Generac Power Systems 53187 - Manual (Page 121)

PARTS
ENGINE ELECTRICAL SYSTEM SECTION 5.5
ENGINE PROTECTIVE SYSTEMS
Section 5.5
ENGINE PROTECTIVE DEVICES
General
The engine w ill shut dow n autom atically in the
event of any one or m ore of the follow ing occurences:
□ Low oil pressure.
□ High engine coolant tem perature.
□ Engine overspeed.
System Operation
The engine m ounts both a low oil pressure sw itch
and a high coolant tem perature sw itch. Both sw itches
are connected to Term inal 12 of the engine control
circuit board, via W ire 85. Either a low oil pressure
condition or a high coolant tem perature condition w ill
cause W ire 85 and Term inal 12 to be connected to
fram e ground. Circuit board action w ill then Initiate
engine shutdow n.
AC frequency signals are delivered to the engine
control circuit board Term inals 5 and 6, via W ires 11
and 22. Should frequency exceed approxim ately 69*71
Hertz (2070-2130 rfjm ), an engine shutdow n w ill occur
after about four (4) seconds.
Low Oil Pressure Switch
DESCRIPTION:
The sw itch is norm ally-closed, but is held open by
engine oil pressure during cranking and running.
Sw itch contacts closure w ill occur w hen oil pressure
drops below approxim ately 10-11 psi.
TESTING THE SW ITCH:
W ith engine shut dow n, disconnect W ire 85 from
the sw itch term inal. Set a VOM to Its "Rxl“ scale and
zero the m eter. Connect one VOM test probe to the
sw itch term inal, the other test probe to a clean fram e
ground. The VOM needle indicate "continuity*.
Now , start the engine. Again, connect the VOM test
probes across the sw itch term inal and ground. The
m eter should read "infinity".
W ith the engine runnino at no-load condition, con­
nect the term inal end of W ire 85 to a clean fram e
ground. The engine should shut dow n.
High Coolant Temperature Switch
DESCRIPTION:
This norm ally-open therm ostatic sw itch has a
sensing tip w hich Is im m ersed in engine coolant.
Should coolant tem perature exceed approxim ately
245*-266‘ F. the sw itch contacts w ill close to
ground Term inal 12 of the circuit board. Circuit board
action w ill then effect an engine shutdow n.
TESTING THE SW ITCH:
To test the high coolant tem perature sw itch, pro­
ceed as follow s:
Figure 1. Low O il Pressure Sw itch
Figure 2. High Coolant Tem perature Sw itch
1. W ith Sw itch Installed: W ith engine shut dow n,
disconnect w ire from sw itch term inal. Connect a VOM
to the sw itch term inal and to fram e ground. The m eter
should read "infinity". Any reading other than "infinity"
is cause for sw itch replacem ent.
2. Testing w ith Sw itch Rem oved: Disconnect W ire
85, rem ove the sw itch and test as follow is (see Figure
3):
a. Im m erse the sw itch In a 50-50 m ixture of ethylene
glycol base anti-freeze and w ater as show n.
b. Set a VOM to its "Rxl “ scale and zero the m eter.
c. Connect one VOM test probe to the sw itch w ire
term inal, the other test probe to the sw itch body. The
m eter should read "infinity".
d. Place an accurate therm om eter into the fluid m ix­
ture.
e. Heat the fluid. At approxim ately 245*-266' F., the
sw itch contacts should close anf the m eter should
read "continuity".
f. W ith m eter still connected, allow fluid to cool.
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