KitchenAid KSSC36FKB00 Technical Education page 21

COMPRESSOR
The main control board supplies a 5 vdc, peak-
to-peak square wave, at 54 to 150 Hz, to the
inverter board. A standard VOM will read ap-
proximately 2.5 vdc. The inverter board sup-
plies the variable capacity compressor with
three-phase 230 vac. Varying the frequency
to the inverter board, and not the voltage,
changes the speed of the compressor. The
compressor can run at speeds of 1620 to 4500
rpm.
NOTE: It is not necessary, nor is it recom-
mended, to test the output of the inverter board.
While the compressor is running, its speed is
continuously updated. Speed is determined
after analyzing two factors:
• The difference between the actual tempera-
ture and the selected temperature settings.
• The rate of temperature change.
Minimum compressor speed is based on the
freezer's selected temperature setting, as
shown in the following chart.
Freezer Temperature
Setting (° ° ° ° F)
9 to –2
–3
– 4
–5
–6
–7
–8
–9
–10
The compressor generally cycles on and off
according to the cut-in and cut-out tempera-
tures of the freezer, however, the refrigerator
can turn on the compressor if the evaporator
fan is at maximum speed and the refrigerator
temperatures are not dropping.
Compressor
Minimum Speed
1620 rpm
1800 rpm
2000 rpm
2200 rpm
2400 rpm
2600 rpm
2800 rpm
3000 rpm
3200 rpm
3-3
COMPRESSOR PROTECTION
To protect the compressor and maintain effi-
ciency, minimum compressor off time is pro-
grammed into the control. When the compres-
sor turns off, a minimum of 7 minutes must
elapse before allowing a restart.
The inverter board utilizes a current limiting
device and thermal protection that eliminates
the need for a compressor mounted thermal
protector.
EVAPORATOR FAN MOTOR
The evaporator fan motor is a 12 vdc, variable
speed motor. The motor has four wires:
• A blue wire provides feedback to monitor the
speed of the motor.
• A red wire provides a constant 12 vdc.
• A yellow wire provides a variable voltage of
between 5 vdc and 17 vdc to control the
motor speed from 2000 to 3000 rpm.
• A white wire provides a common return.
EVAPORATOR FAN &
AIR DOOR DELAY
After defrost, an evaporator fan delay prevents
unnecessary movement of warm, moist air
through the refrigerator, by chilling the evapo-
rator prior to starting the fan. Immediately af-
ter defrost drip time, the compressor starts at
4500 rpm, but the evaporator fan is delayed
for 8 minutes. The air door remains closed for
8 minutes following defrost.
AIR DOOR
The air door is driven by a reversible DC
stepper motor. The motor operates on a 12
vdc, peak-to-peak square wave. Voltage is
delivered to the air door in a series of short
pulses. It is not possible to obtain a reliable
voltage reading with a VOM.
Separate windings are used to move the air
door open or closed. The door can be in any
one of 1800 positions from 0 to 90 degrees.
The air door is used to fine-tune the airflow to
the refrigerator.