Section 2.4 - Diagnostic Tests; Introduction; Safety; Ac Troubleshooting - Generac Power Systems 7 kW NG Repair Manual

AC GENERATORS

INTRODUCTION

This section familiarizes the service technician with acceptable
procedure for the testing and evaluation of various problems
that can occur on the standby generators with air-cooled
engines. Use this section in conjunction with Section 2.3,
"Troubleshooting Flow Charts." The numbered tests in this
section correspond with those of Section 2.3.
Some test procedures in this section may require the use of
specialized test equipment, meters or tools. Most tests can be
performed with an inexpensive Volt-Ohm-Milliammeter (VOM).
An AC frequency meter is required where frequency readings
must be taken. To measure AC loads it is acceptable to use a
clamp-on ammeter.
Testing and troubleshooting methods covered in this section
are not exhaustive. No attempt has been made to discuss,
evaluate and advise the home standby service trade of all
conceivable ways in which service and trouble diagnosis must
be performed. Accordingly, anyone who uses a test method
not recommended herein must first satisfy himself that the
procedure or method he has selected will jeopardize neither his
nor the products safety.

SAFETY

Service personnel who work on this equipment should be
aware of the dangers of such equipment. Extremely high and
dangerous voltages are present that can kill or cause serious
injury. Gaseous fuels are highly explosive and can ignite by the
slightest spark. Engine exhaust gases contain deadly carbon
monoxide gas that can cause unconsciousness or even death.
Contact with moving parts can cause serious injury. The list of
hazards is seemingly endless.
When working on this equipment, use common sense and
remain alert at all times. Never work on this equipment while
you are physically or mentally fatigued. If you do not understand
a component, device or system, do not work on it.

AC TROUBLESHOOTING

It is always good practice to continue to ask questions during
the troubleshooting process. When evaluating the problem
asking some of these questions may help identify the problem
quicker.
• What is the generator supposed to do?
• What fault (Alarm) is shutting the generator down?
• Is the fault a symptom of another problem?
• Does the generator have the same fault consistently?
• When does the fault occur?
• After the fault occurred what was displayed in the LCD?
• Why would this happen?
• How would this happen?
• What type of test will either prove or disprove the cause of
the fault?
PART 2
TEST 1 – CHECK AC OUTPUT VOLTAGE
Discussion
Use a Volt-Ohm-Milliammeter (VOM) to check the Generators
output voltage. Test output voltages at the unit's main circuit
breaker (MLCB) terminals. Refer to the unit's Data Plate for
rated line-to-line and line-to-neutral voltages.

Use extreme caution during this test. The Generator
will be running. High and dangerous voltages will
be present at the test terminals. Connect meter
test clamps to the high voltage terminals while the
Generator is shut down. Stay clear of power terminals
during the test. Make sure the meter clamps are
securely attached and will not shake loose.
Procedure
1. Set the Volt-Ohm-Milliammeter (VOM) to measure AC
voltage.
2. With the engine shut down, connect the meter test leads
across the load terminals of the Generators MLCB. This
will measure line-to-line voltage. See Figure 46.
LINE
TEST POINT
TEST POINT
Figure 46. Test 2 Test Points
3. Set the MLCB to the "Open" position. Ensure that all
electrical loads are disconnected from the Generator.
4. Set the AUTO-OFF-MANUAL switch to the MANUAL
position.
Note: AC under and over-voltage shut downs have a 10
second delay.
5. Set the MLCB to the "Closed" position. Measure and
record the voltage.
6. Set the AUTO-OFF-MANUAL switch to the OFF position.
Results
1. If the VOM indicated approximately 240-244 VAC, the
output voltage is good.
Section 2.4
Diagnostic Tests
LOAD
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