MW24-1100 MICROWAVE OVEN
Theory of Operation
3-2
#814888 - Revision A - May, 2009
Door Sensing and Secondary Interlock Switches
The secondary interlock switch is mounted in the lower
position of the latch hook and the door sensing switch
in the secondary interlock system is mounted in the
upper position of the latch hook (See Figure 3-1). They
are activated by the latch heads on the door. When the
door is opened, the switches interrupt the power to all
high voltage components. A cook cycle cannot take
place until the door is firmly closed thereby activating
both interlock switches. The secondary interlock system
consists of the door sensing switch and secondary
interlock relay located on the control circuit board.
Monitor Switch
The monitor switch is mounted just above the second-
ary interlock switch on the latch hook (See Figure 3-1).
The monitor switch is activated (the contacts opened)
by the latch head on the door while the door is closed.
The switch is intended to render the oven inoperative,
by means of blowing the C/T fuse, if the contacts of the
primary interlock relay (RY-2) and secondary interlock
switch fail to open when the door opens.
DESCRIPTION AND FUNCTION OF
COMPONENTS
Door Open Mechanism
The door is opened by pushing the open button on the
control panel. When the open button is pushed, it
causes the switch lever to lift up the latch heads. When
the latch heads are moved upward they release from
latch hook and the door opens. (See Figure 3-1)
Figure 3-1. Door Open Mechanism
Switches and Relays Interaction:
1. When the door is opened, the monitor switch con-
tacts close (to the ON condition) due to their being
normally closed. At this time the primary interlock
relay (RY-2) and secondary interlock switch are in
the OFF condition (contacts open) due to their
being normally open contact switches.
2. As the door goes to a closed position, the monitor
switch contacts are first opened and then the door
sensing switch and the secondary interlock switch
contacts close. (On opening the door, each of these
switches operate inversely.)
3. If the door is opened, and the primary interlock
relay (RY-2) and secondary interlock switch con-
tacts fail to open, the C/T fuse blows simultaneously
with closing of the monitor switch contacts.
Cavity Temperature Fuse
The cavity temperature fuse, located on the top of the
oven cavity, is designed to prevent possible fire damage
to the oven. If the food load is overcooked, by either
error in cook time or defect in the control unit, the cavity
temperature fuse will open. Under normal operation,
the cavity temperature fuse remains closed. However,
when abnormally high temperatures are reached within
the oven cavity, the cavity temperature fuse will open at
302°F (150°C), causing the oven to shut down.
NOTE: This fuse does not reset.
C/T Temperature Fuse
The C/T temperature fuse, located near the magnetron,
is designed to prevent damage to the magnetron if an
over heated condition develops in the tube due to cool-
ing fan failure, obstructed air guide, dirty or blocked air
intake, etc.
Under normal operation, the C/T temperature fuse
remains closed. However, when abnormally high tem-
peratures are reached within the magnetron, the C/T
temperature fuse will open at 302°F (150°C), causing
the oven to shut down.
1. The C/T fuse blows when the contacts (COM-NO)
of the primary interlock relay (RY-2) and secondary
interlock switch remain closed with the oven door
open and when the monitor switch closes.
2. If the wire harness or electrical components are
short-circuited, the C/T fuse blows to prevent an
electric shock or fire hazard.
NOTE: This fuse does not reset.
