Air Conditioner Not Cooling? Here’s What to Do

By Updated February 6, 2024

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An air conditioner not cooling your home properly can lead to discomfort, reduced air quality, and other issues. There are many reasons why your AC unit may fail to operate as intended, ranging from incorrect thermostat settings to it being the wrong size. Our guide looks at the most common causes of an AC unit not properly cooling your home and what you can do about each.

1. Incorrect Thermostat Settings

The simplest explanation for a non-cooling or improperly cooling AC unit is that your thermostat is set incorrectly. It might be programmed for a different season, or someone in your home has touched the component. Some modern thermostats can even automatically change settings. Just correcting its temperature settings is often enough to resolve the issue.

How to fix it: Ensure you have your thermostat settings switched to “Cool” and adjusted to a low enough temperature for your liking. This is an easy fix if the unit is set to “Heat” or “Off.” If only the fan is set to “On,” it might run continuously and even sound like the unit is on and operating normally. However, it won’t be cooling the air if only the fan is on.

Even if your thermostat settings are correct, there’s a chance that the thermostat panel itself has gone bad and will need replacing before it can properly communicate with your unit. A licensed HVAC professional can take a look and let you know if you have a broken thermostat, which is a relatively simple and cost-effective fix.

2. Dirty Air Filter

Most AC units will have one or more air filters near the system’s air intake vents designed to help filter out dust, dirt, pollen, and other allergens before the air circulates throughout a home. If these filters become dirty and clogged, your AC unit may have to work harder to take in air, affecting the system’s efficiency.

How to fix it: Issues caused by a dirty air filter are easy to fix and only require changing the filter. Here are some basic steps for changing a dirty air filter or multiple:

  1. Turn off your unit temporarily to ensure your safety.
  2. Locate your system’s air intake vents, which may be located in or around the unit’s indoor air handler and behind return vents throughout your home.
  3. Remove vents or covers to access the clogged filters. You may need a screwdriver for this step.
  4. Confirm the filter size in place and swap it out with a new filter of the same size.
  5. Ensure that the new filter is positioned correctly according to the airflow direction. This will be marked on the side of the filter with an arrow.
  6. Replace the access door, vent, or filter cover.
  7. Turn your AC unit back on.

3. Blocked Condenser Unit

The outdoor portion of your AC unit contains a condenser coil. This draws heat out of your home and releases it outside, which helps to cool the air indoors. If the unit or its coils are blocked with dirt, grass, or other debris buildup, you may find that your home isn’t cooling properly.

How to fix it: Visually inspect your condenser unit, checking through the grates to see if there are any obvious signs of debris or blockages on the outdoor coils. If you see any, you may be able to get rid of them with canned air, a vacuum attachment, or even by gently rinsing with your garden hose. It’s important not to disassemble your outdoor condenser unit in any way because you run the risk of electrocution. Leave any dismantling to the professionals.

4. Clogged Condensation Drain

One of the ways that your AC unit cools your home is by removing warm, moist air from your home and then cooling that air, which results in condensation. This condensation is collected and removed from your home by a drain, which can sometimes overflow or clog. If your condensation drain gets clogged, the unit could automatically shut off or lose efficiency while trying to cool your home.

How to fix it: The first step to checking and clearing a clogged condensation drain is to find its location. Your condensation drain hose or pipe may be found in a utility room, in your garage near an air handler, or might even be routed to the outdoor unit near your condenser. Once you locate it, check for issues. This could be standing water that hasn’t drained, a blockage at the end of the tube due to grass, dirt, algae, or mold, or even a bend in the hose. Most of these are quick fixes and involve clearing a drain, removing debris, or cleaning the pipe.

5. Dirty Coils

In addition to your outdoor condenser coils, your AC unit will have a second set inside your home called evaporator coils. These are typically located within the indoor blower unit and are responsible for pulling heat out of your home before it can be sent to the condenser coils outside and released.

These indoor coils can also get dirty, clogged, or coated in dust and mold over time. If and when this occurs, your unit’s efficiency will suffer, and your home might not be cooling properly.

How to fix it: You’ll likely need to remove a panel or casing to access your indoor evaporator coils. A coil guard may also be in place, designed to protect you and the fragile coils. Once accessed, you can clean these coils with compressed air, a special coil fin brush, or detergents. Many HVAC system manufacturers recommend having your coils cleaned by a professional so you don’t risk hurting yourself or damaging the system.

6. Frozen Evaporator Coil

Indoor evaporator coils can also freeze over in some circumstances, even on hot days. This can be due to airflow issues, dirty coils, low refrigerant levels, drainage problems, and extreme temperatures that cause the unit to overwork, which prevents it from adequately cooling additional air in your home. If you see frozen evaporator coils, you know there’s a problem.

