Table of Contents
Advertisement
Sec. 7
Page 108
GM COACH MAINTENANCE MANUAL
WIRING AND MISC. ELEC.
continuity, using a voltmeter or a test light having
a 12-volt, 1.5 candlepower bulb, as follows:
2. Control switch must be in "RUN" position
and emergency door unlatched. With one test lead
grounded, touch other lead to each buzzer termi-
nal.
If
no current is obtained at either terminal,
defective wiring between control panel and buzzer
is indicated.
3.
If
current is indicated at one terminal,
ground the dead terminal with a jumper wire.
Buzzer should sound.
If
buzzer fails to sound,
remove buzzer for repair or replacement.
4. To check for defective rectifier, connect
jumper lead from number 6 rectifier junction ter-
minal to buzzer terminal (next to rectifier).
If
buzzer sounds, rectifier is defective and must be
replaced.
5. To test circuit (except buzzer and recti-
fier),
connect voltmeter or test light leads to
rectifier junction terminals as follows:
1 and 3,
2 and 3, 5 and 3, 6 and 3. (Engine must be stopped,
emergency door unlatched, and control switch in
"RUN" position when making these tests.)
If
cur-
rent is not obtained in one or more of these tests,
refer to "Alarm and Signal Wiring Diagram" to
determine which circuit is defective.
6.
If
current indication is not obtained, switch-
es and wiring should be carefully checked for open
circuit.
ALARM SYSTEM RECTIFIER
Rectifier, mounted on driver's compartment
trim panel ahead of steering column, is connected
in series between the tell-tale lights and the alarm
buzzer (refer to "Alarm and Signal Wiring Dia-
gram" in back of manual). Rectifier permits cur-
rent flow in one direction only, thus preventing
more than one tell-tale light from illuminating
when only one abnormal condition exists. Rectifier
requires no maintenance other than making sure
that leads are securely soldered to terminals. To
test for defective rectifier, accomplish step 4 un-
der "Buzzer Maintenance."
Adjusting
Screw
Contacts
Bi-Metal Element
Heating
Element
Figure 6-Moto-Gord Unit
TP 3402
ALARM SWITCHES
The audible alarm system is controlled by
four switches, each of which controls an electrical
circuit.
These four circuits are:
(1) Low Oil
Pressure, (2) Water Overheat, (3) Low Air Pres-
sure, and (4) Emergency Door Open.
Whenever any of these conditions exist, the
switch controlling that circuit is closed, completing
the circuit to tell-tale and alarm buzzer. These
circuits, on standard vehicle, are operative only
when engine control switch is in run position. Re-
fer to "Alarm and Signal Wiring Diagram" in back
of manual for electrical circuits.
Maintenance,
tests,
and
location
of
these
switches are described in other sections of this
manual as previously indicated under "Index of
Electrical Units."
MOTO-GARD
Air-operated injector shut-off system, which
automatically stops engine when control switch is
placed in off position, is used as special equip-
ment on some vehicles. Operation and maintenance
of this system is explained in ENGINE (SEC. 8).
Moto-Gard system is used in conjunction with
the air injector shut-off system· on some installa-
tions. Moto-Gard system comprises the Moto-Gard
unit, which is a thermal type switch, a rectifier,
and a relay, all mounted on engine compartment
control panel. These units are interconnected with
the water overheat and low oil tell-tale alarm
system and the air injector shut-off magnet valve
as shown on special wiring diagram in back of
manual, Operation of system follows:
Relay and Moto-Gard unit are both connected
to "RUN" side of Diesel control switch.
Relay
points are normally closed, thus magnet valve is
always energized with control switch in "RUN"
position, and air pressure is exhausted from in-
jector shut-off air cylinder. When engine over-
heat thermostat or low oil pressure switch con-
tacts close, circuit is completed through Moto-
Gard heating element (fig. 6).
Heat created in
heating element causes bi-metal contact arm to
bend, closing contacts. This completes circuit
through relay winding, causing relay points to open
and interrupt circuit to injector shut-off magnet
valve. With magnet valve de-energized, air pres-
sure is admitted to injector shut-off air cylinder,
and injector racks are moved to no-fuel position.
Action of Moto-Gard is not immediate, as it
requires 25 to 35 seconds for the unit to heat up
sufficiently to close the contacts.
Purpose of
rectifier used with this system is to prevent back
feed of current from causing the system to func-
tion when the overheat thermostat or low oil pres-
sure switch contacts are open.
Advertisement
Table of Contents
