Lennox MCB Series Service Manual page 12

Description: When the indoor fan speed is to low or to high undeterminate amount of time, the LED displays the failure
code and the system turns off.
2. Indoor unit Fan motor:
a. Power off and disconnect fan motor power cord from the PCB. Measure the
resistance value of each winding by using a multimeter. The normal values
are show as shown to the right.
b. Power on the system and set the unit running in fan mode at the highest fan
speed. After running for 15 seconds measure the voltage of pin 1 and pin
2. If the value of the voltage is less than 100V (208~240V power supply) or
50V (115V power supply)the indoor control PCB has an issues and will need
to be replaced.
Input Terminals
12