If the recent heat surges are anything to go by, this summer is bound to be one of the hottest in recent years. This means your air conditioner will need to come through now more than ever. And if your AC is on but your house is not cooling, then you are in for a long and stressful summer.

Fortunately troubleshooting and fixing most of the underlying issues is easier then you think. Keep reading to learn how to fix a malfunctioning AC.

How does an AC work?

To understand why your air conditioner is not cooling your house, you need to understand how an air conditioner works. The air conditioning system operates on a basic scientific process called phase conversion.

Essentially, refrigerant liquid undergoes a continuous cycle of evaporation and condensation within the unit’s sealed coil system.

The AC’s evaporative coils become icy cold as the refrigerant within turns from a liquid to a gas. Then the air conditioner’s fan blows air over those icy coils, which forces cooled air through your home’s ducting.

The gas then cycles back to a condenser coil unit and cools back down to a liquid and the cycle repeats itself over and over.

Why is my house so hot even with AC on?

Below are some reasons why your air conditioner is running but not lowering temperature;

The thermostat is set incorrectly

When you notice your home getting a little hotter than normal, first check the thermostat settings. Be sure it is set to cool. If the thermostat is set to cool, check the temperature setting to be sure someone hasn’t changed it.

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If it is off, set to heat, or set for constant fan (sometimes simply labeled “on”), switch it back to cooling operation. After the system kicks on, wait a few minutes, then check for cold air blowing from the registers. If it’s cold, problem solved! If not, move on to the next troubleshooting tip – checking the air filter.

Dirty air filter

Your AC system may include an air filter located in or around the indoor air handler unit. The filter catches dirt, dust and other airborne particles as they enter the air handler unit.

It keeps the components inside the system cleaner and operating more efficiently and can help keep the air in your home cleaner as well.

A dirty air filter can block airflow and reduce cooling to your home. In more extreme cases it can cause the system to shut down completely.

If your thermostat checks out and you still don’t have cool air, locate your system’s air filter, turn the system off, remove the filter and inspect.

If, after you are satisfied that you have a clean air filter and your central air conditioner does not cool your home, you’ll have to dig a little deeper to locate the problem.

The condenser unit is blocked

Most central air conditioning systems have an outdoor condenser unit. The exterior of the condenser unit features a large outdoor coil, which wraps most of the way around the outside of the unit. The coil includes a series of thin metal “fins” which are spaced very tightly together.

If your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil.

When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home. Dirt, grass and other airborne debris can accumulate between the fins, clogging the coil.

A dirty coil can lead to reduced energy efficiency, lack of cool air from the registers, or in extreme cases, complete system shutdown or damage to the compressor from overuse.

You can attempt to clean the coil by clearing away debris, carefully vacuuming the coil with a brush attachment or rinsing gently with a hose. If your system still isn’t cooling, it’s probably time to call a pro.

Damaged heat pump

In some cases, your outdoor unit might be a heat pump. A heat pump looks just like an AC unit, with some different components inside that allow it to both cool and heat your home.

In cooling operation, it operates just like an air conditioner system’s condenser unit and is subject to the same issues – dirty, clogged coil, frozen coil, refrigerant leaks, compressor malfunctions, etc.

If your heat pump system isn’t cooling, check thermostat settings, the air filter, and the condenser unit for previously described issues. If everything checks out and you’re still sweating inside, call your local HVAC dealer.

The evaporator coil is frozen

The indoor component of your central air conditioning system will include an evaporator coil. If your indoor unit is a furnace, the evaporator coil sits in its own cabinet, outside the furnace. If the indoor unit is a fan coil (typically as part of a heat pump system), the evaporator coil sits inside the fan coil cabinet.

Warm indoor air passes through the evaporator coil where heat energy and humidity are removed from the air. Cooler, more comfortable air is then circulated back to your home.

Signs of a frozen evaporator coil include:

• Frost forming on the copper refrigerant tubing coming from the coil cabinet
• Inadequate cooling
• Higher utility bills
• Excessive condensate drainage near your indoor unit
• In extreme cases, frost forming on exterior refrigerant tubing or the outdoor unit

Note: Because accessing the evaporator coil is difficult, resolving issues associated with a frozen evaporator coil are best handled by an HVAC professional.

Refrigerant leak

Refrigerant is a chemical that is critical to the cooling process. It flows through the system’s indoor and outdoor coil, changing from liquid to gaseous form, drawing heat energy and humidity from indoor air and releasing it outside.

Depending upon its severity, a refrigerant leak can contribute to your AC system not blowing cold air, your system may run for longer periods of time without adequately cooling your home, or it can cause a damaged or failed compressor and complete system shutdown.

Checking and resolving issues involving refrigerant levels in your system is another job for your local Carrier dealer.

Undersized air conditioner

Air conditioners are “sized” according to the amount of cooling they can provide as measured in BTUh (British Thermal Units per hour). Under moderate conditions, you may not notice any issues with an undersized air conditioner.

However, as temperatures rise outside, your AC may run for long periods of time and struggle to keep you cool.

You might be able to determine the size of your AC unit from the rating info on the cabinet panel, but it will be difficult to determine whether it is the “right size” for your home.

There are a number of factors involved in sizing a system for your home, including square footage, quality of construction and insulation, local climate, and more.

If your system is undersized, it may be possible to provide cooling in problem areas by adding a ductless unit to help out in “hot spots”. Or, it may be better to replace the system with one that is correctly sized.

The best way to address sizing issues is to contact a qualified HVAC professional who can accurately assess your home and its optimum cooling capacity.

Your home is drafty

If your home has more holes than a bagel factory, your air conditioner can struggle to keep up with the amount of warm air that’s sneaking in. Check for air leaks around windows, doors, and electrical outlets to locate any potential issues.

