Operating instructions

4.6.3 Sleeper and Engine Block Heating
A: Parallel Plumbing Circuits
Fig. 408: Parallel Plumbing Circuit
Parallel plumbing circuits:
Vehicles equipped with heating/air conditioning units and normally closed solenoid coolant shut-off
valves require an additional relay and circuitry to overide the solenoid valve whenever the Webasto
heater is in operation.
This modification is necessary to ensure coolant circulation during Webasto heater operation.
408
4 Installation Thermo 90 S