Heat Pump Blowing Cold Air — Normal Defrost, a Thermostat Setting, or a Real Repair
Heat pump air feels cooler than a furnace, and a few minutes of cold during defrost is normal. Here's how to tell normal from broken, two checks to do first, and what each repair costs in the Valley.
The first cold morning of the year is when we get this call most. Half the time nothing is broken. The other half, a part that sat unused since March didn't wake up. Here's how to tell which one you have before you pay anyone.
First: is it actually cold, or just not hot?
A heat pump doesn't make air as hot as a gas furnace. Furnace air comes out of the register around 120° to 140°. Heat pump air comes out around 90° to 100°. Your hand is about 92°, so heat pump air can feel cool to the touch even when it's working perfectly.
The real test: hold a kitchen thermometer in a supply register for a minute. If it reads 25° or more above the room temperature, the heat pump is doing its job. If it reads within a few degrees of the room, something is wrong.
Normal cold air: the defrost cycle
On a cold morning, frost builds on the outdoor coil. Every 30 to 90 minutes the system runs a defrost cycle: it flips into cooling mode for a few minutes to melt it. You may hear a whoosh, see steam rising off the outdoor unit, and feel cool air inside for 2 to 10 minutes. Most systems turn on the heat strips during defrost to cover it, but not all do.
That's normal. Cold air that lasts longer than about 10 minutes is not.
Two checks before you call
- Thermostat set to Heat, not Auto or Cool, and the fan on Auto. With the fan set to On, the blower keeps running between heating cycles and pushes room-temperature air that feels cold. This one fix ends a lot of service calls.
- Look at the outdoor unit. Is the big fan on top spinning and the unit humming? If it's silent while the indoor blower runs, the outdoor unit isn't running at all: check the breaker and the disconnect box next to the unit. If it's buried in solid ice, skip to the causes below.
If you just had a new thermostat installed and it's blowing cold on Heat and cool on Cool, the O/B reversing valve setting is backwards. It's a one-menu fix in the thermostat's installer settings, and the most common problem we see after a DIY thermostat swap.
Real causes, most to least common
- Reversing valve stuck or its solenoid failed. The valve is what switches the unit from cooling to heating. It sat in cooling position since March. If the solenoid coil burned out or the valve sticks, the unit cools all winter. A solenoid coil is a cheap fix; a stuck valve is sealed-system work.
- Defrost control board or sensor failed. The system either can't come out of defrost (stuck blowing cold) or never goes into it (outdoor coil ices solid and heat output drops to nothing).
- Low refrigerant from a leak. A heat pump low on charge loses heat output first, because heating asks more of the refrigerant than cooling does. If it's low, it's leaking. We find the leak; we don't top it off.
- Outdoor fan motor or capacitor. No fan, no heat exchange, and the unit trips off on high pressure or ices over.
- Heat strips or sequencer dead. The strips cover defrost and very cold mornings. If they're out, defrost cycles feel freezing, and you'll notice it most before sunrise.
- Compressor not running. The indoor fan blows, the outdoor unit hums or clicks but the compressor doesn't start. Usually the capacitor first, the compressor second.
What the repairs cost
Installed, parts and labor, East Valley residential. These match our Tempe heat pump repair pricing.
| Thermostat O/B setting fixed | Diagnostic only | Or free if you find it yourself in the installer menu |
| Run capacitor | $165–$245 | The most common failure in any season |
| Reversing valve solenoid coil | $200–$400 | The cheap version of a reversing-valve problem |
| Defrost control board or sensor | $250–$600 | The usual "stuck in defrost" or "iced over" fix |
| Heat strip / sequencer | $200–$550 | Per element |
| Refrigerant leak search, repair and recharge | $500–$1,500 | R-410A. Recharge pricing |
| Reversing valve replacement | $900–$1,800 | Recover, braze, vacuum, recharge. Repair-vs-replace past 12 years |
| Compressor | $1,500–$3,000 | Compressor cost guide |
Anything over $1,000 on a system past 12 years gets both numbers on one sheet: the repair and the replacement. The tech doesn't earn commission on either.
Watch the electric bill
A heat pump that can't heat makes the thermostat lean on the electric heat strips. Strips cost three to four times more per hour of heat. If your thermostat shows "Aux" or "Emergency" heat most of the time, or your December SRP or APS bill jumps for no reason, the heat pump has a problem even if the house feels warm.
Why it happens in October and November
Your heat pump ran 2,500-plus hours this summer at 110°. The reversing valve, defrost board, and heat strips then sat unused until the first 40° morning asked them to work. A fall tune-up runs the system in heat mode, forces a defrost cycle, tests each heat strip, and checks the reversing valve before you need it. $59.95 per system, the same tune-up we run in spring. More on heating repair and maintenance.
Questions people ask
Why is my heat pump blowing cold air in heat mode?+
Most often it's a defrost cycle (normal for 2 to 10 minutes), the fan set to On instead of Auto, or a thermostat with the O/B setting backwards. If it's cold for more than 10 minutes with the thermostat set correctly, the usual causes are a stuck reversing valve, a failed defrost board, or low refrigerant.
Is it normal for heat pump air to feel cool?+
Yes. Heat pump air comes out around 90° to 100°, cooler than furnace air and close to skin temperature. If a thermometer in the register reads 25° or more above room temperature, it's working.
How long does a heat pump defrost cycle last?+
Usually 2 to 10 minutes, every 30 to 90 minutes on cold, damp mornings. Steam off the outdoor unit and a whooshing sound are normal.
Can I keep running a heat pump that's blowing cold?+
Not for long. If the outdoor unit is iced solid or the compressor is short-cycling, running it can damage the compressor. And if it's falling back on heat strips, it's costing three to four times as much to heat the house. Set it to Off and call.
What does it cost to fix a heat pump blowing cold air?+
Most fixes run $165 to $600: a capacitor, a reversing valve solenoid, a defrost board, or a heat strip. A full reversing valve replacement is $900 to $1,800, and a refrigerant leak repair with recharge is $500 to $1,500.