Heat Pump Not Cooling? 5 Causes & Quick Fixes (2026)

A heat pump not cooling your home in the middle of a summer heat wave is one of the most stressful HVAC problems a homeowner can face — mostly because people forget their heat pump isn’t just a heater. This guide is written for homeowners whose heat pump is running but the air coming out feels lukewarm, weak, or not cold at all, and who want to know what’s wrong before they pay for a service call.

By the end, you’ll know the five most common reasons a heat pump stops cooling, what it means when it blows warm air instead, which checks are safe to do yourself, and when the problem crosses the line into a same-day emergency.

The patterns below reflect what technicians actually see on hot-weather service calls — not a generic internet checklist. Let’s work through it step by step.

Why Your Heat Pump Is Also Your Air Conditioner

A heat pump doesn’t just make heat in winter — it moves heat. A component called the reversing valve flips the direction of refrigerant flow so the same outdoor and indoor coils that warm your house in January cool it in July. In cooling mode, your heat pump is functionally identical to a central air conditioner.

That’s important context: almost everything that causes a standard AC to underperform — a dirty filter, low refrigerant, a blocked outdoor unit — can also stop a heat pump from cooling. If your system has never cooled properly, or has recently stopped, it’s worth reviewing our broader guide to a heat pump not working for issues that affect both heating and cooling modes. If you’re comparing systems altogether, our heat pump vs air conditioner comparison and heat pump refrigerant guide cover the mechanical differences in more depth.

5 Common Reasons a Heat Pump Won’t Cool Your Home

Most cooling failures trace back to one of five causes. Working through them in order — cheapest and most likely first — will save you an unnecessary service call more often than not.

1. Dirty Air Filter or Frozen Indoor Coil

A clogged filter starves the system of airflow. Without enough air moving across the indoor coil, the coil gets too cold, ice forms on it, and cooling output drops sharply — sometimes to almost nothing. This is by far the single most common cause of weak or absent cooling, and it’s also the cheapest to fix.

2. Low Refrigerant Charge

Refrigerant doesn’t get “used up” — if the level is low, there’s a leak somewhere in the system. A low charge reduces the heat pump’s ability to absorb heat from your home, so air still blows but never gets truly cold. Low refrigerant needs a licensed technician; it isn’t a DIY fix and shouldn’t be treated like one. Refrigerant handling and system performance in Canada follow technical benchmarks set by bodies like ASHRAE, which is one reason this repair isn’t something to attempt without proper training and equipment.

3. Stuck Reversing Valve

If the reversing valve fails to switch, the system stays locked in heating mode even though the thermostat is calling for cooling — which is exactly why so many “heat pump not cooling” calls are actually reversing valve problems. This is a mechanical or electrical failure that requires a technician to diagnose and replace.

4. Blocked or Dirty Outdoor Unit

In cooling mode, the outdoor unit is where heat pulled from inside your home gets released. Grass clippings, leaves, mulch, or a fence built too close to the unit restrict airflow and make the whole system work harder while cooling less. This is one of the easiest issues for a homeowner to spot and fix.

5. Wrong Thermostat Mode or Settings

It sounds obvious, but it’s genuinely common — especially right after the seasons change or a power outage resets settings. If the thermostat is set to “Heat,” “Auto” with a confusing schedule, or a fan-only setting, the system may run without ever actually cooling. Always rule this out first; it costs nothing to check.

Symptom → Likely Cause Quick Reference

If you only have a minute, match what you’re seeing against the table below before reading further.

Still not sure which one matches your system? Answer a few quick questions and get a likely cause instantly:

Typical Repair Costs by Problem

These are rough Canadian ranges to set expectations — your heat pump repair cost guide has the full breakdown, and the heat pump cost calculator can give you a number specific to your situation.

Ranges reflect typical Canadian service call quotes and vary by region, brand, and technician. Confirm with a local diagnosis.

Heat Pump Blowing Warm Air Instead of Cool? Here's What It Means

Warm or room-temperature air from the vents during cooling mode usually means one of three things: the system is stuck in heating mode, it has lost refrigerant, or the reversing valve failed to switch. Which one it is often depends on when the air turns warm.

• Warm from the moment it turns on — usually a thermostat mode issue or a stuck reversing valve.
• Starts cool, then gradually warms up — often a refrigerant leak or a coil icing over from restricted airflow.
• Cool air, but weak airflow — points to a dirty filter or a failing blower motor rather than the refrigerant side at all.

Noting which pattern matches your system helps a technician diagnose the issue faster over the phone — and can save you a second visit.

More Heat Pump Cooling Symptoms, Explained

The five causes above cover most cases, but a few specific symptom combinations deserve their own explanation.

Heat Pump Running But Not Cooling

If both the indoor and outdoor units are running but the house still isn't cooling, the compressor is doing work without actually moving heat — the classic sign of a refrigerant leak or a reversing valve that hasn't fully switched. This isn't a DIY fix; it needs a gauge set and a technician.

