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HomeRepair HelpSub Zero Refrigerator RepairSub Zero Refrigerator runs constantly Repair
Sub Zero Refrigerator runs constantly
If your Sub Zero refrigerator is running constantly, you can narrow the problem quickly by checking a few things in order. Start with the room: refrigerators work best between 60 and 95 F, and hot, humid air will make the unit run more. If the room is fine, suspect the compressor next; an inefficient compressor can cause the refrigerator compressor to run continuously even when fans and sensors look okay. Also check the freezer temperature — many models feed cold air from the freezer to the fridge, so a freezer warmer than about 0 to 5 F (or above 10 F in severe cases) will keep the fridge running. Make sure doors are closing fully and nothing is blocking the gasket. If airflow seems restricted or frost builds on the evaporator, the defrost heater or defrost thermostat may be faulty; test the heater and thermostat for continuity with a multimeter and replace any part that fails. Want the exact replacement part for your unit? Enter your model number on RepairClinic.com to find the right part for your appliance.
01 - Room Temperature is Hot
Normal operating temperatures for a refrigerator are between 60 and 95 degrees Fahrenheit (16 and 35 degrees Celsius). The hotter and more humid the air is the less efficient the refrigerator will be, causing it to run more. If possible, keep the refrigerator within the recommended operating temperatures and as cool as possible.
Top Solution
02 - Sub Zero Refrigerator Compressor
The compressor is the component that pumps refrigerant through the sealed system to cool the appliance. If you've determined the fan motors are all working and the thermistor is accurately monitoring the air temperature, it's possible the compressor itself is inefficient, resulting in it running continuously, although this is not a common problem.
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Highly Likely
03 - Freezer Temperature is Above 10 Degrees F (-12C)
Since the refrigerator compartment gets its cold air from the freezer compartment for many model types ("Top Freezer", "Bottom Freezer", and "Side by Side" models, for example), the refrigerator compartment will take longer to cool down if the freezer is not cold enough. As a result, the compressor may run constantly. The freezer temperature should be set between 0 and 5 degrees Fahrenheit (-18 to -15 Celsius).
Highly Likely
04 - Door Not Fully Closing
Check to see that the doors are closing properly. If a door bin or food item is keeping the door open slightly the refrigerator may not cool properly, which can cause the refrigerator to run constantly.
Highly Likely
05 - Sub Zero Refrigerator Defrost Heater Assembly
The defrost heater assembly turns on several times throughout the day to melt away any frost that may have accumulated on the evaporator coils. If the defrost heater assembly is defective, the refrigerator will not defrost, and frost will continue to accumulate on the evaporator coils. If the evaporator coils are frosted over, the refrigerator will work harder to remove the heat. As a result, the refrigerator will run constantly in an effort to cool down. To determine if the defrost heater is defective, use a multimeter to test it for continuity. If the defrost heater does not have continuity, replace it.
Common
06 - Sub Zero Refrigerator Defrost Thermostat
If the refrigerator runs constantly, the defrost thermostat might be defective. Several times a day the defrost heater turns on for a few minutes to melt away any frost that may have accumulated on the freezer or refrigerator evaporator coils. In order for this to work, the defrost thermostat has to sense that the coils are cold enough. If the coils are cold enough the defrost heater will turn on. If the thermostat is defective it may not be able to sense the temperature of the coils and then won't turn on the defrost heater. If the defrost heater doesn't turn on, the frost will build up on the coils and eventually no air ...
Common
07 - Sub Zero Refrigerator 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 both the condenser fan motor and evaporator fan motor are running, you should test it with a multimeter. The thermistor resistance should change in conjunction with the refrigerator temperature. If the thermistor resistance does not change, it's possible the component is sending an inaccurate temperature reading to the control board resulting in the refrigerator running constantly. A new thermistor should be i...
Common
Frequently Asked Questions
My refrigerator runs constantly. What should I check first?
Freezer is cold but refrigerator runs constantly. Why is the fridge not cooling?
How do I test the defrost heater and defrost thermostat?
Could a bad compressor cause my refrigerator to run continuously?
How do I enter my model number to find the right replacement part on RepairClinic.com?