Why Your Sub-Zero Refrigerator Runs Constantly

Unlike standard refrigerators, a Sub-Zero refrigerator is designed to run longer cycles to maintain extremely stable internal temperatures. However, continuous operation 24/7 is not normal — and it is often the earliest warning sign of a failing cooling system.

Catching this early can prevent a $2,000–$4,000 sealed-system repair.

Normal vs Abnormal Operation

A Sub-Zero refrigerator typically runs:

• 60–80% of the day in warm climates
• 40–60% in mild climates like the San Francisco Bay Area

It should still:• cycle off
• defrost periodically
• maintain quiet compressor behavior

If it never shuts off — something is forcing the compressor to overwork.

6 Most Common Causes

1. Dirty Condenser Coils

Luxury refrigerators are extremely sensitive to airflow.

Pet hair, kitchen grease, and dust accumulate on the condenser under the unit.
This prevents heat from leaving the system.

Result:
The compressor runs continuously trying to remove heat.

This alone accounts for over 40% of service calls.

2. Failing Door Gaskets

A microscopic air leak forces the refrigerator to constantly replace cold air.

Signs:
• condensation on shelves
• food spoiling quickly
• motor noise at night

3. Defrost System Failure

Sub-Zero uses a controlled defrost heater system.
When it fails, frost forms behind the evaporator cover and blocks airflow.

The refrigerator thinks it is warm — so it never stops running.

4. Evaporator Fan Motor Issues

If the internal fan slows down, cold air cannot circulate.

The control board responds by:
→ increasing compressor runtime.

This is extremely common in 8–15 year old units.

5. Low Refrigerant (Sealed System Leak)

This is the most serious condition.

A small refrigerant leak causes:
• endless running
• freezer OK but refrigerator warm
• food freezing in certain sections

This requires sealed-system repair performed by a specialist.

6. Failing Compressor

If the compressor valves wear out, it loses compression efficiency.
The refrigerator still cools — but never reaches target temperature.

The system compensates by running nonstop.

When You Should Call Immediately

Call for service if you notice:

• refrigerator warm but freezer cold
• ice cream soft
• unit hot to the touch
• loud humming at night
• motor running 24 hours

These are early sealed-system warnings.

Why Early Diagnosis Matters

Sub-Zero refrigerators are designed to be repairable for 20+ years — but only if problems are addressed early.

Running continuously causes:
• compressor burnout
• oil contamination
• evaporator damage

A maintenance visit often prevents a major repair.

Professional Sub-Zero Service in the Bay Area

We at Commercial Home Products service both residential luxury kitchens and light commercial refrigeration systems including:

• built-in refrigerators
• undercounter units
• wine storage
• restaurant prep refrigerators

We provide diagnostic service and maintenance for homes and businesses throughout the San Francisco Peninsula. Call at (650) 712-0117.