Guardian 4721 Repair Manual page 72

SECTION 4.2
OPERATIONAL ANALYSIS
• The "engine warm-up timer" will run for approximately 15 seconds. The "minimum run timer" will run for about
13 minutes. Engine cannot be shut down in automatic mode until the "minimum run timer" has finished timing
(prevents shutdown of a cold engine).
• At approximately 30 Hz, engine cranking terminates. The circuit board's run relay (K2), however, remains ener-
gized.
• A DC (battery) voltage is delivered to the transfer switch's transfer relay (TR) coil, via Wire 194. This voltage is
available through the relay coil and back to the circuit board, via Wire 23. However, control board action holds
the Wire 23 circuit open.
• When the "engine warm-up timer" has timed out, control board action closes the Wire 23 circuit to ground. The
transfer relay (TR) energizes, its normally-closed contacts (1 & 7) open; its normally-open contacts (6 & 9)
close.
• With TR normally-open contacts closed, "Standby" source power is available to the main contacts actuating coil
(C), via Wires E1/E2, transfer mechanism terminals B1/B2, limit switches XA1 and XB1, and a bridge rectifier.
Actuating coil (C) energizes.
• When actuating coil (C) energizes, the main current carrying contacts of the transfer mechanism are actuated
to their "Neutral" position ("Load" terminals disconnected from both power supplies). The main contacts will
remain at "Neutral" as long as actuating coil (C) remains energized.
Page 68
CIRCUIT CONDITION- INITIAL TRANSFER TO STANDBY
DC CONTROL
PART 4
LIQUID COOLED
ENGINE UNITS