Compressor Protection - KitchenAid KBFC42FS Technical Education

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 voltage and
frequency to the inverter board 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 recommend-
ed, 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)
6 to –2
–3
–4
–5
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
3-3

COMPRESSOR PROTECTION

To protect the compressor and maintain ef-
ficiency, minimum compressor off time is pro-
grammed into the main control board. When the
compressor turns off, a minimum of 7 minutes
must elapse before allowing a restart.
At the end of the 7-minute period, the condenser
fan motor starts, and the main control board
sends the compressor speed signal to the
inverter. The compressor will not start for an
additional minute, due to the inverter delay.
The inverter utilizes a current-limiting device
and thermal protection that eliminates the need
for a compressor-mounted thermal protector.
The inverter will not allow a compressor restart
for 8 minutes after the compressor turns off.
This inverter delay will not occur after a power
interruption, because inverter memory is lost
(see "Power Interruption" on page 3-4).
EVAPORATOR FAN MOTOR
The evaporator fan motor is a 12 vdc, variable
speed motor. The motor has four wires:
• A blue wire that is not used.
• 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 evapora-
tor prior to starting the fan. Immediately after
defrost drip time, the compressor starts at
4500 rpm, but the evaporator fan is delayed for
8 minutes. Also, the air door remains closed
during the 8-minute delay.