GMC 4000 Series Service Manual page 429

Sec. 6Y
Page 418
A/C GENERATING SYSTEM
Figure 13— Adjusting Voltage Setting
(Two-Unit Type Regulator) (Typical)
c. Return variable resistor to the closed or
"no resistance" position.
d. Bring engine speed up to approximately
2500 rpm and note the voltage setting. Refer to
applicable "Temperature Voltage Chart" in "Speci­
fications" at end of this section.
NOTE: The regulator unit should be operating
on the upper or shorting contacts. If it will not
operate on the upper contacts, the battery is in
extreme state of discharge, and must be at least
partially recharged before proceeding with test.
6. To prevent accidental grounding and con­
sequent damage to internal regulator parts when
removing or installing regulator cover, perform
the following steps in order listed:
a. Disconnect #4 lead at harness connector.
b. Disconnect jumper lead at generator "BAT"
terminal.
c. Remove regulator cover.
d. Reconnect jumper lead to generator "BAT"
terminal.
e. Connect #4 lead to harness connector.
7. To adjust the voltage setting, turn adjusting
screw as shown in figure 13.
IMPORTANT: Always turn screw clockwise to
make final setting to insure spring-holder being
against head of adjusting screw. If necessary, pry
holder up against screw head before turning screw
clockwise.
8. After making the setting, cycle the gener­
ator again as directed previously in Step 5.
9. Operate engine at approximately 2500 rpm
and note voltage setting. Readjust if necessary.
10. Check the voltage setting while operating
on the lower set of contacts as follows:
Slowly increase the resistance of the variable
resistor with the engine operating at 2500 rpm
until the regulator begins to operate on lower set
of contacts. Then, note the change in voltage read­
ing. The upper set voltage should be 0.1 to 0.4
G M C S E R V I C E M A N U A L
A d ju stin g Screw
(Turn To A d just
V o lt a g e Setting)
volts higher than on lower contacts.
The most desirable method for determining
that the regulator is operating on the lower set of
contacts when the cover is installed is to use ear­
phones (if available) connected across the regulator
"F" terminal to ground. As the variable resistor
is turned, and operation changes from the upper set
of contacts to the lower set, the earphones sound
will fade away and stop completely and then return
when the lower set of contacts begin to operate.
The alternate method is visual observation, but
this is le ss desirable because the cover must be
removed which affects temperature stabilization.
NOTE: If turning the variable resistor does
not cause the regulator to operate on the lower set
of contacts, return the variable resistor to the "no
resistance" position, turn the carbon pile to slight­
ly load the battery, and then adjust the variable
resistor to cause the regulator to operate on the
lower set of contacts. Usually, turning on the ve­
hicle head lights can substitute for the carbon pile.
The difference in voltage between the oper­
ation of the upper set of contacts and the lower
set is increased by slightly increasing the air gap
between the armature and center of core and de­
creased by slightly decreasing the air gap using
nylon adjusting nut. This adjustment can be made
while the regulator is operating. If necessary to
make this air gap adjustment, recheck the voltage
setting of both sets of contacts.
11. Always make final voltage test after the
regulator cover is installed.
IMPORTANT: Observe special procedure in
Step 6 previously when installing and removing
regulator cover.
12. The regulator can be removed and checked
as directed later under applicable "Voltage Regu­
lator."
SYSTEM WITH 1116374 OR
1116378 REGULATOR
NOTE: On vehicles equipped with the 1116374
regulator, No. 2 terminal on regulator is energized
by system voltage rather than by generator "R"
terminal voltage.
1. Make connections as shown in View A, fig­
ure 14.
CAUTION: DO
lead connected longer than five minutes.
2. If voltage in Step 1 is less than 0.9 volt or
greater than 2.0 volts, repair or replace the reg­
ulator.
3. If voltage in Step 1 was between 0.9 and 2.0
volts, proceed as follows:
a. Make connections as shown in View B, Part
1, figure 14, and record the voltage drop.
NOTE: Voltmeter is connected between battery
NOT leave jumper