Operating instructions

2. Operating the Webasto Thermo 90 S
Before switching on the Thermo 90 S, set vehicle heating system to the “heat” position and open any
shut off valves. Depending on the type of control installed in the dashboard of the vehicle, the
Thermo 90 S can be operated by the following methods.
2.1 Switching On
Using a timer: Using a switch:
Timer Switch
Pushing the “instant heat” button lights the “operation indicator” on the timer.
Or
When the switch is used for turning “ON” the Thermo 90 S, the operation indicator (toggle) lights up.
The coolant circulating pump, ceramic igniter and combustion air fan start operation and after
approximately 50 seconds combustion starts (audible combustion sound). After the coolant
temperature has reached the set point of 176°F (80°C) the Thermo 90 S will automatically adjust its
heat output to a lower operating range (variable heat output). If the temperature of the coolant
continues to rise and climb over 194°F (90°C) at the heater outlet it will cycle off. When the
temperature falls below 167°F (75°C) the heater will restart and repeat the cycle.
The Thermo 90 S will cycle on and off until:
201
Thermo 90 S 2 Operating the Webasto Thermo 90 S
WARNING
Due to the risk of carbon monoxide poisoning and asphyxiation, the heater must not be operated in
enclosed spaces such as garages or workshops without adequate exhaust extraction.
WARNING
Do not operate any Webasto heater in an area where toxic or explosive materials or fumes may be
present. The heater must be switched “OFF” while refueling and at fueling stations.
NOTE
If heater is being switched on while the engine is at operating temperature, only the circulating
pump will run, coolant temperature must fall below 167°F. (75°C.) before heater will start.
NOTE
Restarting the heater during the after-run period is permitted.