Why Is My Heat Pump Blowing Cold Air?

Last updated: October 2026

If your heat pump blows cool air for 5 to 15 minutes and then goes back to heating, it’s almost always a normal defrost cycle, according to Lennox. If it blows cold air for longer, or all the time, the usual causes are the wrong thermostat setting, a stuck reversing valve, low refrigerant, a failed defrost control, backup heat that isn’t working or restricted airflow.

Heat pump still blowing cold air? AVS provides 24/7 heat pump repair across Northern Virginia and Maryland, with no extra charge for evenings, weekends or holidays. Call 703-457-9028 (VA) or 301-686-7129 (MD).

Is your heat pump in defrost mode?

In heating mode, a heat pump pulls heat from the outdoor air. That makes the outdoor coil very cold, and moisture in the air can freeze on it. To clear the frost, the heat pump briefly reverses and runs like an air conditioner to warm the outdoor coil.

According to Lennox, this defrost cycle usually lasts 5 to 15 minutes, and the system blows cooler air while it runs. Today’s Homeowner adds that during frigid periods, defrost can happen every 30 to 90 minutes.

Defrost doesn’t only happen on the coldest days. Lennox notes that homeowners are often surprised to see a heat pump defrost when the outdoor temperature is in the 40s, because damp air freezes on the coil more easily. That’s common in Northern Virginia, where winter brings frequent freeze-thaw swings and humid cold.

Signs it’s defrost mode:

• The cool air lasts a few minutes, then heat returns on its own
• The outdoor unit gets louder for a short time
• The outdoor fan stops while the unit defrosts
• The indoor blower slows or pauses briefly

Many systems turn on backup electric heat strips during defrost to warm the air before it reaches your rooms, as James River Air Conditioning explains. If defrost ends within about 15 minutes and heat returns, your heat pump is working correctly.

Is the air actually cold, or just cooler than a furnace?

Some “cold air” isn’t a problem at all. Carrier points out that air from a heat pump register may naturally feel cooler than the intense heat from a gas furnace.

Outdoor temperature matters too. Lennox explains that heat pumps become less efficient as the temperature falls, so in very cold weather the air coming out can feel less warm than you expect.

Many Northern Virginia homes handle this with a dual-fuel system. Leonard Splaine describes this setup as a heat pump paired with a gas furnace, where the heat pump heats efficiently in mild weather and the furnace takes over on the coldest nights.

3 checks to do before you call

1. Check the thermostat. Make sure it’s set to “heat,” not “cool” or “fan.” Lennox suggests raising the setting by at least 5 degrees and listening for the system to start.
2. Check the air filter. If you can’t see light through it, replace it. A clogged filter restricts airflow and can make the air feel cooler.
3. Check the outdoor unit and breaker. Clear snow, leaves and debris from around the outdoor unit, and make sure the breaker for the heat pump hasn’t tripped.

If you still have cold air after these checks and it isn’t a short defrost cycle, one of the causes below is likely.

What your symptom is telling you

Common causes of a heat pump blowing cold air

1. Thermostat settings, or a new thermostat set up wrong

Carrier lists an incorrect thermostat setting as one of the most common causes of a heat pump not heating. If the thermostat is on “cool” or the fan is set to run constantly, you’ll feel cool air.

A new thermostat can cause the same problem. Heat pumps use a reversing valve wire, labeled O or B, to switch between heating and cooling. If the thermostat’s O/B setting doesn’t match your heat pump, the system will cool when you ask it to heat. Amazon’s smart thermostat support page, for example, tells heat pump owners to flip the reversing valve setting from O to B or B to O when heat and cool are reversed. If you recently replaced your thermostat, have the O/B setting checked first.

2. Stuck reversing valve

The reversing valve switches the direction of refrigerant so the same equipment can heat or cool. Carrier notes that if your heat pump works perfectly in cooling mode but won’t heat, the reversing valve may be stuck. Because the valve is part of the sealed refrigerant system, replacing it is a job for an HVAC technician.

3. Low refrigerant or a leak

A heat pump needs the right amount of refrigerant to absorb heat outside and release it indoors. James River Air Conditioning explains that a leak severely reduces that ability, leaving lukewarm or noticeably cool air at the vents. Low refrigerant means there’s a leak that needs to be found and repaired.

4. Frozen outdoor unit or a defrost control problem

Light frost is normal. A unit encased in thick ice is not. Today’s Homeowner advises calling a professional if the heat pump seems to be in defrost continually or stays covered in ice even after defrost runs, because something is likely malfunctioning. Coastline Heating & Air sets a simple rule of thumb: call a technician if the system spends more than 15 minutes in defrost or defrosts more often than every 30 minutes. For more on this problem, see why a heat pump freezes up.

