Guardian 4721, Repair Manual

Page: 96 / 115

2. Turn OFF both the “Utility” and “Standby” power supplies
to the transfer switch using whatever means provided.
3. If necessary, manually actuate the transfer switch main
contacts to their “Utility” position, i.e., “Load” connected to
the “Utility” power supply.
4. Turn ON the “Utility” power supply to the transfer switch.
5. Set the generator’s main line circuit breaker to its ON or
“Closed” position.
6. Set the AUTO-OFF-MANUAL switch to AUTO.
7. Turn OFF the “Utility” power supply to the transfer switch.
a. Engine should crank and start in automatic mode.
b. After the control board’s engine warm-up timer
has timed out, the transfer relay (in transfer
switch) should energize and transfer to
“Standby” should occur.
8. If the engine starts and runs but transfer does NOT occur,
proceed as follows:
a. With the engine running, connect a jumper wire
across Terminal 23 of terminal board TB2 and
Terminal 0 of terminal board TB1.
(1) The transfer relay should energize.
(2) Transfer to “Standby” should occur.
RESULTS:
1. In Step 8, if transfer to “Standby” occurs when the jumper
wire is connected across
Terminal
s 23 and 0, proceed
as follows:
a. Test Wire 23 (between terminal board TB2 and the
control board connector) for an open condition.
b. If Wire 23 is good, replace the control board.
2. In Step 8, if transfer to “Standby” does NOT occur when
the jumper wire is connected, refer to Section 3.3.
TEST 24 - CHECK VOLTAGE AT TERMINAL
LUGS E1 & E2
DISCUSSION:
Transfer to the “Standby” source cannot occur unless
that power supply is available to the transfer switch.
This test will determine if “Standby” power is available
to the transfer switch terminal lugs.
DANGER: PROCEED WITH CAUTION. HIGH
AND DANGEROUS VOLTAGES ARE NOR-
MALLY PRESENT AT THE TRANSFER
SWITCH TERMINAL LUGS. CONTACT WITH
THESE HIGH VOLTAGE TERMINALS WILL
RESULT IN EXTREMELY DANGEROUS AND
POSSIBLY DEADLY ELECTRICAL SHOCK.
PROCEDURE:
1. Start the generator engine manually, let it stabilize and
warm-up.
2. Set the generator’s main line circuit breaker to ON or
“Closed”.
3. Use an AC voltmeter to test generator line-to-line voltage
across transfer switch Terminal Lugs E1 and E2. Normal
rated generator AC output voltage should be indicated.
RESULTS:
1. If normal “Standby” source voltage is indicated, but trans-
fer to “Standby” does not occur, go to Section 3.3.
2. If normal “Standby” source voltage is NOT indicated, refer
to “Troubleshooting Flow Charts” in Section 2.3.
TEST 25 - CHECK VOLTAGE AT TERMINAL
LUGS N1 & N2
DISCUSSION:
Automatic startup of the generator engine will occur if
the voltage delivered to transfer switch Terminal Lugs
N1/N2 is below a preset value.
PROCEDURE:
Use an AC voltmeter to check line-to-line voltage
across Terminal Lugs N1/N2. Normal rated “Utility”
power source voltage should be indicated.
RESULTS:
1. If normal “Utility” voltage is read, but generator startup
and transfer to “Standby” occurs in automatic mode, go to
Test 29.
2. If normal “Utility” voltage is NOT indicated automatic
startup and transfer is a normal condition.
TEST 26 - CHECK VOLTAGE AT CONTROL
BOARD TERMINALS N1A AND N2
DISCUSSION:
“Utility” power source voltage is delivered to control
board Terminals N1 and N2 (Utility 1 and 2), and from
there to the control boardtransformer. The step-down
transformer reduces this sensing voltage. The
reduced sensing voltage is then delivered to the con-
trol board. If, for any reason, the reduced sensing
voltage to the control board is lost, the circuit board
will initiate engine startup and transfer to “Standby”.
This test will determine if “Utility” source voltage is
available to the control board.
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PART 4
Page 92
DC CONTROL
LIQUID COOLED
ENGINE UNITS
SECTION 4.4
DIAGNOSTIC TESTS