Description And Function Of Components; Oven Thermal Cut-Out; Monitor Switch; Upper And Lower Latch Switches - Sharp R-9H10 Service Manual

R-9HlO
DESCRIPTION AND FUNCTION OF COMPONENTS
THERMISTOR
The thermistor is a negative temperature coefficient
type. The temperature in the oven cavity is detected
through the resistance of the thermistor, and then the
CPU unit causes the heater relay to operate, thus the
current to the convection heater is turned ON/OFF.
OVEN THERMAL CUT-OUT
The oven thermal cut-out located on the right side of
the thermal protection plate is designed to prevent
damage to the convection heater unit if an overheated
condition develops in the tube due to cooling fan fail-
ure, obstructed air ducts, dirty or blocked air intake, etc.
Under normal operation, the oven thermal cut-out re-
mains closed. However, when abnormally high tem-
peratures are reached within the heater unit, the oven
thermal cut-out will open, causing the oven to shut
down.
When the oven has cooled temperature, the oven
thermal cut-out closes.
(RD72407U')
MO'NITOR SWITCH
The monitor switch is mounted on the latch hook. It
is activated (the contacts opened) by the upper latch
head when the door is closed. The switch is intended
to render the oven inoperative by means of blowning
the fuse when the contacts of the common and normal
open contacts of upper latch switch fail to open when
the door is opened.
Functions:
I. 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 the common and
normal open contacts of upper latch switch are in
the OFF condition (contacts open) due to their
being normally open contacts switch.
2. As the door goes to a closed position, the monitor
switch contacts are first opened and then the
common and normal open contacts of upper latch
switch close. (On opening the door, each of these
switches operate inversely.)
3. If the door is opened during cooking, and the
common and normal open contacts of upper latch
switch fail to open, the monitor fuse blows simul-
taneously with closing of the monitor switch con-
tacts
CAUTION:BEFORE REPLACING A BLOWN FUSE
TEST THE UPPER LATCH SWITCH AND
MONITOR SWITCH FOR PROPER
OPERATION.( REFER TO CHAPTER "TEST
PROCEDURE").
AFTER REPLACING FUSE ALSO REPLACE
MONITOR SWITCH.
STOP -SWITCH
The stop switch is activated by the latch head.
When the door is opened while the oven is in cook
cycle, the stop switch contacts open to de-energize the
relay( RY-1 ,RY-2,RY-3,RY-5,RY-6).
Then the cook cycle is stopped.
(RD72EOl U')
UPPER AND LOWER LATCH SWITCHES
Those latch switches are mounted in the latch hooks
as shown in figure. They are activated by the latch
heads on the door.
When .the door is opened, the switches interrupt the
circuit to all components except CPU unit and relay
unit and oven lamp. A cook cycle cannot take place
until the door is firmly closed thereby activating both
interlock switches.
.A
LATCH HOOK
LATCH
HEAD
/
UPPER LATCH SWITCH
STOP SWITCH
MONITOR FUSE
MONITOR SWITCH
LOWER LATCH SWITCH
SWITCH LEVER
OPEN LEVER
DOOR OPEN BUTTON
Figure D-l. Upper Latch Switch, Lower Latch
Switch, Monitor Switch and Stop Switch
CONVECTION HEATER
The convection heater is located at the left side of the
oven cavity. It is intended to heat air driven by the
convection fan. The heated air is kept in the oven and
force-circulated and reheated by the convection heater.