10 Reasons Why Your Air Conditioner Isn’t Working

worker servicing a room ac

It’s hard to keep a cool head when your air conditioner goes out, and the rest of your body is sweating from the heat. But instead of giving in to a complete meltdown, take some deep breaths and read through these reasons why your air conditioner isn’t working. If it’s a tripped circuit breaker, dirty air filters, or a thermostat setting issue, you may be able to DIY a quick fix, and get your system back up and running. For leaking refrigerant, a full drain pan, motor malfunction, or other reason, call in an HVAC technician to get your system right.

1. There’s a Tripped Circuit Breaker

If your air conditioning unit won’t turn on at all, the first thing you should check is your breaker box. If you see the circuit connected to your HVAC system has been tripped all the way to the off position, flip it back on; if it’s tripped in between the on and off positions, flip the switch all the way off, wait a few minutes, and then, put it back to the on position. 

Older homes built before the mid-1960s may have a fuse box, rather than a breaker box. The difference? Instead of simply flipping a tripped switch back into position, you’ll have to replace a blown fuse. Either way, these issues occur when your electrical system gets overloaded; tripping a circuit or blowing a fuse is the system’s way of protecting itself from complete damage.

Note: If your HVAC circuit breaker trips repeatedly, it could signify a more serious electrical issue and should be checked out by an expert. 

2. Your Air Filters Are Dirty

person cleaning ac filters
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When air filters are working properly, they’re not only preventing particles of dust, pollen, and other contaminants from entering your living spaces, but they’re also regulating airflow. Dirty air filters, on the other hand, reduce airflow because that air is blocked by the buildup of all those particles. 

Besides restricting cool air from entering areas of your home, clogged air filters can also indirectly cause your evaporator coil to freeze — literally — as the warm air in your house will be unable to travel to the refrigerant line that’s connected to the compressor in your outdoor AC unit. With no incoming air to cool, the refrigerant can end up freezing those coils instead, causing even more AC problems.

3. Refrigerant Is Leaking

If you have low refrigerant levels, usually because of a leak, your cooling system won’t be able to do its job. 

To put it simply, liquid refrigerant (or coolant, typically Freon or Puron) moves across the evaporator coil inside your indoor AC unit. The refrigerant absorbs hot air in your house, forms into a vapor, and then travels to the compressor located inside your outdoor unit. Compressed into a hot gas, it travels through the condenser coil to release heat outside. Finally, cooled by the expansion valve, it returns to the evaporator coil to absorb more indoor heat. 

You’ll know something’s wrong if you feel warm air coming from your vents or it’s taking too long for your air conditioner to cool down your house.

4. There Are Problems With Your Thermostat

Sometimes, all you may need to do is adjust your thermostat settings or change the batteries. For example, if your thermostat is running on fan-only, it’s simply blowing uncooled air around your home; if it’s set too high, the air conditioner won’t kick on.

Another common reason for thermostat issues? A blown fuse or debris inside the thermostat cover. Try removing it and clearing away any dust or replacing any fuses to see if that fixes things. If not, get help from an HVAC technician.

5. Those Condenser Coils Need Cleaning

The condenser, or outdoor unit of your air conditioner, can easily get dirty due to its location. This collection of dirt and debris will cause the system to use more energy than typically necessary to expel hot air and produce cool air, potentially tripping the circuit breaker and shutting the system down. To avoid this, be sure to schedule regular maintenance and cleaning of your HVAC system twice a year.

6. Your Drain Pan is Full

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We’ve already talked about how your air conditioning unit removes warm air from your home and releases it outdoors, but this unit also sucks out all the humidity in your space, too. This liquified moisture collects in the drain pan and is supposed to empty outside via the drain line.

If dust, dirt, mold, and other contaminants are allowed to build up in the drain line, though, it becomes impossible for that liquid to escape the drain pan, and as more and more moisture is removed from the air, more and more liquid is gathering in the pan.

After reaching a certain threshold, the high level of water will trigger the float switch and shut off the AC unit to prevent overflow and protect your home from water damage. An HVAC professional can remedy this issue and get your air conditioner working again.