How to fix it: You may have previously located your evaporator coils to check for dirt and debris, but if not, they’re usually in or near your indoor air handler. You may need to remove a cover or grate to reach them and check for freezing. If you see frozen coils or suspect some system component is frozen over, turn off your HVAC unit from the circuit breaker. This will give your system a chance to defrost and reset. If the system freezes over again once you restart the unit, it’s time to call a professional.

7. Damaged Ductwork

Even if your air conditioning unit is operating perfectly, you may still find that it’s not keeping your home cool if you have damaged ducts. The ductwork throughout your home pushes cooled air from your HVAC unit into different rooms. If it’s crushed or there is a hole, air may not flow properly, or cold air may escape into your attic space instead. The biggest sign that this is occurring is if the vents in certain rooms in your home are blowing cold air but not others.

How to fix it: If you suspect an issue with your ducts, climb into your attic space or go down to your basement and look at the ductwork. Be aware of the temperature, and also listen for the sounds of any escaping air. You’ll want to look for crushed air ducts, lines that have separated at the joint, or any visible holes. If you find damaged ductwork, you may be able to repair it with duct tape. Call a professional if you can’t find any obvious damage.

8. Leaking Refrigerant

Air conditioning systems use a refrigerant, usually freon, to cool air before pumping it back through a home. If your system leaks refrigerant, it may freeze over or simply fail to blow cold air as expected.

How to fix it: While handy homeowners can tackle certain troubleshooting and AC repair steps, you’ll need to call a professional if you suspect that you have a refrigerant leak. Freon is federally regulated, so this isn’t a repair you can handle on your own.

9. Damaged Compressor or Fan Motor

Another reason your HVAC system might be blowing out warm air or inadequately cooling your home is if you have a malfunctioning part. This might mean a damaged AC compressor unit, broken fan motor, or blown capacitor. Any of these failures can result in a system that freezes over or simply can’t keep your home at the proper temperature.

How to fix it: If you’re both handy and able to identify the problem, you may be able to fix or replace the part yourself. It could be as simple as hearing your air conditioner running but seeing that the condenser fan isn’t moving. However, for many homeowners, identifying a failed part will take the eyes of a professional.

10. Aging or Undersized Unit

In some cases, nothing might look broken. It could be that your unit is too small for your home and your family’s typical cooling needs or that it’s getting old and needs replacing. Like any mechanical system, an HVAC unit’s components will wear out over time and become more inefficient.

How to fix it: If a tune-up doesn’t solve the problem, replacing a too-small or too-old air conditioner unit is the only remedy. If your unit is a decade old or more and struggling to keep up with your usage, we suggest upgrading to a newer, more efficient model.

A professional will evaluate your home’s size and provide the best options for your cooling needs and budget. They can also provide you with a quote on how much a new unit will cost. According to our research, a new air conditioner installation costs between $3,800 to $7,500 without new ductwork.

Our Recommendation

The cost of a new air conditioner and installation is thousands of dollars, so troubleshooting and repairing your unit is always the best first course of action. If your AC unit isn’t blowing out cold air or adequately cooling your home the way it should, try hunting down and isolating the problem to see if it’s a quick fix. If you’re unable to identify the issue or aren’t comfortable messing with the components of the system, calling an HVAC technician is your next move. These professionals can accurately and safely diagnose the issue, offer solutions to get your system up and running, and cool your house down quickly.

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Air Conditioner Not Cooling FAQ

Should I turn off the AC if it’s not cooling?

Yes, if your AC unit isn’t cooling your home, you should turn off the system and let it rest. This will prevent it from overworking itself or freezing up and allow you to work through certain troubleshooting steps safely.

Why does my AC keep turning off?

If your home’s AC unit keeps turning off, it could be due to many issues and may even be a built-in fail-safe of the system. A system powering down could result from a tripped breaker or faulty thermostat switch or could be the unit’s way of preventing more damage from something like a blocked condenser drain.

What is the best way to cool down my house without an AC?

Depending on the weather outside, you can cool down your home without a working AC unit. You can close your shades, which helps limit the ambient heat entering your home and turn on any exhaust fans in your kitchen or bathrooms to draw out more heat. You can also consider using a u003ca href=u0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003eportable air conditioning unitu003c/au003e if you spend more time in one room than others.

How do I know if my AC unit is the right size for my home?

A good rule of thumb for determining whether your AC unit is the right size for your home is multiplying your home’s square footage by 20. That will give you the minimum u003ca href=u0022 target=u0022_blanku0022 rel=u0022noreferrer noopeneru0022u003eBtu (British thermal units)u003c/au003e needed, but you may require more or less depending on factors like ceiling height, doorway and window sizes, appliances in the home, level of shade, and even the number of windows in your space.