Heat Pump Defrost Noise — What Is Normal and What Is Not

Published: July 23, 2026 — BC Wide Home Services Ltd, doing business as BC Wide Heating & Air Conditioning — Greater Vancouver, BC

Normal Defrost Sounds

Whooshing sound when the reversing valve shifts (refrigerant flow reverses) — lasts 5-10 seconds. Water dripping from the outdoor unit as frost melts — can last 5-15 minutes. Steam rising from the unit — normal defrost operation. The outdoor fan stops during defrost — also normal. The indoor temperature may drop slightly during defrost.

Abnormal Defrost Sounds

Loud banging when the reversing valve shifts — indicates valve struggling to shift (low refrigerant or failed solenoid). Grinding or rattling from the outdoor unit during defrost — fan blade hitting ice buildup. Continuous gurgling — abnormal refrigerant flow. No defrost sounds at all — defrost cycle may not be activating.

When to Call for Service

Call for service if: the defrost cycle does not activate at all, ice accumulates despite the unit running, defrost runs for more than 20 minutes without stopping, the indoor temperature drops significantly during defrost (auxiliary heat not engaging), or you hear loud banging or grinding during defrost.

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Safety Reminder

If you smell gas, suspect carbon monoxide or believe there is an immediate danger, leave the property and contact emergency services or the appropriate gas emergency authority. Do not remain inside — exit the building immediately and call for help from outside.