MCi Crusader II 1989 Maintenance Manual page 246

Date 1-1-89 Page 7-26
MC-9 MAINTENANCE MANUAL
exceeds 30 volts for a period of time in excess of 0.5 seconds,
the relay will energize, thus opening the contacts and interrupt
ing the alternator field relay. It has a self-holding feature so that
the interruption will continue until the driver shuts off the master
switch and turns it on again. If the high-voltage condition still
exists, the unit will trip again. The driver will be aware of the fact
bec<1use the alternator discharge light will be.turned on at the
drivers instrument panel and in the engine compartment. The
0 5-second time delay will eliminate false tripping because of
momentary transients caused by turn signals. air conditioners.
• or other circuit interruptions. Under normal circumst,1nces this
relay will never be energized: therefore. 1! draws no power from
the coach supply system until an overload condition occurs. If
the alternator discharge light should come on. 1t would indicate
a malfunction in the electncal system which should be cor-
rected by maintenance personnel. The driver should be advised.
however. to cycle the masters witch 1n an attemptto cure the diffi-
cullies in case the high-voltage condition was only momentary.
The 0.5-second time delay provides protection from transients •.
but w,11 still save light bulbs. electric motors and dashboard
instruments from failures due to a high-voltage condition.
2. Low Oil Pressure Switch Interrupt Function - The func-
tion of this element ,s to prevent the low oil pressure switch from
shutting down the engine before oil pressure. can be estab•
l1shed immediately after engine start-up. The interrupt contacts
have 3-amp capabilities and are in the black wires coming out
of the unit These wires should interrupt the low oil pressure
switch circuit and are connected in series with that switch.
Internally the relay that controls this interrupt 1s normally unen-
ergized and the contacts are normally closed. When the starter
I~ energized. so also is the interrupt relay. thus opening the low
oil pressure switch line. The relay remains energized (and thus
the contacts open) for the duration of the cranking cycle and for
1 O seconds thereafter. The relay in this element is energized
only during the cranking cycle and for 10 seconds thereafter. at
which time it returns to the relaxed or unenergized state. The
only time it draws power. therefore. Is during the cranking cycle
and for 10 seconds thereafter. Starting a new cranking. cycle
(initiated prior to the time that the 10-second period from the
first cranking cycle has expired), the time delay will be rearmed
and a new 10-second cycle will begin at the conclusion of the
cranking period.
3. Starter Protector Function - The function of this portion
of the device is to prevent the starter from being activated if the
engine is turning. This element uses the R-1 lead output of the
alternator to sense engme movement. If the engine Is turning.
no matter how slowly. It will prevent the starter from being
engaged: however. it will still allow the override features ot the
starter switch to function. It does not interrupt the override tor
high engine temperatures or low 011 pressure. Neither will it
interrupt the starter cycle ;;.s soon as the engine begins to crank.
The instant the driver releases the starter switch after cranking.
the starter Is prevented from being re-engaged until the engine
comes to a complete halt. This 1s accomplished by a relay with
contact capabilities of 3 amps. This relay remains unenergized
until such time as the master switch is turned on. At that time the
relay is energized. thus allowing the starter switch to supply
power to the starter solenoid relay. It remains energized and
thus the starter circuit completed until such time that the driver
energizes the starter switch and throughout the cranking cycle.
When the starter button is released and the engine is turning,
the relay de-energizes (thus interrupting the starter solenoid
circuit) and remains in this condition as long as the engine is
turning, no matter how fast or how slowly. Thus the starter
mechanism is prevented from being engaged until the engine
comes to a complete stop. Again, under normal operating con-
ditions, the circuit draws no power from the coach, except
momentarily between the time the master switch is energized
and the engine is started.
While the engine Is running should tne starter switch be
engaged. ,t w1II serve to override the high tempernture or low 011
pressure contacts but will not allow the starter solenoid relay to
be activated
The starter protector element of the 3NT24 device ,s con-
nected to
,1
warning light on the driver's instrument panel. This
light. when ,1Ium1nated. tells the dnver that the starter solenoid
relay ,s armed. Under normal operating conditions. the fight
comes on when the master switch is turned on and will remain
. on until engine start-up has been accomplished.
Should the warning light remain 1llum1.nated after the engine
has started. or 1f 1t comes on during coach operation. the driver
is warned of a fault in the system and that the starter solenoid
relay Is armed. A broken A-1 lead or a faulty relay would cause
the ltght to come on. Either of these malfunctions would prevent
a signal being sent to the starter protection element that the
engine
is
turning over. Under certaih operating cond1t1ons.
such as attempting to crest a long grade without engine shut-
down. the driver might press the starter switch. Before pressing
the starter switch the driver should be certain that the warning
light is not illuminated. He must not use the override feature of
the starter switch if the warning light is on.
If
he does so and
the engine is• turning over. serious damage to the starter or
engine flywheel can result.
TESTING OF 3N124 TRIPLE FUNCTION
PROTECTIVE DEVICE
To test the Triple Function Protective Device after it is
installed in the coach. proceed as follows:
1. With the battery disconnect switch in the .. ON" position.
turn the master switch "ON" at the driver's instrument panel. the
"Starter Alert" telltale light at the dash should be lit. This indi-
cates the starter is ;urned and ready.
2. To test the starter protection feature. start the engine and
DO NOT release starter switch (or keyed ignition switch). The
starter should "drop out" almost immediately following engine
start-up and the telltale light should go out.
3. With the engine at idle. release the starter switch and
attempt to re-engage the starter. There should not be any
response.
4. Ground the left-hand "Hot Engine" alarmstatand hold the
starter switch prior_ to engine shutdown. The engine should
continue to run without starter engagement as long as the
starter switch is held in the "ON" position (starter bypass
feature).
CAUTION: 11 the telltale light remains on
following engine start-up, release the starter
switch (or keyed ignition switch) imme-
diately and DO NOT perform step 3. (No
Starter Protection)
5 .To test the Low Oil Pressure Switch interrupt feature ..
ground circuit #60 at the 3-lb. oil sender while the engine 1s
running. The engine will shut down following approximately a
10-second delay.