In diesel vehicles which give off little residual heat, a booster heater is used to heat the passenger compartment rapidly in the case of low ambient temperatures.
When the passenger compartment temperature is set to HI at the climate control assembly or the heater control is set the highest level, the Electronic Automatic Temperature Control (EATC) transmits an “electric booster heater ON” request signal to the Generic Electronic Module (GEM) via the MS CAN bus. If a manual air conditioning system is installed, the signal is transmitted via a conventional cable connection.
The electric booster heater consists of three individual heating elements, which are incorporated into a single housing.
The electronics of the electric booster heater controls three output stages dependent upon a pulse width modulation signal (PWM), which is generated by the GEM. The output stages switch the three heating elements of the electric booster heater ON or OFF individually, whereby the heating periods of the individual elements can overlap. Due to the variable switch-on duration, continuously variable temperature control is possible. The overall heating power of the three heating elements is linearly proportional to the PWM signal. If the PWM signal is below 10% or above 95%, the electric booster heater is not activated.
The electric booster heater is switched off when an engine coolant temperature of 70°C or an ambient air temperature of 20°C is exceeded.
