Circuit Description

The fuel manager/filter assembly consists of fuel heater, water-in-fuel sensor, and a filter. Filter contains coalescer, the device that combines small droplets of water into larger ones, and filter/separator. A fuel lift pump delivers diesel fuel from tank to fuel filter. As fuel enters filter, fuel passes first through fuel heater. Heater contains a thermostatic switch. Switch opens or closes to turn heater OFF or ON, depending on temperature of fuel. Fuel then passes through filter. Next, fuel flows through water coalescer. Here droplets of water-in-fuel combine into larger drops and fall into water reservoir in filter. When fuel flows from fuel manager/filter assembly to injection pump, fuel is clean and free of water. Solid state water-in-fuel sensor supplies voltage to a probe. When probe touches water, module closes a switch. This completes a circuit to ground to light water-in-fuel light. A time delay circuit in water-in-fuel module grounds lamp briefly to test bulb each time system is turned ON. Fuel heater is operated by a built-in thermostatic switch. When switch is closed, battery voltage is supplied to heater.