Blue Seal E9311, Service Manual

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Revision 4/F3544
Convection Oven © Moffat Ltd, April 2005
3.3 EXPLANATION OF CONTROL
SYSTEM
The E9311 Turbofan convection oven range
features multi-function operator controls for
which a correct understanding of their
operation is required before carrying out any
service or fault repair work. The control
device functions are explained as follows.
These are broken into separate sections for
the oven and hob.
Convection Oven
The oven is electrically independent of the
hob, and has it’s own electrical supply and
connection.
A power switch on the control panel isolates
all power to the controls of the oven. With the
power switch Off all functions of the oven are
inoperable.
NOTE: The supply voltage is fed directly to
the input side of the power relay whenever the
electrical supply is on.
With the power switch On (illuminated) power
is directly supplied to the 60 minute bake
timer, door microswitch, light switch, and the
hold switch circuit. (On units manufacture
prior to serial number 232053 power is also
supplied directly to the temperature control
circuit). Accordingly the oven circulation fan
will operate when the door is closed, and with
door open the oven light will come on and the
circulation fan will shut down, as these are
controlled via the door microswitch. The
control panel light switch will turn the oven
light on when the door is closed only when the
light switch is held in.
The 60 minute timer is a mechanical timer and
can therefore be operated with the oven’s
power switch On or Off. However, only with
the oven’s power switch On will the switch
contacts of the 60 minute timer turn on the
time-up buzzer and illuminate the time-up
indicator on the control panel. The buzzer
and time-up indicator provide indication that
the time setting has run down to zero and at
this point will remain On continuously until the
60 minute timer has been manually set back
to the Off (vertical) position. The 60 minute
timer does not control any other part of the
oven’s operating system as this timer is
independent of the temperature control and
heating system.
For units manufactured from serial number
232054, power to the temperature control
circuit and elements is supplied via a power
relay located near the terminal block at the
rear of the unit. Although the power relay has
two poles with changeover contacts, only the
normally closed contact on one pole is used -
the other is redundant. When the power
switch on the control panel is switched on the
power relay is energised and the normally
open contact is closed, providing power to the
temperature control circuit.
The temperature control of this oven is with a
capillary type thermostat which can be set to a
required cooking temperature, or set to the
Grill/Broil position to provide top browning or
grilling/broiling in the oven.
The thermostat switch has a separate switch
body assembled onto the front from the shaft
assembly and when the thermostat is set to a
cooking temperature, one set of contacts is
closed to switch power from the oven
thermostat to the bottom heating element in
the oven. The second switch contact of this
switch assembly remains open in this setting
and isolates power from the top element inner
coil. The top element outer coil is directly
switched on from the oven thermostat.
Accordingly only the top outer element and
the bottom element are used when a cooking
temperature is selected. The control panel
indicator light above the thermostat knob
cycles On and Off with the thermostat to
indicate when the elements are on and the
oven is heating.
When the thermostat control is set to the Grill
position the first switch contact opens and the
second
switch contact closes. This
arrangement allows power to be provided to
the top element inner coil when the thermostat
is On, and isolates power from going to the
bottom heating element. The top element
outer coil which is directly fed from the oven
thermostat
switch is therefore On in
conjunction with the top element inner coil
when the thermostat is set to the Grill position.
As both the top inner and outer element coils
are thermostatically controlled, the elements
will cycle On/Off with the door closed as the
thermostat setting in the Grill position is 300°C
(600°F). If the Grill position is selected with
the door open, the elements will remain On
continuously and the circulation fan will be
turned Off. The control panel Grill indicator
will illuminate when the thermostat is set to
the Grill position and will cycle On and Off
with the main heating indicator light.
The E311 Turbofan convection oven features
a Roast-and-Hold system which can be used
to automatically set the oven to a fixed holding