GF83.70-P-4202TX STH Heater Unit, Component Description

GF83.70-P-4202TX STH Heater Unit, Component Description
- with CODE (228) Stationary heater

Component Identification:

Location
The STH heater unit is located in the front area of the right wheelhouse.

Design
The components that are needed for generating and transferring heat are integrated in the STH heater unit:
^ Temperature sensor (A6b1)
^ Combustion air blower (A6m2)
^ Stationary heater control unit (A6n1)
^ Glow pin unit flame monitor (A6r4)
^ STH switchover valve (A6y1)
^ Heat exchanger
^ Burner housing

Function
Starting, controlling and stopping heating operation is controlled by the integrated STH control unit.

Start heater operation
The combustion air blower is actuated. It delivers at approximately its maximum speed.
The glow pin of the glow pin unit flame monitor is switched on. The preheating time of approx. 30 s starts. After the preheating time the combustion air blower is switched off for 3 seconds and the STH fuel metering pump (Y23) starts to deliver fuel.
The combustion air blower starts up again. Within about the next 60 seconds, the combustion air blower and the STH fuel metering pump increase their speed and output to full load. The fuel and the combustion air form the fuel/air mixture in the burner housing.
Once the increase in the flow of combustion air and fuel delivery is complete, the glow pin of the glow pin unit flame monitor is switched off and the flame monitoring safety period starts for approximately 45 seconds.

At the end of the safety period, the glow pin unit flame monitor signals the following in its function as a flame monitor:
^ "hot": sufficient combustion heater operation continues.
^ "cold": flame formation is nonexistent or inadequate - the STH fuel metering pump is switched off and another attempt is made to start (once only).
If the second attempt to form a flame also fails, the fuel supply is shut off by switching off the STH fuel metering pump and a fault shutoff with combustion air blower run-on takes place.

Heating mode
Heater operation is controlled automatically depending on the coolant temperature. Possible statuses:
^ Full load operation
^ Partial load operation:
^ Control interval
The formation of a flame during heating operation is monitored by the glow pin unit flame monitor.

If the flame blows out, another attempt is made to start (once only). If the second attempt to form a flame also fails, the fuel supply is shut off by switching off the STH fuel metering pump and a fault shutoff with combustion air blower run-on takes place.

The STH switchover valve is closed at coolant temperatures of less than 60 °C (small coolant circuit). From a temperature of 60 °C it is pulsed and the larger coolant circuit is also heated.

Overheating protection
The internal temperature sensing of the STH control unit detects overheating (actuation temperature 125 °C) and activates a heater unit fault shutoff with subsequent fault interlock for approximately 120 seconds.

Terminate heater operation
The combustion is terminated by switching the STH fuel metering pump off.
The combustion air blower run-on time starts.
The run-on time and the speed of the combustion air blower depend on the mode that the STH heater unit was in when it was switched off.