Sharp R-7H55 Service Manual Download Page 10

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R-7H55

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 control unit cause
the heating element relay to operate, thus the current to the
heating element is turned ON/OFF.

TURNTABLE MOTOR

The turntable motor drives the turntable roller assembly to
rotate the turntable.

CONVECTION MOTOR

The convection motor drives the convection fan and pro-
vides the heated air.

FAN MOTOR

The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and va-
pours given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity

HEATING ELEMENT

The heating element is located at the rear 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 rear 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 rear 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 continu-
ing 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
selected 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, damper cam and damper shaft.
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
condensation 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

1-1. When power supply cord is plugged in, a signal is

sensed in the control unit, and operates shut-off relay
(RY6).

1-2. Contacts of shut-off relay (RY6) close, the damper

motor is energized, opening the damper door.

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 of damper switch is re-sensed in the control

unit and shut-off relay (RY6) is turned off.

1-5. The A.C.line voltage to the damper motor is removed

and the motor turns off.