Operating instructions

1. The Thermo 90 S is switched off.
2. Time has elapsed on the timer.
3. The vehicle battery voltage drops below 10.5V (20.5V).
4. The Thermo 90 S runs out of fuel.
5. A fault lock out occurs, indicated by a coded flashing signal on the operating indicator light during
the after run cycle of the heater or if equipped with a model 1531 7-Day Digital Comfort Timer a
fault code number (i.e. 07) will be displayed in the timer window until the fault is cleared.
(refer to Troubleshooting section of this manual for further information).
2.2 Switching Off
When heating is no longer required, switch the Thermo 90 S heater off. The indicator light turns off,
combustion extinguishes followed by an after run cycle of approximately 90 seconds.
2.3 Engine Preheating
1. Set the timer 30 min. to 1 hr. before you want to start engine. The heater will start up at set time.
(See timer operating instructions.)
Or switch the toggle switch or “instant on” switch on your timer in the vehicle dash to “ON”.
The heater will start up.
2. When the run time has elapsed on your timer the Thermo 90 S will automatically shut down.
Or, when engine preheat is no longer required, switch the Thermo 90 S heater “OFF”.
The Thermo 90 S will go through the after-run cycle.
2.4 Engine and Sleeper Heating
1. Switch the toggle switch (or the “instant on” button of the timer) in the vehicle dash to “ON”.
The heater will start up if coolant temperature is below 167°F (75°C). Above this temperature only
the coolant circulation pump will run until coolant temperature drops below 167°F (75°C).
2. Switch on the thermostat and set to desired comfort range. The fan will cycle “ON” and “OFF” and
maintain selected comfort range.
3. When engine and sleeper heating is no longer required, switch the Thermo 90 S “OFF”.
The Thermo 90 S will go through the after-run cycle.
2.5 Operation with Digital Timer Models 1529 & 1531
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2 Operating the Webasto Thermo 90 S Thermo 90 S
NOTE
Continuous fan operation over extended periods will run down the vehicles batteries.
NOTE
To reduce battery discharge, turn off unnecessary equipment, i.e. radio, position lights, etc.
NOTE
Different blower interlock harnesses are available, check with your Webasto distributor/dealer for
options and application.