Webasto Product N.A., Inc. 12 www.techwebasto.com
GENERAL DESCRIPTION DBW 2010/2020/300 COOLANT HEATERS
2.1 PARTS OF THE HEATER
2.1.1 ELECTRONIC CONTROL UNIT (1)
The control unit SG 1553 in 12 volt and 24 volt versions
is the central component to ensure controlled operation
and monitoring of combustion.
Figure 1: Control Unit
2.1.2 OVERHEAT FUSE (15)
The overheat fuse protects the heater from too high and
inadmissible temperatures. The overheat fuse contains a
fusible link that reacts when the temperature exceeds
138° C (280° F), and switches the heater off with a purge
cycle.
Figure 2: Overheat Fuse
2.1.3 TEMPERATURE LIMITER (17)
The temperature limiter is a thermostat that responds
(opens) at a temperature of 95° C (203° F). The
temperature limiter will automatically reset (closes) once
temperature falls well below 95° C (203° F). Once the
limiter has reset, the heater will have to be switched off
and back on to restore operation.
Figure 3: Temperature Limiter
2.1.4 TEMPERATURE CONTROL THERMOSTAT (16)
After the operating temperature has been reached, the
temperature control thermostat opens and shuts off the
heating cycle and a purge cycle begins. Once the
operating temperature drops to the lower temperature
threshold of the control thermostat, the thermostat
closes and another heating cycle begins, thus,
maintaining a consistent coolant temperature.
Figure 4: Temperature Control Thermostat
NOTE: DBW 2020/300 Only. An optional
control thermostat could be mounted in the
heating system in place of the control
thermostat located on the heater.
Control unit
Overheat Fuse (white wires)
Response temperature
138° C (280° F)
Temperature Limiter (green wires)
Switching temperature
– opens at 95° C (203° F)
Temperature Control Thermostat
Version 1 (red and green wires)
– opens at 75 ± 3° C (167 ± 6° F)
– closes at 68 ± 5° C (154 ± 9° F)
Version 2 (orange and white wires)
– opens at 70 ± 3° C (158 ± 6° F)
– closes at 60 ± 5° C (140 ± 9° F)
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