Why a heat pump freezes in summer
In cooling mode, the indoor coil (the evaporator) absorbs heat from your home’s air. The coil is cold, and moisture from the air condenses on it and drips away. If the coil gets too cold, or too little warm air moves across it, that moisture can freeze. Ice then blocks airflow even more, which makes the problem worse, and cooling drops.
Ice may show up on the indoor coil, on the larger copper line leading to the outdoor unit, or on the outdoor unit itself.
What to do right away
- Turn the system off at the thermostat. Switching the fan to On while the cooling is off can help the ice melt faster, if your system allows it (see heat pump fan: on or auto).
- Turn off power at the breaker if you can see significant ice or water, or if the unit has been behaving strangely.
- Do not chip or scrape the ice with tools. Coils and refrigerant lines are fragile and a puncture can mean a costly repair and a refrigerant leak.
- Let it thaw completely. This can take several hours, and sometimes longer for heavy ice. Do not restart the cooling until it has fully melted.
- Watch for water. Thawing produces water that can overflow a drain pan. Place towels or a container near the indoor unit if you can do so safely, away from electrical parts.
- Check the filter and replace it if dirty. Open all supply and return vents.
Common causes
Dirty filter and blocked airflow
A clogged filter, closed vents, blocked returns or furniture over registers can reduce airflow across the coil. This is the first thing to check and the easiest fix.
Dirty evaporator coil
Dust on the indoor coil acts like insulation and also restricts airflow. Cleaning the indoor coil usually requires opening the air handler, so it is typically a job for a technician.
Low refrigerant
A heat pump’s refrigerant circuit is sealed, so low refrigerant usually points to a leak. Low refrigerant can make the coil colder than it should be and cause ice. Adding refrigerant without finding and fixing the leak is not a lasting repair, and handling refrigerant requires proper certification. See how to tell if a heat pump is low on refrigerant for warning signs.
Blower problems
A failing blower motor, a dirty blower wheel or a faulty capacitor can reduce airflow. If the indoor fan is weak or not running, call a technician.
Cool outdoor temperature or very low set point
Running air conditioning when outdoor temperatures are fairly low, or setting the thermostat very low, can contribute to freezing in some systems. If you see ice only on unusually cool nights, try a higher set point.
Will it fix itself?
The ice may melt if you turn the system off, but the underlying cause will not go away. If a dirty filter was the cause and you replaced it, the problem might be resolved. If the ice returns, don’t keep restarting the system. Running a frozen system can stress the compressor, which is one of the most expensive parts to replace.
Winter frost vs. summer ice
Frost on the outdoor coil in cold weather is normal, since heat pumps have a defrost cycle that melts it. That is different from ice in the summer. The defrost mode can also produce vapor, which is why some owners wonder about steam coming from a heat pump. Summer ice on the indoor coil or line is not part of normal operation.
When to call a professional
- Ice returns after you replaced the filter and let everything thaw.
- You suspect a refrigerant leak (hissing, oily residue, weak cooling).
- The blower is not running or runs weakly.
- Water is leaking in the home.
- The system trips the breaker. Do not keep resetting it, see why heat pump breakers trip.
Preventing it
Change or clean filters regularly, keep returns and vents clear, keep the outdoor unit free of debris, and have the system serviced annually. For broader cooling issues, see our guide to a heat pump that won’t cool.
FAQ
What should I do if my heat pump freezes in summer? Turn it off, let it thaw fully, check the filter and vents, and call a professional if it freezes again.
Will a frozen AC fix itself? It will melt once the system is off, but the cause remains and the ice will likely come back.
Can I use a hair dryer to speed up thawing? Some sources suggest a low-heat hair dryer, but use caution around water and electrical parts. Turning off the system and waiting is the safer option.