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© 1997 Whirlpool Corporation
Cooking Products Service Manual
Original March 1997 4322167
Page 1-1
THEORY OF OPERATION
The microwave oven is powered by the 120-
volt line. Whenever the door is closed and a
cooking function is programmed through the
control panel’s keypad, relay contacts on the
control board close, and complete a circuit
from the L1 side to the neutral side of the line.
The control board uses five relays to operate
the various functions of the microwave oven
(see below). The relays are controlled by the
microcomputer on the control board, and per-
form the functions shown below.
Relay 4 controls the speed of the blower motor
through the contol panel. The base thermal
fuse will also turn the blower motor on to its
low speed if the temperature reaches 133˚F.
The schematic configuration for relay 4 is
shown in the following diagram. The relay is
explained in further detail on the following
page.
RELAY 4
BASE
THERMAL
FUSE
(LOW)
(HI)
(C)
(C)
(NC)
(NO)
BLOWER
MOTOR
L1
Relay 1 ........................................................ Oven Light/Fan & Stirrer Motors
Relay 2 ........................................................ High Voltage Section
Relay 3 ........................................................ Low-Speed Blower Motor
Relay 4 (N.C. Contacts) ........................... Auto Low-Speed Blower Motor
Relay 4 (N.O. Contacts) ........................... High-Speed Blower Motor
Relay 5 ........................................................ Turntable Motor
CN3
RELAY RY2
MICROCOMPUTER
RELAY RY5
RELAY RY4
RELAY RY3
CONTROL
CIRCUIT
BOARD
RELAY RY1