SL 500 (230.475) V8-5.0L (113.963) (2004)
Component Identification
Function sequence
1. At a coolant temperature of greater than 72 °C and less than 77 °C the STH heater unit (except model 220) or the STH or HB [ZUH] heater unit
(model 220) operates in partial load mode.
2. The STH fuel metering pump or the STH or HB [ZUH] fuel metering pump (Y23) and the combustion air blower (A6m2) operate at a low output
and rotational speed. The circulation pump (A6m1) delivers the coolant via the heat exchanger (2) and the heating and cooling circuits. The
blower motor feeds preheated air into the interior.
3. Due to a malfunction, the coolant temperature in the STH heater unit or in the STH or HB [ZUH] heater unit increases to the impermissible
temperature value of 105 °C.
4. The internal temperature sensing of the STH control unit or the STH or HB [ZUH] control unit (A6n1) recognizes the overheating and activates
for approx. 120 s the heater fault run-on period with subsequent fault interlock.
5. The STH fuel metering pump or the STH or HB [ZUH] fuel metering pump (Y23) is switched off and the control and operating unit (N18, N22 or
N22/7) is actuated via CAN-B (CANpump B) with the signal "Blower off".
6. The control and operating unit (N18, N22 or N22/7) switches the blower motor off and switches from stationary heating mode to normal operating
mode.
7. At the end of the fault run-on period, the combustion air blower (A6m2) and the circulation pump (A6m1) are switched off. The indicator lamp in