GMC 4000 Series Service Manual page 427

Sec. 6Y
Page 416
A/C GENERATING SYSTEM
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W IR IN G H A R N E S S
C O N N E C T O R A T R E G U L A T O R
Figure 8 — Generator Output Test— Jum per Lead
Connection at Regulator (Typical)
output terminal and "NEG" voltmeter lead to ground
on chassis.
2. Start engine and turn heater motor to med­
ium speed position.
3. Increase engine speed until voltmeter read­
ing does not increase and record the reading.
CAUTION: DO NOT exceed 2000 rpm.
4. Disconnect ground (NEG.) cable from bat­
tery.
5. If voltmeter reading is lower than in Step
3. above, a defective generator is indicated. Re­
move generator and repair.
GENERATOR OUTPUT TEST
1. Disconnect positive cable from battery.
2. Remove wire from "BAT" terminal on gen­
erator, and connect an ammeter between wire and
"BAT" terminal on generator (fig. 7).
3. Install a voltmeter between the generator
"BAT" terminal and "GRD" terminal.
4. Pull latch on regulator upward to disengage
from connector, then pull wiring harness connec­
tor from regulator. Connect a jumper leadbetween
"F" terminal socket and #3 socket as shown in
figure 8.
IMPORTANT: With wiring connected as shown
in figure 7, the voltage regulator is taken out of
the circuit, and causes field to be energized by full
battery voltage. Generator output voltage must be
controlled by loading the battery with a carbon
pile or turning on vehicle a ccessories. Do not per­
mit voltage to exceed setting specified for regu­
lator as listed in "Specifications."
5. Connect a tachometer to engine, then con-
G M C S E R V I C E M A N U A L
4
T-641-1
nect positive cable to battery and start engine.
Adjust engine speed and carbon pile (if used) or
with vehicle a ccessories to provide rated voltage.
Ratings for each generator are given in "Specifi­
cations" at end of this section. If generator does
not produce current within its rated capacity, it
can be considered defective and in need of repair.
connect wiring harness connector to regulator.
going tests, yet the battery remains undercharged,
adjust voltage regulator setting as explained under
applicable regulator later in this section.
charge, the regulator field relay or possibly the
generator is at fault. To determine which is at
fault, proceed as follows:
nector term inals as shown in figure 9.
Observe the voltmeter reading. If reading is 5
volts or over and indicator shows no charge, the
field relay is defective and must be checked.
trouble is in generator. Refer to applicable "Gen­
checked on the vehicle as follows:
up of test equipment.
Figure 9 — Testing Regulator Field Relay
(Two-Unit Type Regulator)
6. Remove instruments and jumper lead and
7. If no defects were discovered by the fore­
REGULATOR UNIT FIELD RELAY
TEST O N VEHICLE
If the generator charge indicator shows no
1. Make connections to the regulator and con­
2. Start engine and operate at fast idle speed.
3. If voltmeter reading is below 5 volts on
regulator 1119515, or 8 volts on regulator 1119507,
erator" section explained later.
4. The field relay closing voltage can be
NOTE: Refer to figure 10 which shows hook­