Steam rising from an outdoor heat pump, a fan that suddenly goes quiet, or a light coating of frost can look alarming during a Spokane cold snap. Most of the time, those signs mean the system is protecting itself through a normal defrost cycle. Not that something has broken.
We’ve served Greater Spokane since 1945, and we know Spokane winters don’t follow one pattern. Damp air near freezing can frost an outdoor coil fast, while much colder, drier air may produce less frost even when temperatures drop well below zero.
Why Spokane Cold Snaps Trigger Defrost Cycles
The outdoor coil (the finned surface that pulls heat from outside air) can run colder than the surrounding air temperature while the heat pump is operating. That means moisture can freeze onto the coil even when the thermometer reads above 32 degrees Fahrenheit. Spokane winters bring below-freezing temperatures, snowfall, and precipitation from roughly November through March, giving frost plenty of chances to build up whenever moisture is present.
Light frost is expected and manageable. As it thickens, though, it blocks airflow through the coil and reduces heat transfer, making it harder for the system to pull warmth from outdoor air. Defrost removes that buildup before it becomes a real performance problem.
What Happens During a Defrost Cycle
During defrost, the heat pump temporarily reverses refrigerant flow. The reversing valve (the component that switches the system between heating and cooling) sends warm refrigerant through the outdoor coil to melt accumulated frost and ice.
Many systems use demand defrost, which relies on a coil temperature sensor and system conditions to determine when frost removal is needed. Others use time-temperature defrost, which checks both elapsed run time and coil temperature before starting a cycle. Either way, the process is automatic and controlled by the equipment itself.
The outdoor fan commonly stops while the coil warms. You may hear a whooshing sound, see steam, notice water dripping beneath the unit, or feel a brief change in indoor airflow. Systems with auxiliary heat may use it during defrost to keep indoor comfort steady.
What’s Normal During a Cold Snap
Most defrost cycles last between 5 and 15 minutes, though the exact timing depends on the equipment, the amount of frost, and conditions outside. After the frost clears, the system returns to normal heating. Cycles may happen more frequently during wet snow, freezing mist, or humid air near the freezing mark because those conditions supply more moisture for frost formation. Dry continental cold can be bitter without producing the same level of coil buildup.
Signs that are usually normal:
- Brief steam: Water vapor rises from the outdoor unit as melted frost meets cold air.
- Temporary fan pause: The outdoor fan stops while warm refrigerant clears the coil.
- Water beneath the unit: Melted frost has to drain somewhere after a completed cycle.
- Short comfort change: Indoor air may feel slightly less warm for a few minutes while the system transitions back to heating mode.
When Defrost Behavior Signals a Problem
Defrost itself is normal, but a unit that stays encased in ice after completing a cycle isn’t. Repeatedly long defrost periods, frequent cycling with little recovery time, worsening indoor comfort, or a heat pump that never seems to leave defrost are all worth an evaluation.
Several issues can interfere with normal frost removal: debris or snow blocking airflow, a dirty coil, a fan problem, a sensor or control fault, or refrigerant-related performance issues. The symptoms alone don’t point to a single cause, which is why an inspection is more useful than guessing.
Also listen for sounds beyond the normal whoosh and fan pause. Scraping, grinding, banging, or sustained mechanical noise isn’t part of a typical defrost cycle and can indicate a separate equipment concern that needs attention sooner rather than later.
How to Support Your Heat Pump Before & During a Cold Snap
You can support normal operation without trying to force defrost manually. The goal is straightforward: preserve airflow around the outdoor unit, allow melted water to drain, and track changes that help a technician understand what the system is doing.
Before and during freezing weather:
- Keep the area clear: Remove leaves, snowdrifts, vegetation, and other obstructions from around the outdoor unit without bending coil fins or reaching into the equipment.
- Watch drainage: Make sure meltwater can leave the unit freely instead of refreezing around its base.
- Observe the thermostat: Note any alerts, unusual temperature swings, or extended auxiliary heat use.
- Track the pattern: Record approximate defrost duration, visible ice buildup, and whether indoor temperatures recover afterward.
- Avoid unsafe shortcuts: Don’t chip at ice, pour hot water over the unit, cover it tightly, or repeatedly raise the thermostat to interrupt normal operation.
Seasonal heat pump maintenance scheduled before winter can help identify dirty coils, airflow restrictions, sensor issues, and other conditions that affect defrost performance. It won’t eliminate normal cold-weather defrosting, but it can help the system complete those cycles the way it’s supposed to.
Persistent Ice After Defrost Isn’t Something to Wait Out
If your heat pump stays iced over, loses heat for extended periods, or keeps cycling without recovering, that’s worth addressing before the next cold stretch arrives. At Sturm, we’ve been providing honest, professional heat pump service to Greater Spokane homeowners since 1945. If your system’s defrost behavior seems off, reach us at (509) 215-9429 to talk through what you’re seeing.