Activate heater with stationary heater switch, function - GF83.70-P-3066SX

MODEL 221.0 /1, 216.3 with CODE (228) Stationary heater up to Model Year 8

Fig 1: Identifying Heater With Stationary Heater Switch Function Diagram

Courtesy of MERCEDES-BENZ USA

Function requirements:

Circuit 30
Sufficient remaining quantity of fuel in tank

Function

When the stationary heater button is pressed, the upper control panel control unit forwards the switch-on signal via the interior CAN to the STH control unit. This then starts a "ventilate or heat" query via the interior CAN to the AAC [KLA] control unit. The AAC [KLA] control unit determines the current interior and outside temperature. Depending on the values determined and the last setting of the AAC [KLA] control unit, the AAC [KLA] control unit makes a decision either for heating or ventilation and then transmits the decision to the STH control unit.

If the decision is for heating, a query on the status of all components involved in the heater operation is conducted and a self-test is performed if required. The heater operation is not started in the event of a relevant fault. However, the stationary ventilation function is always performed, irrespective of the result.

Heating decision

The fuel metering pump is actuated to supply fuel and the heater unit starts heater operation.

To enable the interior to be heated up faster, the heater unit regulates the flow of coolant depending on the temperature between the small and large coolant circuit via the STH switchover valve. The coolant circulation pump ensures that the temperature-controlled coolant is circulated in the coolant circuit.

When the temperature is at a sufficient level, the AAC [KLA] control unit actuates the blower motor via the blower regulator.

Ventilation decision

During stationary ventilation only the blower is actuated in the vehicle.

The AAC [KLA] control unit actuates the blower motor via the blower regulator.

Depending on the interior temperature, a switchover from stationary heating to stationary ventilation and vice versa can be made.

Status indicator

The red indicator lamp in the STH button indicates stationary heating, and the blue lamp indicates stationary ventilation.

STH heater unit component description	A6	GF83.70-P-4202SX
STH control unit, component description	A6n1	GF83.70-P-4200SX
Blower, component description	A32m1	GF83.10-P-2050SX
Blower regulator, component description	A32n1	GF83.10-P-2051SX
COMAND controller unit, component description	A40/3 On vehicles without code (494) USA version	GF82.85-P-3136SX
COMAND controller unit, component description	On vehicles with code (494) USA version	GF82.85-P-3136SXU
Cockpit central display, component description	A40/8	GF54.30-P-6100SX
In-car temperature sensor, component description	B10/4	GF83.57-P-2127SX
Outside air temperature sensor, component description	B14	GF83.57-P-4000SX
Coolant circulation pump component description	M13	GF83.75-P-2110SX
Driver-side SAM control unit with fuse and relay module, component description	N10/1	GF54.21-P-6010SX
Automatic air conditioning control unit, component description	N22/1	GF83.40-P-3012SX
Upper control panel control unit, component description	N72/1	GF54.21-P-6040SX
Central gateway control unit, component description	N93	GF54.21-P-4170SX
STH switchover valve component description	Y16	GF83.70-P-4205SX
STH fuel metering pump component description	Y23	GF83.70-P-4203SX