Outdoor Unit Running, But No Cool Air Inside

This usually points indoors rather than outdoors — a dirty filter, a failing blower motor, or closed/blocked supply vents can all stop cool air from reaching the rooms even when the outdoor unit sounds perfectly normal.

Not Cooling After a Power Outage

A power outage can reset the thermostat to a default heating schedule or trip a breaker without you noticing. Always check the thermostat mode and the breaker panel first after any outage before assuming there's a mechanical fault.

Not Cooling Upstairs (But Fine Downstairs)

Heat rises, so upstairs rooms naturally run warmer — but a large gap usually means restricted airflow to those rooms specifically: closed vents, a clogged filter reducing overall output, or ductwork that was never balanced correctly for the second floor.

Cooling, But Not Cooling Enough

If the system cools but never quite reaches the setpoint on hot days, it may simply be undersized for your home, or it may be losing capacity from a slow refrigerant leak, dirty coils, or reduced airflow. A load calculation through the heat pump size & BTU calculator is a good first step.

Compressor Running, But Still Not Cooling

A compressor that runs continuously without producing cool air is working hard for no result — almost always a sign of low refrigerant, a failing compressor itself, or a reversing valve stuck between positions. Shut the system off and call a technician rather than letting it run.

DIY Checks Before You Call a Pro

These checks are safe for most homeowners and take less than fifteen minutes combined. If none of them solve the problem, it's time to call a technician rather than opening up the refrigerant lines yourself.

1. Confirm the thermostat mode. Set it to "Cool," not "Heat" or "Auto," and lower the temperature a few degrees below the current room temperature.
2. Check and replace the filter. A grey, dust-caked filter is often the entire problem — replace it if it hasn't been changed in the last 60–90 days.
3. Inspect the outdoor unit. Clear leaves, grass clippings, and debris, and make sure there's at least two feet of open space around it.
4. Look for ice on the indoor coil or lines. If you see frost or ice, turn the system off and let it thaw fully before running it again.
5. Check the breaker. A tripped breaker can let the indoor blower run while the outdoor compressor stays off, which feels exactly like "no cooling."

If you've worked through these and the system still isn't cooling, our heat pump troubleshooting wizard can help narrow down the issue further before you book a technician, and our seasonal AC maintenance checklist is worth bookmarking so this doesn't catch you off guard again next year.

When It Becomes a Summer Emergency

Most cooling problems can wait a day or two for a scheduled appointment. But during a heat wave, a home with no working cooling can become genuinely dangerous — particularly for infants, older adults, pregnant people, and anyone with a heart or respiratory condition.

Cooling failures become especially common during Ontario heat waves when outdoor temperatures push past 30°C, but the same urgency applies across the country — from dry Alberta summers to the humid, sticky heat that makes BC's Interior and Atlantic Canada feel hotter than the thermometer suggests.

Most HVAC companies prioritize no-cooling calls during heat waves, so don't hesitate to say it's urgent when you book — it usually gets you moved up the schedule.

Pre-Summer Tune-Up: Preventing This Next Year

Almost every cause on this list is easier and cheaper to catch during a spring tune-up than to fix mid-heat-wave. A yearly service visit before cooling season typically covers:

• Checking refrigerant charge and testing for slow leaks
• Confirming the reversing valve switches cleanly between modes
• Cleaning the indoor coil, outdoor coil, and blower components
• Calibrating the thermostat and testing both heating and cooling cycles
• Inspecting electrical connections and capacitors before they fail in peak heat

A properly maintained heat pump also runs more efficiently, which matters for a system that works year-round — see our full heat pump maintenance guide for a season-by-season checklist, and our heat pump lifespan guide if you're wondering how many more summers your current unit has left. For general efficiency benchmarks and what to look for in a well-maintained system, ENERGY STAR Canada is a reliable reference point, and homeowners considering an upgrade can check current federal incentives through the Canada Greener Homes Initiative.

Common Mistakes to Avoid

• Running the system with an iced-over coil — this can damage the compressor and turn a cheap fix into an expensive one.
• Assuming it needs a new unit — a heat pump problem is often a single failed part, not the whole system. If replacement does come up, the is a heat pump worth it quiz and heat pump cost calculator will tell you what a new install would actually cost before you decide.
• Skipping annual maintenance — this is the single biggest predictor of a mid-summer breakdown.
• Waiting out a heat wave with no cooling — treat prolonged extreme heat with no AC as a health risk, not an inconvenience.

Not sure if repair or replacement is the smarter call for your situation? This quick quiz will tell you:

Final Thoughts

A heat pump not cooling is almost always traceable to one of five things: a dirty filter, low refrigerant, a stuck reversing valve, a blocked outdoor unit, or a simple thermostat setting. Run through the quick DIY checks first — you'll solve the problem yourself more often than you'd think.

When the checks don't fix it, don't wait it out. A quick call to a licensed technician, especially during a heat wave, is worth far more than the cost of guessing.

Frequently Asked Questions