If your freezer isn't cooling well and doesn't have an automatic defrost system, check for frost buildup inside the freezer. Manually defrosting the inside of the freezer regularly allows the refrigerant to cool the compartment properly so the temperature reaches 0 degrees.
If you hear rattling, knocking or loud whining noises from the compressor, you may need to replace the compressor. A faulty compressor won't compress the refrigerant in order to cool the freezer properly. A service technician will need to replace the compressor because that repair requires recovery and recharge of the refrigerant.
A failed cold control thermostat can also prevent the freezer from cooling properly. The cold control thermostat senses freezer temperature and turns on the compressor to keep the freezer compartment cold. If the cold control sensor fails or the internal contact inside the cold control isn't sending current to run the compressor, the freezer won't cool. If the compressor runs but doesn't stay on long enough to keep the freezer compartment at 0 degrees, you may need to replace the cold control thermostat.
For freezers with an automatic defrost system, a broken defrost heating element or failed defrost bi-metal thermostat can prevent the defrost system from melting frost off the evaporator. You'll typically see frost on the evaporator cover when the defrost system isn't working because the defrost heater isn't turning on to melt frost off the evaporator fins. The evaporator won't be able to cool the freezer well when the evaporator cooling fins are caked with frost because the frost blocks air passages over the fins.
A failed evaporator fan motor can also prevent the freezer from cooling well because cooling air won't circulate through the freezer compartment. If you don't hear the evaporator fan running inside the freezer when the compressor runs, you may need to replace the evaporator fan.
Some freezers use a condenser fan to cool down refrigerant before it enters the evaporator. A failed condenser fan motor can inhibit freezer cooling because air doesn't move across the condenser coils to cool the refrigerant before the refrigerant enters the evaporator. Also, check the condenser coils to see if the coils are dirty-dust on the coils can prevent air from cooling the refrigerant. Clean the condenser coils if dirty.
A failed electronic control board or a bad thermistor (also known as the temperature sensor) can also cause your freezer to warm up. If the thermistor doesn't sense that the freezer is warm, the electronic control board won't turn on the compressor. A faulty relay on the electronic control board can also prevent the control board from sending power to the compressor.