7. A Capacitor Has Failed

The start capacitor gives your AC unit the extra jolt it needs to cut on, while the run capacitor maintains the energy needed to keep the air conditioner, well, running. Most often, the run capacitor is the one to give out, and it typically does so because of overheating or old age — a capacitor’s lifespan is around five to seven years.

Capacitors stay charged with electricity, so it’s not recommended that homeowners attempt a DIY replacement. Instead, leave that up to the pros.

8. Your AC System Is the Wrong Size

If buying a new air conditioning unit on your own, it’s best to first consult with an HVAC professional for guidance on determining the appropriate size for your home. Things you’ll need to consider include:

  • House size
  • Number of windows
  • Natural shade
  • Cooling capacity
  • Local climate
  • Insulation

If your unit is too small, it’ll have a hard time efficiently cooling your home and will end up consuming too much energy in its attempt to do so. If it’s too large, it will shut off and on way too often, impeding its ability to remove moisture from the air while also wearing itself out more quickly than it should.

9. An AC Fan Motor is Malfunctioning

Your central air system has two motors: the inside blower motor and the outside condenser fan motor. The blower motor sends cool air throughout your home, while the condenser motor expels the hot air taken from your home into the outdoors.

When one or both of those AC fans goes on the fritz, you’ll experience:

  • Restricted airflow
  • Uneven cooling
  • A grinding or clicking sound when unit turns on
  • Excess energy use/higher utility bills

10. There’s Been a Lack of Regular Maintenance

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As they say, “an ounce of prevention is worth a pound of cure,” and a regular HVAC tune-up can definitely help you save money by finding and fixing issues before things are too far gone. If you skip out on regular maintenance, though, a few consequences may include:

  • Costly AC repairs
  • Inability to cool properly
  • Dirty AC unit parts
  • Shortened HVAC lifespan
  • Higher electricity bills
  • Lessened energy efficiency

FAQ About Why Your Air Conditioner Isn’t Working

Why is my window AC unit not working?

A few reasons why your window AC unit may not be cooling your rooms efficiently:

  • It wasn’t installed correctly and may not be level/securely set inside the window.
  • It’s not sealed properly with weatherstripping, so there are air leaks. These leaks can let in warm air and let out cooled air, affecting the function of your AC unit.
  • It’s located in a window that receives direct sunlight, meaning it has to output excess energy to cool your rooms.

Should I shut off my air conditioner if it’s not cooling?

Yes. While the air conditioner may technically be running, it’s not cooling and only blowing out warm air. Keeping it on despite this will only:

  • Worsen the problem/cause greater damage
  • Potentially lead to overheating
  • Waste energy

It’s best to shut off the air conditioning system completely until an HVAC technician can get to your home, diagnose the problem, and make any necessary repairs.

What is a ductless HVAC?

Just as its name suggests, a ductless HVAC is a heating and cooling system that works without a network of passageways installed inside your home. Synonymous with the terms “mini-split” and “ductless heat pump,” this system focuses on regulating the temperature of an individual living space. In winter, the system provides heat to the room; come summer, you can flip the reverse switch to put it in AC mode.

Rather than air ducts, each mini-split is connected to an outdoor condenser via a refrigerant line.

When to Hire a Professional

Thermostat suddenly go blank? AC only blowing hot air? Notice uneven cooling in different rooms? It’s safe to say you’ve got yourself an air conditioning problem. Some of these issues may be able to be fixed on your own — like changing thermostat settings or batteries, cleaning or replacing dirty air filters, or resetting a tripped circuit breaker. 

But, if the problem is more serious and/or involves doing any kind of electrical work, it’s best to get the assistance of an HVAC pro near you. Beyond them finding and fixing the immediate problem, they’ll also be able to schedule regular maintenance visits to avoid any issues in the future. As part of the twice-yearly maintenance, these pros will clean and inspect your HVAC components, lubricate any parts as needed, and ensure all safety measures are working properly. And you? You can feel confident that every room in your home will stay comfy no matter the season.

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Andréa Butler

Andréa Butler is a writer and editor. And while she hasn't been blessed with DIY skills herself, she is adept at writing and enjoys sharing home improvement tips and pool care guides for the true DIYers out there.