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MFI Series Control System Diagnostics
Page 23
The Control System consists of:
●Control Board
●Water Sensors
●Ice Sensors
●High Pressure Cut Out
●Low Pressure Cut Out
If the unit is OFF, check the control board:
1. Is the Power OK light on? If not check power to the unit. If it has power, and the Power OK light is not on,
check the high pressure and low pressure cut outs. If they are both closed, replace the board. If the
POWER OK light is ON, go to the next step.
2. Is the Water OK light on? If it is, go to the next step. If not, check the water level in the reservoir. If there is
water in the reservoir, check that the water sensor is plugged in. To check the water sensor:
a. Unplug the water sensor.
b. Pull the water sensor from the reservoir.
c. Place one ohmmeter lead on the sensor’s plug and the other on the sensor’s tip. The meter should
show nearly zero (0) resistance. If it reads infinite resistance, check the tip for corrosion. If it is clean and
still reads open, replace the sensor.
OR
, connect a copper wire to the wire where the water sensor plugs into and place the other end in the
water. The WATER OK should go ON. If it does not, replace the board.
3. Ice sensor Check. Is the BIN FULL light OFF? If it is OFF and the SERVICE light is OFF and the unit is not
running, replace the control board.
a. If it is OFF and the auger motor is running but the compressor is not, check the compressor contactor coil.
b. If it is ON, the ice sensors may be blocked. Remove them and check for mineral scale.
4. High pressure cut out check.
a. Disconnect electrical power.
b. Pull the wires off the high pressure cut out.
c. Use an ohmmeter to determine if the switch is OPEN. If it is, check the discharge pressure. If the
discharge pressure is less than 300 PSIG, replace the high pressure cut out.
d. If the high pressure cut out is open and the system has high discharge pressure, check for the cause.
5. Low pressure cut out check.
a. Disconnect electrical power.
b. Pull the wires off the low pressure cut out.
c. Use an ohmmeter to determine if the switch is OPEN. If it is, check the suction pressure. If the suction
pressure is greater than 20 PSIG, replace the low pressure cut out.
d. If the low pressure cut out is open and the system has low suction pressure, check for the cause.