5. Backup heat strips not working

Many heat pumps rely on electric heat strips in the indoor air handler for extra heat during defrost and on very cold days. If those strips fail, the air during defrost can feel very cold, and the house may struggle to stay warm in a cold snap. Dr HVAC notes that cold air lasting beyond 15 minutes can point to a refrigerant leak or a malfunctioning auxiliary heat strip.

6. Dirty filter or restricted airflow

Lennox explains that a clogged filter restricts airflow, making it harder for the heat pump to heat your home, so you may notice cooler air. Johnson’s Polar Air also lists a dirty coil among the causes of a heat pump blowing cold air on heat mode.

7. Tripped breaker or outdoor unit not running

Carrier names a tripped circuit breaker as one of the most common causes of a heat pump not heating. If the indoor fan runs but the outdoor unit is silent, no heat is being moved into your home, so the air feels cold. Reset the breaker once. If it trips again, call a technician.

Should you switch your heat pump to emergency heat?

Emergency heat shuts off the outdoor unit and heats your home using backup heat only. It’s meant for short-term use while you wait for a repair.

Southwest Cooling & Heating advises switching to emergency heat if the system has blown cold air continuously for more than 30 minutes or the outdoor unit is encased in a solid block of thick ice, because it shuts down the outdoor unit and helps prevent compressor damage. Backup heat costs more to run than the heat pump alone, so switch back once the problem is fixed.

What do heat pump repairs cost?

Repair costs depend on the part that failed, from a thermostat setting to a reversing valve or refrigerant leak. For typical prices, see our guide to heat pump repair costs.

When to call for heat pump repair

Call a technician if:

• Cold air lasts more than 15 minutes at a time
• The system defrosts more often than every 30 minutes
• The outdoor unit is covered in thick ice
• You hear hissing, grinding or loud clicking
• The breaker trips a second time
• Heating fails but cooling works

AVS provides 24/7 heat pump repair across Northern Virginia and Maryland, with same-day service and no extra charge for evenings, weekends or holidays. Site visits start at $90.

Why Northern Virginia and Maryland homeowners call AVS

• Founded in 1991, with more than 50,000 residential and commercial customers served across the Washington DC metro area
• 24/7 service, 365 days a year, with no extra charge for evenings, weekends or holidays
• Service for all major heat pump brands, including Trane and Carrier
• Licensed in Virginia (HVAC 2705039269A) and Maryland (HVAC 520714137895, Home Improvement 4192876)
• Call 703-457-9028 (VA) or 301-686-7129 (MD)

Frequently Asked Questions

How often should a heat pump be serviced?

Twice a year. Lennox recommends a professional inspection once before the heating season and once before the cooling season, and Johnson’s Polar Air gives the same advice for heat pumps in Virginia. A heat pump both heats and cools, so unlike a furnace or AC alone, it runs through every season. AVS offers heat pump maintenance across Northern Virginia and Maryland.

Why is my heat pump steaming in winter?

Steam rising from the outdoor unit is usually a sign the defrost cycle is working. When the unit warms its outdoor coil to melt frost, the water turns to vapor in the cold air, as Coastline Heating & Air explains. Steam is normal. Smoke, a burning smell or steam that never stops is not, and needs a technician.

What does “AUX” or “auxiliary heat” mean on my thermostat?

Auxiliary heat is your heat pump’s backup heat, usually electric heat strips in the indoor unit. According to James River Air Conditioning, these strips kick on automatically during a defrost cycle to warm the air. Seeing “AUX” now and then on cold days is normal. If it shows constantly, have the system checked.

Is my heat pump broken if the house is a few degrees below the setting?

Not necessarily. Heat pumps heat more gradually than furnaces, especially on very cold days. Carrier suggests having the thermostat and system checked if the indoor temperature is consistently more than 2 to 3 degrees away from the thermostat setting. A gap of a degree or two on the coldest nights can be normal.

Is it normal for a heat pump to run constantly in winter?

Yes, in cold weather it usually is. Go Green Plumbing, Heating & Air explains that heat pumps move heat gradually, so they run longer cycles and more often when it’s cold. BPM Heating, Cooling & Plumbing in Frederick, Maryland, notes that nonstop running is normal once temperatures fall below freezing. It’s only a concern if the house still won’t warm up.

What temperature should the air from my heat pump vents be?

Warm, but not as hot as a furnace. Allied Air & Heat says heat pump air usually comes out around 90 to 100 degrees, compared with about 120 degrees from a gas furnace. It should still feel warm to your hand. If the air feels ice cold, the heat pump or its backup heat strips may need repair.