Model Frigidaire #FFU20F9GW3 reaches set temp but wont come on .

The number you gave is for a straight up freezer, is that correct?

Cause 1

Start Relay

The start relay works in conjunction with the start winding to start the compressor. If the start relay is defective, the compressor may sometimes fail to run or may not run at all. As a result, the refrigerator will not be cold enough. To determine if the start relay is defective, use a multimeter to test it for continuity between the run and start terminal sockets. If the start relay does not have continuity between the run and start terminal sockets, replace it. In addition, if the start relay has a burnt odor, replace it.

Cause 2

Temperature Control Thermostat

The temperature control thermostat directs voltage to the compressor, evaporator fan motor, and condenser fan motor (if applicable). If the temperature control thermostat is not working properly, it may prevent the refrigerant system from running. To determine if the thermostat is defective, rotate the thermostat from the lowest setting to the highest setting and listen for a click. If the thermostat clicks, it is not likely defective. If the thermostat does not click, use a multimeter to test the thermostat for continuity. If the temperature control thermostat does not have continuity at any setting, replace it.

Cause 3

Temperature Control Board

The temperature control board provides voltage to the compressor and fan motors. If the temperature control board is defective, it will stop sending voltage to the cooling system. However, this is not a common occurrence. Control boards are often misdiagnosed—before replacing the control board, first test all of the more commonly defective components. If none of the other components are defective, consider replacing the temperature control board.

Cause 4

Thermistor

The thermistor monitors the refrigerator temperature and sends the temperature reading to the control board. The control board regulates power to the compressor and evaporator fan based on the thermistor readings. If the thermistor is defective, the compressor and evaporator fan may not run when necessary. As a result, the refrigerator will not be cold enough. To determine if the thermistor is defective, test it with a multimeter. The thermistor resistance should change in conjunction with the refrigerator temperature. If the thermistor resistance does not change, or the thermistor does not have continuity, replace the thermistor.