Cooling Operation (Adaptive Defrost) - GE PSC21MGM Technical Service Manual

Cooling Operation (Adaptive Defrost)

During the cooling operation, the main control
board monitors door opening (fresh food and
freezer doors) and compressor run times. The
length of time between consecutive defrosts is
reduced by each door opening. If the doors are not
opened, the compressor will run up to 60 hours
between defrosts. If the doors are opened
frequently and/or for long periods of time, the
compressor run time between defrosts will be
reduced to as little as 8 hours.
Pre-Chill Operation (Adaptive Defrost)
When the main control board determines that
defrost is necessary, the main control board will
force the refrigerator into a continuous cool mode
(pre-chill). During pre-chill, the freezer temperature
may be driven below the temperature control panel
display setpoint. However, the fresh food
temperature will be regulated by the damper. Pre-
chill will last for 2 hours if it is not interrupted by
any door openings. If, after 8 hours, the unit has
been unable to complete an uninterrupted pre-chill,
it will proceed to the defrost cycle.
Defrost Heater Operation
PRE-CHILL MODE
F
F˚ / C˚
R
E
25˚ / -4˚
E
Z
20˚ / -7˚
E
R
15˚ / -9˚
A
10˚ / -12˚
I
R
5˚ / -15˚
T
E
0˚ / -18˚
M
08:00 09:00 10:00 11:00
P
-5˚ / -21˚
E
R
-10˚ / -23˚
A
T
U
-15˚ / -26˚
R
E
-20˚ / -29˚
S
After 2 hours of pre-chill operation or 8 hours of
interrupted pre-chill attempts, the main control
board turns the compressor, condenser fan, and
evaporator fan off. The main control board then
energizes the defrost relay, which completes the
defrost circuit.
During defrost operation, the main control board
monitors the evaporator temperature using
evaporator thermistor inputs. The thermistor will
terminate defrost heater operation usually in less
(Adaptive Defrost)
12:00 13:00 14:00 15:00 16:00 17:00 18:00
Pre-Chill Defrost
than 20 minutes. Typical defrost time is 20-30
minutes.
The defrost system is protected by a defrost
thermostat (switch). The thermostat opens when
the evaporator temperature raises to 140°
Fahrenheit and closes when the evaporator
temperature lowers to 110 degrees Fahrenheit.
Dwell Period (Adaptive Defrost)
After defrost heater operation has been terminated
by the main control board, a 5-minute dwell period
occurs. During this period, the compressor, the
condenser fan, and the evaporator fan remain off.
The remaining frost melting from the evaporator
will continue to drip and drain so the evaporator
will be totally clear of any moisture prior to the
cooling operation. After the 5 minute dwell period,
the unit goes into post dwell.
Post Dwell (Adaptive Defrost)
The post dwell period is designed to cool the
evaporator before circulating air within the
refrigerator. This prevents any residual heat on
the evaporator from being distributed in the
freezer. During this period, the compressor and
condenser fan are on, but all interior fans are off
and the damper is closed. Post dwell times vary
with different models. However, there is a 5-
minute maximum post dwell time.
Liner Protection Mode
The liner protection mode will activate if either of
the doors have been open for 3 minutes. This
mode will start the fans and close the damper.
This mode is controlled by 2 timers. Timer #1
monitors door-open time. A 3-minute door-open
count begins when the door is opened. If 3
minutes elapse before the door is closed, the liner
protection mode will become active. Once the
door is closed, timer #1 resets and liner protection
mode goes into standby.
In standby, normal fan and damper operations
resume and timer #2 begins a 3-minute door-
closed count. If 3 minutes elapse without a door
opening, liner protection mode will completely
deactivate. If a door is opened within the timer #2
door-closed count, the remaining time in the door-
closed count will be deducted from the timer #1
door-open count.
– 9 –