Generac Power Systems NP-40G - Manual (Page 96)

Section 6.5- ENGINE PROTECTIVE DEVICES
General
The engine mounts an Oil Pressure Switch (LOP)
and an Oil Temperature Switch (НТО). These two
switches, In conjunction with the^gine Controller
circuit board, protect the engine against (a) low oil
pressure and (b) high oil temperature.
The engine protective circuit is shown In Rgure
1 .
Oil Pressure Switch
DESCRIPTION:
The Oil Pressure Switch has normally-closed
contacts which are held open by engine oil
pressure during cranking and running. Should oil
pressure drop below approximately 5 psi, the
switch contacts will dose to complete the Wire 85
circuit to ground. Engine Controller circuit board
action will then de-energize the Wire 14 circuit and
the engine will shut down.
The Engine Controller circuit board provides a
time delay to allow oil pressure to build during
startup, to prevent premature shutdown.
NOTE: Early production NP40G units wore
equipped with a Low Oil Switch rated 10 psi (Part
No. ¿0108). Later production units are now
equipped with a Low Oii Switch rated 5 psi (Part No.
Т/бЕЛ. Units equipped with the 10psi Switch must
be retrofitted with the new 5 psi Switch (Part No.
77667). .
TESTING THE SWITCH:
Use a voit-ohm-milliammeter (VOM) to test the oil
pressure switch. Connect the VOM test leads
across the switch terminal and the switch body.
With the engine shut down, the meter should read
“continuity” (a very small resistance is
acceptable). With engine running, the meter should
read “infinity”.
Oil Temperature Switch
DESCRIPTION:
This thermostatic switch has normally-open
contacts. Should engine oil temperature exceed a
preset safe value (about 293^ F.), the switch
contacts will close. On closure of the Switch
contacts, the Wire 85 circuit will be connected to
frame ground. Engine shutdown will then occur.
NOTE: Eariy production NP40G units were
equipped with an Oil Temperature Switch rated
265^ F. That Oil Temperature Switch has been
replaced on later production units by the 293^ F.
Switch (Part No. 94090). Early units having the
26S^ F. Switch may be subject to overtemperature
shutdown and should be retrofitted with the new
293« F. Switch.
Figure 1. Engine Protective Circuit
BCCB - BtraiNB CONTROL CIRCUIT BORRO
НТО ■ HIOH Olb TSHP. SWITCH
LOP ■ LOW OIL PRBSSURB SWITCH
ECCB
T
НТО
LOP
O-p-o—< I
’A
^
A. Schematic
Page 6.5-1