A main engine on your fishing trawler has experienced a low coolant water level alarm even though the water level in the expansion tank is normal. Assuming that the float activated switch is designed to open at low coolant level to activate the alarm, which of the following would account for this?
• Float switch logic – understand what it means when a switch is designed to open to activate an alarm • Difference between open circuit (no continuity) and closed circuit (continuity) in alarm wiring • How mechanical sticking vs electrical connection problems would affect whether the alarm sees the circuit as open or closed
• At normal coolant level, should the float switch contacts be open or closed in this design? What does that imply about current flow? • If the alarm is sounding even though the coolant level is normal, what must the alarm circuit be "seeing" – an open or a closed circuit? • For each option, ask: does this condition make the circuit look open or closed to the alarm panel?
• Identify which choices would result in an open circuit (no continuity) in the alarm wiring when level is actually normal • Rule out any option where the circuit would remain permanently closed, because that would usually prevent a low-level alarm from occurring • Check whether a physically stuck float (not moving) would cause a false low-level alarm or the opposite problem: no alarm when low level actually occurs
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