Problem guide
Why is my heat pump not cooling?
A heat pump that blows warm air in summer usually has one of a handful of causes. Some you can check in five minutes.
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Written by HYRE HVAC Research Desk Primary-source research, data analysis and fact checking
The short answer
A heat pump not cooling is most often a thermostat set to heat or auto, a clogged filter, a blocked or dirty outdoor coil, or a tripped breaker. Those you can check safely.
If they are fine, the likely causes are a failed capacitor or contactor, a stuck reversing valve, a frozen indoor coil or low refrigerant from a leak, and all of those need a licensed technician.
Check these first (safe DIY)
These steps need no tools and no access to wiring or refrigerant.
Confirm the mode (cool or heat), the setpoint (below room temperature for cooling, above for heating), the fan setting and the batteries if it uses them.
Pull the filter. If you cannot see light through it, replace it. A clogged filter starves the system of airflow. ENERGY STAR suggests checking it monthly in heavy-use seasons.
Is the fan spinning and the unit humming? Clear leaves, grass and anything stacked within a couple of feet. Do not open the panel.
If the breaker for the unit has tripped, switch it fully off, then on. If it trips again, leave it off: that is a fault for a technician, not something to keep resetting.
Ice on the refrigerant lines or the indoor coil means the coil froze. Set the system to off and the fan to on for a few hours to thaw it, then check the filter.
Likely causes and what they point to
| What you notice | Likely cause | Who fixes it |
|---|---|---|
| Warm air, outdoor unit silent | Tripped breaker, failed contactor or capacitor, thermostat wiring | Breaker: you, once. The rest: technician |
| Warm air, outdoor fan running | Stuck reversing valve, compressor not starting, low refrigerant | Technician |
| Weak airflow from vents | Clogged filter, frozen coil, blower problem | Filter: you. Blower: technician |
| Ice on lines or coil | Low airflow or low refrigerant | Thaw and change filter; recurring ice: technician |
| Cools but not enough on hot days | Dirty outdoor coil, undersized system, low charge | Technician |
Why do heat pumps have one extra failure point?
A heat pump is an air conditioner with a reversing valve that switches between heating and cooling.
If the valve sticks, or its solenoid or the signal from the thermostat fails, the system can heat when you asked it to cool.
That is why the first check is the thermostat mode, and why a technician will test the valve and its control circuit if the mode is right.
Heat pumps also run year round, so filters clog faster and outdoor coils collect more debris than on an AC that rests all winter.
When to stop and call
Do not open the outdoor unit, furnace cabinet or control box. Capacitors can hold a dangerous charge with the power off, and line-voltage work is for a licensed technician.
Adding refrigerant, finding leaks or even attaching gauges requires EPA Section 608 certification.
A repeat trip points to an electrical or compressor fault.
After a thaw and a new filter, recurring ice usually means a refrigerant or airflow fault.
What a technician will check
Expect a technician to measure voltage at the outdoor unit, test the capacitor and contactor, confirm the thermostat is sending the cooling signal, check the reversing valve, inspect the coils and measure airflow and refrigerant pressures.
A good diagnosis is written down: what was tested and what failed. If refrigerant is low, the next step is finding the leak, not just adding more. DOE’s 2018 field-study review found refrigerant charge faults in a large share of installed systems.
If the system is old and the fault is major, see repair vs replace. What drives the price of a repair is the part, refrigerant, access and labor; HyreHVAC publishes no prices yet, so use the repair cost calculator with your own quote.
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Questions
Why is my heat pump blowing warm air in cool mode?
Can a dirty filter stop a heat pump from cooling?
Should I add refrigerant to my heat pump?
How long should I let a frozen heat pump thaw?
Is a heat pump that will not cool an emergency?
Written and audited by
HYRE HVAC Research Desk
Primary-source research, data analysis and fact checking
We are a research desk, not a sales floor. We read the federal microdata file, the statute or the manufacturer data sheet ourselves, and we publish the figure with the document it came from and the date we retrieved it.
Where a number cannot be traced to a primary source, we publish the shorter page and say what we could not verify.
The counts below are generated from the published pages themselves, last counted October 26, 2026, and they are what we have actually published rather than what we intend to.
- 18
- studies published
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- federal sources read and cited
- 15
- studies published with their full dataset as CSV
- 51
- jurisdictions reproduced against EIA’s own tables
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Data as of Sources checked October 26, 2026. Authorship on this site is organizational: the analysis belongs to the desk rather than to a named individual, and we do not publish credentials we do not hold. Our editorial policy sets out how we source, date and correct what we publish.
Sources & retrieval dates
HyreHVAC is a publisher. We do not install, repair or inspect HVAC equipment and hold no contractor licence. Nothing here replaces an on-site diagnosis by a licensed contractor. Sources are cited with the date they were checked.