1. Open the freezer door and listen for the fan motor. If the fan is not heard, or if there is any unusual noise, replace the fan motor. In some units, the fan motor will not operate if the freezer door is opened; find the push button around the freezer door and push it while the door is open and listen to the fan. If you can hear the fan, or if it sounds like it is operating at a reduced speed.
2. Disconnect the power.
3. Remove the evaporator cover (explained earlier in “Testing the Defrost Limit Switch”) and remove the fan support plate. (A long running time with an inoperative fan can be evidenced by an accumulation of ice on the evaporator plate).
4. If the fan does not run, check to see if there is power at the motor terminals with a test light. (As explained in “Testing the Condenser Fan Motor,” step 4). Take care not to touch any live wires while the unit is plugged in.
If there is power at the fan motor and it is not running, replace the fan motor.
Sometimes, defective fan motors run for a while, but due to an internal short, after a brief period of running, heat up and stop operating. Sometimes the fan runs, but it appears not to be running at full speed. This ohmmeter
test will determine whether or not it is defective. If the ohmmeter registers a reading ±5% beyond the factory ohm rating, or if no-continuity reading is registered, replace the fan motor. Refrigeration units manufactured by General Electric, in particular, and many other brands come with schematic wiring diagrams (covered in detail in the “Basic Electricity” chapter) that indicate the ohm value of each electrical component.
When replacing fan motors, check for the watt rating and the revolution per minute of the replacement part. The new fan motor should be rated as close to the original part as possible. This is particularly important in commercial refrigeration considering the fan speed variation in those units.
Often, replacement commercial fan motors come with fan blade shafts that are too long. Measure the length needed and cut off the excess with a hacksaw. During installation, pay close attention to the direction of its rotation. It is stamped CW for clockwise or CCW for counterclockwise on the back of the motor or on the nameplate. The new fan motor must rotate in the same direction as the original.
This is made simple in commercial fan motors (see fig. 61). Usually, two extra wires come out of the motor. By connecting these two wires together, the shaft rotation can be reversed. Instructions to this effect are supplied with new motors.