage measured over the resistor will at the same time decrease during rising temperatures.
The passenger seat sensor is supplied from K2 pin 5 with 5V via a 6.8 KΩ resistor built into the ACC unit. The characteristics of the NTC resistor mean that resistance decreases afterwards as the temperature increases. This means that the voltage measured over the resistor will at the same time decrease during rising temperatures.
The voltage value from the sensor is A/D converted and is then available in digital form. The digital voltage value is then converted to temperature and is added to the ACC unit's operating memory. Voltage values close to 0 or 5V are interpreted as faults in the circuit.
Manual control
Repeatedly pressing the button produces the desired temperature level. The selected temperature is started and confirmed by the LED in the button. See table.|
Level
|
Indication in button
|
Temperature
|
|
1
|
1 LED
|
31°C
|
|
2
|
2 LEDs
|
40°C
|
Automatic control
The ACC control module decides whether seat heating is required. At an outside temperature of <15°C, and with a seat cushion temperature of <20°C, the heated seat will be activated. Irrespective of the temperature selected by the ACC only one LED will come on. When the ACC unit does not detect any requirement for seat heating then the heating is switched off and the LED goes out.If the passenger seat is unoccupied then the LED for the seat will be off, but the seat heating is activated until the seat temperature is reached.
|
Level
|
Indication in button
|
Temperature
|
|
1
|
1 LED
|
AUTO
|
|
2
|
2 LEDs
|
AUTO
|
