Refrigeration System - Whirlpool WRT138FZDB SERIES Service Manual

THEORY OF OPERATION

REFRIGERATION SYSTEM

OPERATION
The refrigeration system compares actual Refrigerator
Compartment (RC) temperature to the set-point temperature.
If the temperature is too warm, the sealed system operates to
cool the RC and Freezer Compartment (FC).
TEMPERATURE SET-POINTS
The refrigerator maintains the RC temperature at the
designated set-point. The temperature set-points for the RC is
set using the Control Box/User Interface (UI)in the RC. The UI
has three pre-determined set-points.
TEMPERATURE SENSING
The refrigerator compares the actual RC temperature to the
RC temperature zone set-point to determine when cooling
is necessary. Actual temperature of the RC is detected by a
thermistor located in the RC Air Diffuser.
Freezer Compartment Temperature Control
The Sealed System operates to cool the RC and FC
simultaneously in response to input received from the RC
thermistor. The FC temperature is derived by an air damper
controlling air flow to the RC.
Temperature Control Theory
The evaporator is located in the FC behind the rear wall. The
FC evaporator fan is mounted in front of the evaporator and
draws a suction on both the RC and FC. The evaporator and
fan are enclosed in a styrofoam air plenum containing an air
duct which directs a portion of the air down and into the RC
through an air damper located in the plenum. The remaining
portion of the air is directed into the FC.
The air damper is controlled by the Freezer Temperature
Selector Switch. This switch has three positions, the position
of the switch determines the volume of air flowing to the RC.
As the air damper is moved towards the MIN FC position, the
damper restricts air flow to the RC, and increases air flow to
the FC and cooling time required to satisfy the RC temperature
setpoint.
In this manner, the RC temperature remains near the UI
setpoint temperature, while the FC temperature changes
according to the position of the FC Temperature Selector
Switch.
SEALED SYSTEM
The sealed system uses a standard compressor to drive the
refrigeration cycle (FIGURE 2). Refrigerant is pumped through
the condenser and a UV Dye Drier to the Evaporator in the
FC. The compressor takes a suction on the outlet of the
evaporator.
2-4 18.2 Cu Ft Top Mount Refrigerator
n
For Service Technician Use Only
Evaporator
Compressor
AIR FLOW
Air flow in the temperature controlled compartments is
provided by the single evaporator fan located in the FC
evaporator area. Proper air flow allows efficient removal of
heat and uniform temperature distribution in each zone.
The air flow system uses a condenser fan to provide air flow in
the machine compartment, cooling equipment and removing
waste heat from the condenser.
REFRIGERATOR COMPARTMENT AIRFLOW
Airflow is driven by the FC evaporator fan. Air flow is directed
through the styrofoam plenum and FC damper to the RC.
FREEZER COMPARTMENT AIRFLOW
Airflow is driven by the FC evaporator fan. Air flow is directed
through the styrofoam plenum into the FC.
The FC Evaporator Fan is a single speed fan. It is powered by
120 VAC from Control Board connector CN1-3. It is wired in
parallel with and operates together with the compressor and
Condenser Fan.
MACHINE COMPARTMENT AIRFLOW
The Machine Compartment is cooled by the Condenser Fan.
The Condenser Fan is a single speed fan. It is powered by
120 VAC from Control Board connector CN1-3. It is wired in
parallel with and operates together with the compressor and
Evaporator Fan.
UV Dye
Drier
Condenser