Heat Pump Not Defrosting Properly Greater Vancouver

A properly functioning defrost cycle is essential for heat pump heating in Greater Vancouver winter — when it fails, ice accumulates on the outdoor coil and heating performance drops dramatically.

What This Means

The heat pump defrost cycle temporarily reverses the system to heating the outdoor coil, melting the frost that accumulates during normal heating operation. A properly working defrost cycle runs for a few minutes every 30 to 90 minutes and then returns to normal heating mode.

Common Causes

• Defrost control board failure — does not initiate defrost when needed
• Defrost temperature sensor failure — does not detect when coil temperature requires defrost
• Defrost timer failure in older systems without demand-defrost
• Outdoor fan motor not running — excessive frost accumulates quickly without airflow
• Reversing valve sticking — system attempts defrost but cannot reverse to warm the outdoor coil
• Low refrigerant — coil operates too cold and frosts rapidly, overwhelming normal defrost frequency

What Homeowners Can Check Safely

• If the outdoor unit is completely encased in ice, turn the system off and allow it to thaw outdoors — do not chip ice off the coil fins
• Note the outdoor temperature when icing occurs — mild humid days around 0 to 5 degrees Celsius are highest-frost conditions for heat pumps

When to Call a Licensed Technician

Heat pumps contain refrigerant under pressure, electrical components at line voltage, and control systems that require specialized diagnostic tools. Do not open refrigerant circuits, bypass safety switches, or attempt to recharge refrigerant without proper certification.

• Defrost board diagnosis and replacement
• Defrost sensor testing (resistance measurement versus temperature)
• Outdoor fan motor testing
• Reversing valve coil testing
• Refrigerant pressure testing to rule out refrigerant-related icing

Frequently Asked Questions

How long does a heat pump defrost cycle take?

A normal defrost cycle lasts 2 to 10 minutes. During defrost, the outdoor fan typically shuts off, the outdoor coil warms and steam may be visible as frost melts, and the backup electric heat may run to maintain indoor comfort. After defrost, the system returns to normal heating mode. A defrost cycle that lasts over 15 minutes or that seems to run frequently without clearing the ice suggests a defrost system problem.

Why does my heat pump make a whooshing sound during defrost?

The whooshing or hissing sound during defrost is the reversing valve switching — the valve changes refrigerant flow direction to reverse the cycle and warm the outdoor coil. This sound is normal and lasts only a second or two. You may also hear the outdoor fan stop and restart. These are all normal defrost cycle sounds.

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