Convection Cooking System; Microwave Cooking - Sharp R-1880LS Service Manual

R-1880LS/LST
The hood lamps are mounted at the hood lamp angle on the base
cover. When the hood lamp button is pushed, the hood lamp relay
(RY8) contacts close turning both hood lamps on.
HEATING ELEMENT
The heating element 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
heating element.

CONVECTION COOKING SYSTEM

This oven is designed with a hot air heating system where food is
not directly heated by the heating element, but is heated by forced
circulation of the hot air produced by the heating element.
The air heated by the heating element is circulated through the
convection passage provided on the outer casing of the oven cavity
by means of the convection fan which is driven by the convection
motor. It then enters the inside of the oven through the vent holes
provided on the left side of the oven. Next, the hot air heats the
food on the turntable and leaves the oven cavity through the vent
in the center of the oven cavity left side wall.
Without leaving the oven, this hot air is reheated by the heating
element, passes through the convection passage and enters the
inside of the oven cavity again, in a continuing cycle.
In this way, the hot air circulates inside the oven cavity to raise
its temperature and, at the same time, comes into contact with
the food being cooked.
When the temperature inside the oven cavity reaches the se-
lected temperature, the heating element is de-energized. When
the temperature inside the oven cavity drops below the selected
temperature, the heating element is energized again. In this way,
the inside of the oven cavity is maintained at approximately the
selected temperature.
When the convection time reaches 0, the heating element is de-
energized and the convection fan stops operating and the oven
shuts off.
DAMPER OPEN-CLOSE MECHANISM
Usually, the damper is in the open position except during convection
cooking. Damper position is set automatically by damper motor,
damper switch and motor cam. These components are operated by
a signal that judges if microwave cooking or convection cooking
operation is selected by the control unit.

Microwave Cooking:

Damper is in the open position, because a portion of cooling air
is channeled through the cavity to remove steam and vapors given
off from the heating foods.
It is then exhausted at the top of the oven cavity into a condensa-
tion compartment.
Convection Cooking:
Damper is in the closed position, so that no hot air will be allowed
to leak out the oven cavity.
Damper Operation
1. When power supply cord is plugged in:
1-1. When power supply cord is plugged in, a signal is sensed
in the control unit, and operates shut-off relay (RY6).
1-. Contacts of shut-off relay (RY6) close, the damper motor
is energized, opening the damper plate.
1-3. When the damper is moved to the open position by
the damper cam the damper switch is closed (ON
position).
1-4. The signal from damper switch is re-sensed in the control
unit and shut-off relay (RY6) is turned off.
1-5. The 10 volts A.C. to the damper motor is removed and
the motor turns off.
. When oven is microwave cooking:
Damper is in the open position.
3. When oven is convection cooking:
3-1. Damper motor is energized by touching the convection,
temperature, number and START pads.
3-. When damper is in the closed position (damper switch is
OFF), its signal is sensed by the control unit, and shut-off
relay (RY6) is de-energized.
3-3. The damper is held in the closed position during the
convection cooking operation.
3-4. At the end of the convection cooking, shut-off relay
(RY6) is energized, and the damper is returned to the
open position.
NOTE: If the damper plate is not in the proper position, closed
during convection or open during microwave, the control
unit will stop oven operation after 1 minute.
Figure D-2. Damper Mechanism
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DAMPER PLATE
DAMPER CAM
DAMPER SWITCH
DAMPER MOTOR