Guardian 4721, Repair Manual

Page: 88 / 115

3. Install battery cables, making sure all cable
clamps are tight. The red battery cable (from
control contactor (CC) must be securely
attached to the positive (+) battery post; the
black cable (from the frame ground stud) must
be tightly attached to the negative (-) battery
post.
B.Test Battery State of Charge:
1. Use an automotive type battery hydrometer to
test battery state of charge.
2. Follow the hydrometer manufacturer's instruc-
tions carefully. Read the specific gravity of the
electrolyte fluid in all battery cells.
3. If the hydrometer does not have a "percentage
of charge" scale, compare the reading obtained
to the following:
a. An average reading of 1.260 indicates the
battery is 100% charged.
b. An average reading of 1.230 means the
battery is 75% charged.
c. An average reading of 1.200 means the
battery is 50% charged.
d. An average reading of 1.170 indicates the
battery is 25% charged.
C.Test Battery Condition:
1. If the difference between the highest and lowest
reading cells is greater than 0.050 (50 points),
battery condition has deteriorated and the bat-
tery should be replaced.
2. However, if the highest reading cell has a spe-
cific gravity of less than 1.230, the test for condi-
tion is questionable. Recharge the battery to a
100 percent state of charge, then repeat the test
for condition.
RESULTS:
1. Remove the battery and recharge with an automotive bat-
tery charger, if necessary.
2. If battery condition is bad, replace the battery with a
new one.
TEST 7- TEST CONTROL CONTACTOR CC
DISCUSSION:
During any startup, control board action delivers 12
volts DC to the coil of a control contactor. The control
contactor energizes, its contacts close, and battery
power is delivered to the starter motor (SM) to crank
the engine. A defective control contactor (CC) can
prevent the engine from being cranked in both the
automatic and manual modes of operation.
PROCEDURE:
Use a DC voltmeter (or VOM) to test control contactor
(CC) operation, as follows:
1. Connect the positive (+) test lead to the control contac-
tor’s Wire 56 terminal, the common (-) test lead to a clean
frame ground.
2. Set the AUTO-OFF-MANUAL switch to MANUAL. The
meter should indicate battery voltage (about 12 volts DC).
RESULTS:
1. If battery voltage is not indicated, go to Step 3.
2. If battery voltage is indicated but engine does not crank,
go to Step 4.
3. Connect the meter test leads across terminals 0 and 56
of terminal board TB1 (in the control console). Set the
AUTO-OFF-MANUAL switch to MANUAL. The meter
should read battery voltage.
Figure 4. Control Contactor Test Points
RESULTS:
1. If battery voltage is indicated in Step 3 but not in Step 2,
Wire 56 between the control contactor and terminal board
TS1 is open. Repair, reconnect or replace Wire 56 as
necessary.
2. If battery voltage is not indicated in either Step 2 or Step
3, replace the control board.
3. If battery voltage is indicated in both Steps 2 and 3, but
the engine does not crank, go on to Step 4.
4. Connect the meter test leads across the large terminal
stud on the control contactor to which the battery cable
(Wire 13) attaches and frame ground. The meter should
read battery voltage.
5. Now, connect the positive (+) meter test lead to the
starter motor (SM) terminal stud and the common (-) test
RED
13
13
56
0
16
PART 4
Page 84
DC CONTROL
LIQUID COOLED
ENGINE UNITS
SECTION 4.4
DIAGNOSTIC TESTS