MCi Crusader II 1989 Maintenance Manual page 222

Date
1-1-89.
Page·_. __
7 _- 2 _ _ _
MC-9 MAINTENANCE MANUAL
The evaporator motor circuit breaker is 80 amp. The evaporator
motor circuit breaker is also a manual reset type. ·
Smaller circuit breakers of the self-resetting type are located
in an external junction panel at the left hand front below driver's
window and in a panel at the left hand rear engine compartment
wall. When one ol these circuit breakers opens due to a shorted
circuit. it will automatically reset itself when the breaker element
cools. As long as the short exists. the breaker will continue to
open and close intermittently. In this case, turn the defective
circuit off until the cause can be located and corrected.
The circuit breaker box tor optional in-station lighting is
mounted to the rear wall of the left hand front service
compartment. See figure
7-3.
RELAYS
Relays are used to automatically energize or de-energize a
circuit from a remote location. The relay draws a very low
current to energize ,ts coil. Once the coil is energized. it devel-
ops a magnetic field which will pull a switch arm closed or open
to either energize or de-energize a given component. Because
the control current required for the coil is very low, the relay
allows a remote station (e.g. driver's switch panel) to control a
high energy circuit without running great lengths of costly high
capacity cable. With the use of a relay. the need for high amper-
age switches and heavy connectors is eliminated.
Figure 7-4. Alternator.
The MC-9 uses control relays for the Low and High Note
Horns. Headlamps, Discharge and Blower cut-ins. Engine
Stop, Stop Lights, Turn Lights, Reverse Solenoids. Starter
Solenoid, Condenser and Evaporator Motor, Temp. & Level
Sensors. Driver's Defroster. Step-Down Lamps at aisle,
Alternator Field, and Heat Control Box.
NOTE: The relays should have the 5/16"
stud nuts tightened to 50=-. 10 in. lbs. (5.6..::.
Nm) torque.
GEAR ORIVEN ALTERNATOR - OIL COOLED
The gear driven.
011
cooled alternator (figure 7-4) is a brush-
less. self-rectifying unit. in which all current carrying members.
windings. diodes. and field coils are stationary. The only moving
component is the rotor. ·
The oil-cooled alternator is a totally enclosed unit. cooled
and lubricated by engine oil. The oil inlet is on the diode end
cover. the oil drams back into the engine crankcase internally
or through the drive end frame. drive adapter housing and the
oil drain tube. The alternator should never be operated with the
oil supply line disconnected. A continuous flow ol engine oit
flows through the alternator to lubricate the bearings and cool
the assembly.
A relay or "R" terminal is tapped to energize a control relay in
the electrical system.
CAUTION: The alternator is designed for
use only on a negative ground system. If a
positive ground battery is connected to the
alternator, the alternator and wiring har-
ness will be instantly destroyed. Always
ensure that the alternator and batteries are
negative ground. The alternator will not
reverse to accept inverse polarity. Also, do
not ground or short across any of the alter-
nator or regulator terminals.
There are three components in the alternator which require
electrical checks; the field winding, the six diodes. and the
stator winding. See figure
7-5.
CAUTION: Before checking the alternator,
turn off the battery disconnect switch.
FIELD WINDING - The field winding may be checked for shorts
and opens with an ohmmeter. To check the field winding, con-
nect the ohmmeter from the field terminal to ground. The normal
resistance value is
3.0
to
3.3
ohms at
80°F. (27° C.).
A resistance
reading above normal indicates an open. and a reading less
than normal indicates a short.
An alternate method of checking is to place a battery of
specified voltage. and an ammeter in series with the field wind-
ing. The current should .register 7.2 to 8.3 amperes at 24 volts.
A defective field can be replaced by removing the end frame
on which the field terminal is located and then removing the
four field coil mounting screws. See the section entitled Disas-
sembly tor a detailed procedure.
2
R
Figure
7-5.
Alternator Wiring Diagram (Typical).