Overview:
This document contains information on:
General
Function requirements
Heating mode
Switching off automatically
General
The head space heating function allows for ventilation of the driver's or front passenger's neck area with heated air. The warm air comes out of an opening below the head restraint.
The head space heating control unit controls the head space heating function depending on the following variables:
Selected heating level
Outside temperature
Soft top status
Vehicle speed
Function requirements, general
Circuit 15R
Vehicle interior temperature T < 40 °C
Function
The head space heating function is operated via the seat climate control switch group. The set heating level (1 to 3) is indicated by LEDs in the control element.
Heating mode
When switched on, the head space heating control unit actuates a heating element and a fan motor. The head space heating delays the fan motor switching on for 7 s. This prevents cold air flowing out immediately after the head space heating function is activated. For safe start-up of the fan motor, it is initially actuated for 0.5 s with the maximum control voltage irrespective of the selected heating level. To protect the heating element from overheating, the fan motor runs down to the lowest stage for 5 s when switching off.
The fan motor and heating element are controlled depending on the selected heating level. The fan motor is also controlled when the soft top is open depending on the vehicle speed and outside temperature.
Switching off automatically
If one of the following listed situations occurs, the head space heating function is automatically switched off:
Shutoff in the event of a hardware defect:
The power supply for the heating elements of the head space heating is switched off by an integrated protection relay from the rear signal acquisition and actuation module if the following circumstances coincide:
The head space heating control unit reports active actuation of the heating elements of the head space heating to the rear signal acquisition and actuation module.
There is no operating request.
Shutoff in the event of overtemperature of the printed circuit board:
Heating level 3 can no longer be activated at a printed circuit board temperature of T > 90 °C.
Heating level 3 and heating level 2 can no longer be activated at a printed circuit board temperature of T > 100 °C.
The head space heating function switched off at a printed circuit board temperature of T > 110 °C.
A fault message is stored in the fault memory if a printed circuit board temperature of T > 110 °C is reached. Manual switch on requires the affected component parts to have cooled T = 2 °C below the respective temperature threshold.
Shutoff in the event of an error (short circuit, overload or open circuit (line break)):
The head space heating control unit continuously checks the functional capability of the corresponding component parts and sends the status to the rear signal acquisition and actuation module. In the following cases, power supply to component parts is deactivated and a fault is stored in the fault memory of the rear SAM control unit:
Signal failure
Detection of a short circuit
Detection of an open line
Shutoff during engine starting procedure:
The heating elements and fan motors are switched off during the starting procedure of the engine. The LEDs in the control element remain switched on for the selected heating level.
Switching off by energy management:
In order to prevent the battery from discharging in all driving cycle phases, the state of charge is continuously evaluated. Depending on the situation, the head space heating function is also deactivated if necessary.
If the head space heating function is deactivated, the LEDs remain switched on initially. If the on-board electrical system reaches its on-board electrical system voltage within 3 min, the head space heating function also starts automatically. If the shutoff takes longer than 3 minutes, the LEDs are also switched off. If the shutoff continues and the function is requested again, the LEDs illuminate for 1.5 seconds and then they go off.
Shutoff after circuit 15R OFF:
For circuit 15R OFF and circuit 15C ON, the timer control runs on for another 5 minutes. If circuit 15R is switched on again, the head space heating function is also switched on again.