Leaking air ducts

Just as a leaky window or door can undercut your AC’s attempts to cool your home, leaky air ducts can also cancel out your air conditioner’s efforts. If your air ducts are leaky, all that chilled air that’s supposed to be carried into your home may be diverted to your attic instead.

Closed vents

Blocking your vents — whether intentionally or unintentionally — can make your air conditioner’s blower work overtime in order to move the air the extra distance to whatever vents are open. Increased pressure in the duct system and a blower that runs longer at a lower speed, which means it takes longer to drop the temperature indoors.

Low refrigerant level

Your AC needs refrigerant to run. Usually, you shouldn’t need to add any. Your air conditioner recirculates it. If you have a leak, however, you’ll need to schedule AC service by trained professionals.

How do I fix my home air conditioner that is not cooling?

Aside from checking AC coolant levels, there are a myriad of other solutions you can try to fix your malfunctioning AC. Below is a comprehensive list of things you can try;

Check and reset the thermostat.

It may seem simple, but sometimes when an air conditioner is working but not cooling it is simply the result of someone switching the thermostat from “Automatic” to “Fan.”

When the switch is set to “Automatic,” the thermostat switches on the air conditioning when the indoor temperature rises above the desired preset temperature. If the switch was accidentally set to “Fan,” the unit will blow air through the duct system, but no cooling will take place.

Replace the dirty filter.

If it’s been more than a couple of months since you’ve replaced the return-air filters in your AC system, they may be clogged, dirty, and affecting air flow. When filters get clogged with animal fur and dust, the AC system can’t draw in sufficient air, and as a result, only a wimpy flow of air comes out.

Clear the clogged condensation drain.

Air conditioners work in part by removing humidity from the air (through condensation), and that moisture must go somewhere. The job of a condensation drain hose is to direct water to a floor drain or to the outside of your home, depending on your system.

Condensation drains are subject to blockage by mold and algae growth. When this happens, some AC won’t blow cold air while others will shut down completely.

Note: Locate the end of the condensation drain line (it’s often in a utility room) and visually inspect it for clogs. If you see a clog, carefully clear it out with the end of a small screwdriver or similar narrow item.

If a clog forms higher in the line where you can’t physically reach it, suctioning on the end of the line will usually remove it. Use the hose on a wet/dry shop-type vacuum—and hold your hands around the opening—to create sufficient suction between the two hoses.

After removing a mold or algae clog, pour a couple of cups of white vinegar into the condensation pan that lies beneath the evaporator coils in the inside blower unit (learn how to access and identify the coils and the condensation pan below).

The vinegar will kill residual mold build-up and reduce the risk of future clogs.

Try to diagnose duct malfunctions.

In a central AC system, the main blower forces cold air through the ducting and into individual rooms. If a duct somewhere between the blower and a room register (the grill that covers the opening of an HVAC duct) has broken, the cold air could be blowing out before it reaches the room’s register.

If cool air is blowing from some registers but not from others, there’s a good chance the ducting that feeds the registers is at fault.

Note: If you have an unfinished basement, you can examine the ductwork to see if a joint has come loose. If so, refit the ends of the joint and tape the new joint securely with duct tape. If a ducting joint has come loose within a finished wall, however, you won’t be able to easily locate it and will need to call an HVAC professional.

Clear the area around the compressor.

If dry leaves and debris have piled up next to the compressor unit, it may not be able to draw in sufficient air. To find out, locate the compressor unit, which will typically be tucked away on the back or the side of the house where it won’t draw attention.

Note: Clean away all debris or anything else that might be crowding the unit, such as weeds or overgrown vines. For peak functioning, don’t place anything on top of the compressor.

Clean dirty coils.

If your air conditioner is working but not cooling, dirty coils may be the culprit. The typical AC system has two sets of coils: condenser coils, which are located in the outside compressor unit and evaporator coils, which are encased near the indoor blower unit.

When either set of coils becomes dirty or covered with mold and debris, cold air output can suffer. Cleaning the coils involves removing the metal enclosures that protect them.

Note: If you don’t feel comfortable opening the AC units you can ask a pro to clean them.

If you’d like to try cleaning the coils on your own, however, follow these steps:

Shut off the power to both the exterior and interior units at the breaker panel. Each one will be on a separate breaker.

Follow the AC manufacturer’s directions for removing the exterior compressor cage or the metal panels that house the evaporator coils.

To clean interior (evaporator) coils, spray a non-rinse evaporator coil cleaner such as Nu-Calgon Evap Foam No Rinse onto the coils, which resemble U-shaped copper or steel tubes.

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The non-rinse cleaner foams up on the coils and dissolves dirt and grime before liquefying and running into a condensation pan that empties into the condensation drain hose.

To clean exterior (condenser) coils, spray the coils, and the thin metal fins that surround them, with a condenser coil cleaner such as Nu Calgon’s Nu Blast Condenser Coil Cleaner. This cleaner is different from evaporator coil cleaner and it will require rinsing with the hose. Follow the product directions carefully.

Call a HVAC pro

If you’ve gone through the above DIY steps and your AC system is still not cooling, the problem could be leaking refrigerant (Freon) or a failed compressor unit. Freon is federally regulated and may only be handled by a licensed HVAC professional.

Note: If the AC not blowing cold air is the issue and your AC system is more than 10 years old, you may have a failed compressor and need to purchase a new system.

Should I turn off AC if it is not cooling?

Continuing to run an air conditioner with a refrigerant leak can eventually lead to a compressor breakdown–and since the compressor is the most vital part of your air conditioner this can mean premature system replacement.

So, if your air conditioner isn’t cooling, and you suspect a refrigerant leak, or if you’ve checked the air filter and thermostat to no avail, yes, you should shut your air conditioner off.