STH control unit, component description - GF83.70-P-4200SX

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

Shown on model 221.0

Fig 1: Identifying STH Control Unit

Courtesy of MERCEDES-BENZ USA

Location

The STH control unit is integrated into the STH or HB heater unit (A6) on model 221 or into the STH control unit (A6) on model 216, which is located in the rear area of the right wheel well.

Task

The STH control unit regulates the STH heater unit's heater operation, thus heating the interior as programmed. It also monitors the components involved in the heater operation.

Reading the following sensors:

Glow pin unit flame monitor (A6r4)
Temperature sensor (A6b1)
Thermal fuse (A6f1)

Control and voltage supply:

Glow pin unit flame monitor
Combustion air blower (A6m2)
Fuel preheating system (A6r5) (for diesel engine)

Discrete inputs

Circuit 30
Circuit 31
STH radio remote control receiver (A6/1)

Discrete outputs

STH or AUH fuel metering pump (Y23) (model 221),
STH fuel metering pump (Y23) (model 216)
STH switchover valve (Y16)
STH radio remote control receiver (model 221 as of 1.6.06, model 216)

CAN signals

The STH control unit is connected to the interior CAN for exchanging data.

Emergency shutoff

If the temperature of 125 °C is exceeded in the heater unit, then the heater unit is permanently switched off via the thermal fuse.

Heater/ventilation duration

The heating period can be configured using STAR DIAGNOSIS (basic value = 50 min). The ventilation duration can be shortened relative to the heating duration (25, 50 or 75%).