Repair manual

OPERATION
3-12
er times out, power goes to the coil of a SPST
relay (13), allowing its contacts to close.
4. On a call for heat from the temperature controlĆ
ler (2), as sensed by the thermocouples, a set
of contacts closes sending power out of the
N.O. terminal of the temperature controller to
one side of a N.C. SPST thermal switch (14).
The switch toggles if the temperature passing
its face exceeds the rating on the back of the
switch.
NOTE: The switch is located in the slide out
control compartment. It protects the othĆ
er components from hi ambient heat.
If this switch is cold it should be closed, sendĆ
ing power to one side of another N.C. SPST
thermal switch (15). The switch toggles if the
temperature passing its face exceeds the ratĆ
ing on the back of the switch.
NOTE: The switch is located between two conĆ
vection blowers in the rear convection
fan compartment. It protects the other
components from hi ambient heat.
If this switch is cold it should be closed sending
power to one side of the SPST relay (13). This
relay was closed shortly after the 10 second
purge timer (12) timed out. Power is sent to terĆ
minal #1 of the Landis and Gyr ignition control
system (16). Terminal #8 of the ignition control
module is an output. It sends power to a 2 secĆ
ond purge timer (17) and the pilot valve (18).
The main valve (19) opens when the 2 second
purge timer times out. If the ignition control
senses a flame the system remains energized.
If not, the control locks out within 1 to 3 secĆ
onds. The ignition alarm light (20) illuminates.
NOTE: This system is polarity specific. If the
unit locks out repeatedly and the D.C.
microamps are within the acceptable
range, check for proper polarity.
5. When power is applied to the coil of the motor
contactor (3) the contacts close sending powĆ
er to the two convection fans (5) located in the
rear of the oven.
NOTE: Terminals #13 and #14 of the motor
contactor act as a hood interlock. They
are sometimes used as a means of
starting the hood.
6. There are two cooling fans (21) located in the
rear convection fan compartment. These fans
are activated when the N.O. SPST thermal
switch (22) closes due to high ambient heat.
The switch toggles if the temperature passing
its face exceeds the rating on the back of the
switch.
NOTE: The switch is located between the two
blowers in the rear convection fan
compartment. It protects the convecĆ
tion fans from hi ambient heat.
A third cooling fan (21) is located in the control
box compartment. This fan is activated when
another N.O. SPST thermal switch (23) closes.
The switch toggles if the temperature passing
its face exceeds the rating on the back of the
switch.
NOTE: The switch is located in the slide out
control compartment. It protects the
controls from hi ambient heat.
7. The conveyor is driven by an open loop D.C.
control system consisting of a conveyor switch
(24), time display (25), 10kW potentiometer
(26), D.C. speed control board (27), 180 VDC
motor (28) and #10 Hall effect pickup (29). AfĆ
ter the conveyor switch is turned on, the time
display illuminates. The D.C. control board
powers up. The output voltage measured on
terminals A1 and A2 of the board to the motor
varies from 20 to180 VDC based on the posiĆ
tion of the potentiometer. The speed of the moĆ
tor should also vary. The time display varies deĆ
pending on the speed of the Hall effect pickup.
The pickup sends an R.P.M. value to the disĆ
play. The display converts this value to minĆ
utes:seconds.
NOTE: This type of system does not sense the
weight of the product and will slow
down slightly if the belt is fully loaded.