Engine Protective Devices; Low Oil Pressure Switch; High Coolant Temperature Switch; Overspeed Protection - Guardian 4270 Diagnostic Repair Manual

Section 5
ENGINE DC CONTROL SYSTEM
SHEATH
ASBESTOS
HEAT-WIRE
MAGNESIUM
OXIDE
POWDER
Figure 5-11. – Glow Plug

ENGINE PROTECTIVE DEVICES

The engine will shut down automatically in the event
of anyone or more of the following occurrences:
• Low oil
• High engine coolant temperature
• Engine overspeed

LOW OIL PRESSURE SWITCH

The oil pressure switch has normally-closed contacts.
When the engine is cranking or running, oil will pass
through the switch, which opens the contacts. If oil
pressure should drop below 10 PSI, the contacts will
close to ground sending a signal to the printed circuit
board to shut unit down on wire 85.
LOW OIL
PRESSURE
SWITCH
Figure 5-12. – Low Oil Pressure Switch
Page 28
BODY
NUT
INSULATING
BUSHING
CENTER
ELECTRODE
ADAPTER

HIGH COOLANT TEMPERATURE SWITCH

The high coolant temperature switch has normally
open contacts. This switch is immersed in engine
coolant. If the coolant temperature should exceed
245-266 degrees F, the switches contacts will close
to ground, sending a signal to the printed circuit board
to shut down the unit via wire 85.
Figure 5-13. – High Coolant Temperature Switch

OVERSPEED PROTECTION

Generator A/C frequency signals are delivered to
Terminals 5 and 6 of the engine control circuit board
via wires 22 and 44. Should engine/generator speed
exceed 69 to 71 Hertz for longer than 4 seconds, the
circuit board will cause an engine shutdown.