Heat Pump Blowing Cold Air?
Heat pump blowing cold air in heat mode? It's often a normal defrost cycle. Learn how to tell, what to check first and when to call for a repair.
Key takeaways
- Cold air for 5 to 15 minutes is usually a normal defrost cycle.
- Defrost runs more on damp, near-freezing mornings, common in the Upstate.
- Check the thermostat mode, fan setting, filter and outdoor unit first.
- Cold air past 15 minutes or an iced-over unit means it's time to call.
A heat pump blowing cold air in heat mode is usually in a defrost cycle. It pauses heating for a few minutes to melt frost off the outdoor unit, then warm air comes back. If the air stays cold for longer than about 15 minutes, something else is wrong.
Here is how to tell normal from not normal, what you can safely check yourself, and when it's time to call a technician.
Is it normal for a heat pump to blow cold air in heat mode?
For a few minutes at a time, yes. On cold days, frost builds up on the outdoor coil. To clear it, the heat pump briefly runs in reverse and pulls heat from inside your home to warm the coil.
Lennox says a typical heat pump defrost cycle lasts 5 to 15 minutes, and the system checks for frost every 30 to 90 minutes while it's heating. During defrost you may notice:
- Cool or lukewarm air from the vents
- Steam rising from the outdoor unit (that's melting frost, not smoke)
- A whoosh as the system switches modes
- The outdoor fan stopping for a few minutes
There's a second reason heat pump air can feel cool. A heat pump delivers a steady flow of warm air rather than the blast of hot air a gas furnace makes. Hold your hand to the vent and it may feel only lukewarm, even while the house is warming up. If your rooms reach the temperature you set, the system is doing its job.
Why does my heat pump blow cold air more on damp winter mornings?
Frost needs cold air and moisture. Lennox notes that defrost cycles run more often on cold, damp days and rarely on dry or sunny ones.
That's a common pattern in Greenwood and the Upstate. Winter mornings are often damp and hover near freezing, then warm up by the afternoon. Expect more defrost cycles early in the day, and fewer once the sun is out.
What should I check before I call?
Most fixes you can safely do take five minutes. Work through these in order:
- Wait 15 minutes. If it's a defrost cycle, warm air comes back on its own.
- Check the thermostat mode. It should say HEAT, not COOL or OFF. If you recently replaced or reprogrammed your thermostat, a wrong setting is a common cause.
- Set the fan to AUTO. With the fan on ON, it keeps blowing between heating cycles and during defrost, which feels like cold air.
- Check the air filter. A clogged filter chokes airflow. ENERGY STAR recommends you inspect, clean or change your filter once a month and notes that airflow problems can cut efficiency by up to 15 percent.
- Look at the outdoor unit. Clear away leaves, pine straw or snow, and make sure nothing is stacked against it. Don't chip ice off the coil, which can bend the fins.
- Check the breakers. The indoor and outdoor units each have a breaker. If one has tripped, reset it once. If it trips again, leave it off and call for service.
What causes a heat pump to keep blowing cold air?
If the air stays cold after those checks, one of these is the likely cause:
| What you notice | Likely cause | What to do |
|---|---|---|
| Cold air nonstop, outdoor unit not running | Tripped breaker, failed capacitor or contactor | Reset the breaker once, then call |
| Outdoor unit covered in thick ice | Defrost control, sensor or airflow problem | Turn it off and call |
| Defrosts again and again, for longer each time | Dirty coil, faulty sensor or low refrigerant | Schedule a repair visit |
| Air is cool and the house never warms up | Low refrigerant or a reversing valve problem | Schedule a repair visit |
| Weak airflow from every vent | Clogged filter, blocked return or blower problem | Change the filter, then call if it continues |
Low refrigerant always means a leak somewhere, because a heat pump doesn't use up refrigerant. A technician needs to find and fix the leak, not just top it off.
When should I call a pro?
Call a technician if the air stays cold for more than about 15 minutes, the outdoor unit is iced over, a breaker keeps tripping, or you hear grinding or loud buzzing from either unit.
Higgins Heating & Cooling handles heat pump and HVAC repair across Greenwood, Greenville and the Upstate. To catch defrost and refrigerant problems before winter, the Higgins Club maintenance plan includes a spring and fall tune-up and priority scheduling. Getting a big repair quote? Check our current offers, including a free second opinion.
Frequently asked questions
Should I switch my thermostat to emergency heat?
Only if your heat pump has stopped heating and you are waiting on a repair. Emergency heat skips the outdoor unit and runs only the backup heat strips, which costs a lot more to run. Don't use it to get through a normal defrost cycle. Switch back to HEAT once the system is fixed.
Should I turn my heat pump off when it goes into defrost?
No. Defrost is how the system keeps the outdoor coil working on cold, damp days. Turning it off in the middle of a cycle can leave ice on the coil. Let it finish. Warm air should come back within about 15 minutes.
Is it bad if my outdoor unit has some frost on it?
A light coat of frost on a cold morning is normal, and the defrost cycle clears it. A unit covered in thick ice, or one that stays iced over all day, is not normal. Turn it off, keep it clear of snow and dripping gutters, and call for service.
How often should a heat pump be serviced?
Once a year at minimum. ENERGY STAR suggests having the heating system checked in the fall before contractors get busy. A heat pump heats and cools, so many homeowners book a visit in both spring and fall.
The bottom line
A heat pump blowing cold air for a few minutes on a damp morning is almost always defrost mode, and it fixes itself. Check the thermostat, fan setting, filter and outdoor unit first. If the air is still cold after 15 minutes, schedule a heat pump repair so you get a warm house without the guessing.
