Reviewed by PRO MAX HVAC & Appliance Repair technicians, EPA 608 certified
A heat pump outdoor fan not running for a few minutes on a cold morning is usually a normal defrost cycle, and the fan restarts on its own. A fan that stays still while the compressor keeps humming, and a coil that keeps icing up, means the fan has failed, most often at the motor or its capacitor. Switch the thermostat to emergency heat to protect the compressor and call a technician.
The stakes are mostly on your bill. The U.S. Department of Energy estimates that a heat pump can cut the electricity used for heating by about 50 percent compared with electric resistance heat. Emergency heat is electric resistance heat, so it keeps the house warm while you wait for a repair, but every day on it costs noticeably more than normal heat pump operation.
Is It Defrost or a Failure?
Defrost is the first thing to rule out, because it looks alarming and is completely normal. In heat mode, the outdoor coil runs colder than the outside air. On damp Sacramento-area mornings in the low 40s, frost forms on it. Every so often the heat pump reverses for a few minutes to warm the coil and melt that frost. During defrost the outdoor fan shuts off on purpose, so the heat stays on the coil.
You will usually see steam rising from the top grille, hear a whoosh when the cycle starts and ends, and feel cooler air inside for a few minutes. Then the fan starts again. Wait ten minutes before you decide anything.
When the Fan Has Actually Stopped
A fan that stays still for longer than ten minutes while the compressor hums has failed. Without the fan moving air, the outdoor coil cannot pull heat from outside, the coil freezes solid, and the compressor runs hot and hard.
The common causes are a failed fan motor, a weak or failed run capacitor that the motor needs to start, or a defrost control board that never tells the fan to restart. If nothing runs outside at all, fan or compressor, the contactor or the power feeding the outdoor side is the usual suspect instead. Leave the capacitor and wiring inside the electrical panel to a technician, because a capacitor holds a charge even with the power off.
Here is a typical first-cold-week call in Rancho Cordova. A 2014 heat pump runs normally in the afternoon, but each morning the house never warms up, and the outdoor coil is a block of ice by 8 a.m. The fan blades do not turn when the compressor starts. The fan capacitor has failed, and the motor cannot start without it. A new capacitor has the fan spinning and the ice clearing within the hour.
What You Can Check Safely
Look before you touch. A light white frost on the coil is normal. A coil packed with clear ice, or ice built up around the fan blades, is not. Leaves, a summer cover left on, or a shrub grown against the side also block airflow, so clear anything within about two feet of the outdoor side.
Look up, too. A gutter that drips onto the heat pump freezes into a sheet of ice on the top grille overnight. Fixing the gutter fixes that problem for good.
Do not chip at the ice with a tool or try to spin the fan blades by hand. Both damage the coil fins or the motor, and neither fixes the cause.
What to Do Until the Repair
Protect the compressor. If the fan is not running, switch the thermostat to emergency heat. On a heat pump with backup electric heat, that shuts the outdoor side off and heats the house with the strips. On a dual-fuel system, emergency heat runs the gas furnace instead. If your system has no backup heat, turn it off, keep doors and blinds closed to hold the warmth in, and book the earliest visit you can get.
Our view: a failed fan capacitor on a heat pump under about 12 years old is one of the most cost-effective repairs in HVAC, and it is almost always worth fixing the same day. Running the compressor for days with no fan is what turns a small repair into a large one. ENERGY STAR recommends regular professional maintenance for heating equipment, and a fall check catches a weak capacitor before the first cold week.
When to Call a Pro
Call when the outdoor fan stays still for more than ten minutes in heat mode, when the coil stays iced after a defrost cycle, when nothing runs outside at all even though the thermostat calls for heat, or when the heat pump makes a grinding or buzzing sound. Tell us whether the compressor hums; that one detail narrows the repair.
PRO MAX HVAC & Appliance Repair handles heat pump repair across the Sacramento area, including Rancho Cordova and Roseville. Call (916) 234-5925 or book through our online booking page.
Check a heat pump outdoor fan that is not running
Watch for a defrost cycle
Wait ten minutes; if you see steam rising and the fan restarts on its own, it was a normal defrost.
Look for ice and debris
Check whether the coil is lightly frosted or packed with ice, and whether leaves or a cover are blocking the top grille.
Listen to the compressor
If the compressor hums while the fan stays still for longer than ten minutes, the fan has stopped working.
Switch to emergency heat
Set the thermostat to emergency heat, or turn the system off, so the compressor does not keep running without the fan.
Call a technician
Book a visit for the fan motor, capacitor or defrost control rather than chipping at ice or opening the electrical panel.
Sources
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