Guardian 4389 Repair Manual page 46

SECTION 2.4
DIAGNOSTIC TESTS
PROCEDURE:
With the frequency between 61-62 Hertz, slowly turn
the slotted potentiometer (Figure 11) until line voltage
reads 244-252 volts.
NOTE: You must remove the access panel on top
of the control panel to adjust the voltage regulator.
NOTE: The voltage regulator is housed above the
generator control panel. The regulator maintains a
voltage in direct proportion to frequency at a 2-to-1
ratio. For example, at 62 Hertz, line-to-neutral voltage
will be 124 volts.
Figure 11. Voltage Adjustment Potentiometer
RESULTS:
1. If the frequency and voltage are now good, discontinue
tests.
2. If frequency is now good but voltage is high or low, go to
Problem 1, Test 4.
TEST 14 - CHECK VOLTAGE AND
FREQUENCY UNDER LOAD
DISCUSSION:
It is possible for the generator AC output frequency
and voltage to be good at no-load, but they may drop
excessively when electrical loads are applied. This
condition, in which voltage and frequency drop exces-
sively when loads are applied, can be caused by (a)
overloading the generator, (b) loss of engine power,
or (c) a shorted condition in the stator windings or in
one or more connected loads.
PROCEDURE:
1. Connect an accurate AC frequency meter and an AC
voltmeter across the stator AC power winding leads.
2. Start the engine, let it stabilize and warm-up.
Page 44
PART 2
3. Apply electrical loads to the generator equal to the rated
capacity of the unit.
4. Check the AC frequency and voltage. Frequency should
not drop below approximately 58-59 Hertz. Voltage
should not drop below about 230 volts (plus or minus 2
percent).
RESULTS:
1. If frequency and voltage drop excessively under load, go
to Test 15.
2. If frequency and voltage under load are good, discon-
tinue tests.
TEST 15 - CHECK FOR OVERLOAD
CONDITION
DISCUSSION:
An "overload" condition is one in which the generator
rated wattage/amperage capacity has been exceed-
ed. To test for an overload condition on an installed
unit, the best method is to use an ammeter. See
"Measuring Current" in Section 1.4.
PROCEDURE:
Use a clamp-on ammeter to measure load current draw, with
the generator running and all normal electrical loads turned on.
RESULTS:
1. If the unit is overloaded, reduce loads to the unit's rated
capacity.
2. If unit is not overloaded, but rpm and frequency drop
excessively when loads are applied, go to Test 16.
TEST 16 - CHECK ENGINE CONDITION
DISCUSSION:
If engine speed and frequency drop excessively under load, the
engine may be under-powered. An under-powered engine can
be the result of a dirty air cleaner, loss of engine compression,
faulty carburetor settings, incorrect ignition timing, etc.
PROCEDURE:
For engine testing, troubleshooting and repair pro-
cedures refer to Problem 11 in Section 4.3. For fur-
ther engine repair information refer to the following
manuals:
• P/N 0C1103 - Service and Repair Manual for Single
Cylinder GN Engines.
• P/N 0E2081 - Service Manual for GTV-990/760 V-
Twin OHVI Engines.
AC GENERATORS