Component Description and Operation
COMPONENT DESCRIPTION AND OPERATIONDCHA Assembly
The DCHA is a supplemental heater designed to pre-heat the engine's coolant in order to supply the vehicle's occupants with heat prior to the engine reaching operating temperature. The DCHA assembly mounts underneath the vehicle on the left side floor pan near the front door opening. The DCHA assembly connects to the vehicle's heater hoses and has a fuel supply line that connects to the vehicle's fuel tank.
The DCHA assembly consists of a:
- combustion air fan assembly
- burner housing
- burner insert
- control unit/heat exchanger
- combustion chamber
- dosing pump
Combustion Air Fan
The combustion air fan assembly includes the:
- combustion air fan
- combustion air fan inlet
- fuel supply inlet
The combustion air fan delivers the air required for combustion from the combustion air inlet to the burner insert.
Burner Housing
The burner housing includes the:
- coolant inlet
- coolant outlet
- exhaust outlet
The burner housing accommodates the burner insert and is combined with the control unit/heat exchanger as an assembly.
Burner Insert
The burner insert includes the:
- combustion pipe fuel cross section
- glow plug/flame sensor
Inside the burner insert, fuel is distributed across the combustion-pipe fuel cross section. Combustion of the fuel/air mixture takes place within the combustion pipe to heat the exchanger. The glow plug/ flame sensor, located in the burner insert, ignites the fuel/air mixture during heater start up. After heater start up, the glow plug/flame sensor operates in the flame sensor function. The glow plug/flame sensor is an electrical resistor by design, and is located in the burner insert opposite the flame side.
Control Unit/Heat Exchanger
The control unit/heat exchanger includes the:
- control unit
- temperature sensor
- overheat protection
- heat exchanger
- connector terminal
The control unit controls and monitors combustion operation. The control unit is ventilated by means of a ventilation hose routed from the combustion air collector compartment of the burner. The heat exchanger transfers the heat generated by combustion to the coolant circuit. The control unit/ heat exchanger and the burner housing are an assembly and must not be disassembled.
The temperature sensor senses the coolant temperature in the heat exchanger as an electrical resistance. This signal is sent to the control unit for processing.
The overheat protection, controlled by the temperature resistor, protects the heater against undue operating temperatures. The overheat protection will switch the heater off if the water temperature exceeds 105 °C (221 °F).
Dosing Pump
The dosing pump is a combined delivery, dosing, and shut-off system for the fuel supply of the heater. The dosing pump receives its supply of fuel from the vehicle's fuel tank.