Sub-Zero Refrigerator Not Cooling? Repair Cost and Diagnosis

Your Sub-Zero refrigerator is running, but the fresh-food section is getting warm. In another situation, the freezer may stop freezing while the refrigerator continues working normally.

Sometimes both sections become warm at the same time.

Does this mean the refrigerator needs a new compressor or must be replaced?

Not necessarily.

Many Sub-Zero combination refrigerators use separate refrigeration systems for the refrigerator and freezer. This means one section can stop cooling while the other continues working. Sub-Zero confirms that many 500, 600, later 700, Classic, Designer, and PRO combination models have two compressors, although the number varies by product and model.

A failed compressor start relay is one possible cause. When both sections are warm, a dirty condenser, failed condenser fan, power problem, or another shared component may be more likely.

The Issue: One or Both Sections Are Not Cooling

Common symptoms include:

• The refrigerator section is warm, but the freezer still works.
• The freezer is warm, but the refrigerator remains cold.
• Both sections are becoming warm.
• One compressor repeatedly clicks but does not start.
• The appliance hums, clicks, and then becomes quiet.
• The compressor attempts to start every few minutes.
• The refrigerator displays a Service or Vacuum Condenser message.
• The area around the grille or door frame feels unusually hot.
• The refrigerator runs continuously but cannot reach temperature.

Sub-Zero uses separate refrigerator and freezer systems on many combination models. This allows each compartment to maintain its own temperature and humidity.

When only one compartment is warm, the problem may be limited to that compartment’s compressor, start device, evaporator fan, sensor, control, or sealed refrigeration system.

When both compartments are warm, the technician should first look for a problem affecting the entire refrigerator.

How to Diagnose a Sub-Zero That Is Not Cooling

Confirm which section is affected

Check the actual temperature in both compartments.

The refrigerator should generally be close to 38°F, while the freezer should be approximately 0°F. Temperature can fluctuate after the door has been open or after a large amount of food has been added, and Sub-Zero advises allowing up to 24 hours after changing a temperature setting.

Determine whether:

• Only the refrigerator is warm
• Only the freezer is warm
• Both compartments are warm

This information is important because many Sub-Zero models have independent cooling systems.

Check the controls and power

Make sure the affected section has not been accidentally switched off.

Look for:

• Service messages
• Error codes
• A flashing Vacuum Condenser message
• Unusual temperature readings
• A recent power interruption

Resetting the appliance may clear a temporary control problem, but it will not repair a defective relay, fan, or compressor. Sub-Zero recommends professional service when normal resetting and temperature checks do not restore cooling.

Clean the condenser

A dirty condenser is one of the first things to check when a Sub-Zero is running continuously or not cooling properly.

Dust and pet hair restrict airflow through the condenser. This makes the compressors work harder, increases operating temperatures, and can reduce cooling performance.

Turn the appliance off using the control or circuit breaker before cleaning. Access instructions vary by series, so follow the correct procedure for the model.

Sub-Zero specifically recommends condenser cleaning when the appliance is warm, runs excessively, or displays a Vacuum Condenser or Service message.

Listen near the compressor area

The compressors and condenser fan are normally located behind the upper or lower grille, depending on the model.

Listen for:

• Repeated clicking
• A compressor that hums but does not start
• A compressor that starts and quickly shuts down
• A rattling or vibrating fan
• No sound from the affected compressor

Repeated clicking can indicate that the compressor is trying and failing to start. A defective start relay or overload device is one possible cause, but the compressor itself, wiring, power supply, or control may also be responsible.

Do not repeatedly cycle the power or attempt to test a compressor using exposed live wiring. Compressor diagnosis involves electrical components and should be completed by a qualified technician.

Check the condenser fan

The condenser fan removes heat from the compressor and condenser area.

On many Sub-Zero models, the fan cycles according to compressor operation. If the fan does not run when required, heat can build up and both refrigerator systems may lose cooling performance. Sub-Zero notes that fan humming or vibration can indicate a condenser-fan problem.

Possible condenser-fan symptoms include:

• Both refrigerator sections becoming warm
• Compressors running for long periods
• An unusually hot grille or cabinet frame
• A humming, rattling, or grinding noise
• Little airflow around the condenser
• Compressors overheating and shutting down

Sub-Zero identifies a condenser-fan malfunction as one possible cause when the exterior frame becomes excessively hot.

The Likely Solution

If the compressor start relay has failed

The start relay provides the electrical assistance needed to start the compressor.

If the relay is burned, weak, or internally damaged, the compressor may click or hum without starting. The technician should test:

• Incoming voltage
• Start relay
• Overload protector
• Compressor windings
• Wiring and terminals
• Control output

If the compressor tests correctly and the start device has failed, replacing the start relay may restore normal cooling.

On a dual-compressor Sub-Zero, each compressor has its own starting components. A refrigerator-side relay problem may affect only the fresh-food compartment, while a freezer-side problem may affect only the freezer.

If the condenser fan has failed

A failed condenser fan should be replaced, and the condenser area should be thoroughly cleaned.

The technician should also inspect the fan blade, wiring, mounting, and power supplied to the motor.

If the fan has been inoperative for an extended period, both compressors should be checked for overheating.

Other possible causes

A warm Sub-Zero can also be caused by:

• Evaporator fan failure
• Temperature sensor failure
• Fan or door switch failure
• Control-board or relay problem
• Refrigerant leak
• Restricted sealed system
• Failed compressor
• Damaged door gasket

If a refrigerator or freezer fan switch fails, Sub-Zero notes that the compartment may be cold at the bottom but warm near the top.

Technician’s Recommendation: Repair or Replace?

As an appliance technician, I normally recommend repairing a Sub-Zero refrigerator when the problem is a start relay or condenser fan.

Sub-Zero is a high-end built-in appliance. Replacing it can be extremely expensive and may also require professional removal, installation, cabinetry adjustments, and disposal.

A relay or fan repair is normally a small fraction of the replacement cost.

However, the relay must be properly tested. Replacing a start relay will not solve the problem if the compressor is internally damaged or the sealed system has failed.

When only one compartment is warm, the independent dual-compressor design can be an advantage. The technician may be able to repair one refrigeration system without replacing the entire appliance.

Sub-Zero Cooling Repair Prices

Typical TrustedFix pricing may include:

Compressor start-relay repair

• Start relay and related components: approximately $180–$300 per compressor
• Professional labour: approximately $280–$360
• Estimated repair for one compressor: approximately $460–$660

If both compressor start devices require replacement, the parts cost may approximately double. Labour depends on model design, access, and the testing required.

Condenser-fan repair

• Condenser fan or fan assembly: approximately $300–$600
• Professional labour: approximately $280–$360
• Estimated repair: approximately $580–$960

These are general Canadian estimates before taxes, travel charges, and additional repairs.

Compressor or sealed-system repairs can cost significantly more and require a separate estimate.

Book a Sub-Zero Refrigerator Repair

If your Sub-Zero refrigerator, freezer, or both sections are warm, begin by checking the controls and cleaning the condenser.

If you hear repeated clicking, the compressor does not start, or the condenser fan is not operating, professional testing is required.

TrustedFix Appliance Repair can test the start relay, compressor, condenser fan, sensors, wiring, controls, and sealed refrigeration system before recommending a repair.

Because Sub-Zero is a high-end built-in appliance, an accurate diagnosis is especially important. In many cases, repairing a failed relay or condenser fan is considerably less expensive than replacing the refrigerator.