Informational Guide

Why is My AC Not Cooling?

If your air conditioning unit isn’t functioning properly, there are only a few causes. Let’s look at the common reasons ACs are no longer cooling a house.

by Josh M

AC can really be a lifesaver during those hot and humid months, but simply having one isn’t enough. There are times when air conditioning units have mishaps and don’t function properly, rendering it useless in cooling your home.

If you’re looking to fix yours, then look no further because we have everything you need to know!

The good news is that if your air conditioning unit isn’t functioning properly, there are really only a few causes it could be from. Let’s take a look at the most common to help determine, or at least narrow down what that may be in your case.

1. Thermostat Not Set Properly

This is probably the most obvious cause but is pretty easy to get wrong. Before anything else, check to see if your thermostat is set to cool. If it’s on “off” or “heat,” then there’s a chance you or someone else accidentally changed it.

Once the system is on, wait 5 minutes or so and go check for cool air coming out of the register. If it’s still not happening, we need to check the air filters and make sure they’re clean.

2. Refrigerant Leak

If your air conditioner is working but not cooling your house, it could be due to a refrigerant leak. As refrigerant runs through a closed-loop, you should never be low on it. If you do, then you definitely have a leak.

Refrigerant leaks vary in severity, and if you suspect this is the case, you should seek help from a pro sooner rather than later. If it’s a serious leak, it could result in a damaged/failed compressor which can cause an entire shutdown of the unit.

3. Leaking Air

If the ducts are leaking, this can result in unconditioned air making its way in, raising the temperature of the air the AC unit pushes out. These are difficult to detect, but if your energy bills are more than usual or if certain rooms are difficult to cool, then it’s likely. You’ll want to contact a professional in this case.

4. Problem with the Condenser

It’s possible that the air conditioner condenser is blocked. This can happen when dirt, grass, and other stuff gets built up between the fins. This can result in lowered efficiency, less cool air coming out, or even an entire shutdown of the system! If you notice any debris, try to clean it out with a hose or brush attachment.

5. Frozen or Dirty Evaporator Coils

The evaporator coils may be dirty or frozen. If you see that your evaporator coil has frost developing on the copper tubing or that your utility bills are higher than average, it’s very possible they’re frozen. In this case, it’s usually better to call up an HVAC pro instead of attempting to fix it yourself.

6. Damaged Compressor

Compressors are the priciest component of AC units, and if it ends up damaged it’s usually caused due to consistent use over long periods of time. You can get a professional to fix it in many cases, but sometimes you’ll have to get it replaced.

7. Thermostat Issues

It could be that your thermostat is inaccurately measuring the temperature of the air inside your home. This could lead to it adjusting the cooling improperly as well. Not only that, but it could simply be a problem with the settings, as we mentioned earlier.

Check to see if it needs batteries, and replace them if so. If the batteries are good, do a quick restart of the system.

8. Damaged Heat Pump

Some AC units are actually heat pumps (though not all are, so find this out first). If the heat pump system isn’t providing cool air, check the thermostat settings, air filter, and condenser unit.

9. Undersized Air Conditioner

It is possible that your AC unit is simply too small for your home! In order to discover the right size for your home, check the rating info on the cabinet panel. Consider the square footage of your home, the insulation it has, the climate in your area, and more. If you’re still unsure, an HVAC professional can help you out.

10. Poor Maintenance

This is one of the biggest causes of AC units malfunctioning and is easy to avoid by cleaning regularly and getting an air conditioning check from a pro at least 2 times a year: once in the spring and once at the beginning of the autumn season.

Tips for Proper Air Conditioner Maintenance

Now, as we just mentioned, not maintaining your AC unit is one of the most avoidable yet most common causes of malfunctions. Let’s look at how you should be taking care of your AC to keep it in tip-top shape!

1. Turn off power

As we’ll be dealing with some serious voltage and moving parts, it’s crucial that before you do anything, you completely turn off power to the unit. You should find an exterior shut-off box nearby.

Also, head over to the breaker box and turn off the power as well. You can never be too certain when it comes to AC units, and you definitely don’t want to accidentally get your hand caught in moving parts.

2. Clean leaves and other debris from the interior

Even if you can’t see it, there’s a good chance that some debris has made its way inside your AC unit. Take the fan cage off the exterior condenser with a screwdriver or wrench. Now you have full access and can remove the debris manually or with a vacuum.

3. Clean the fins

Take off the exterior covers and grab a brush attachment from a vacuum to get rid of all exterior dust and grime. If you can, take a garden hose and gently spray some water through the fins towards the exterior. It’s important the hose isn’t too high in pressure as this can potentially damage the fins.

4. Straighten bent fins

If you notice the fins are bent, grab a butter knife or fin-straightening tool. Again, you must be delicate with them as they’re easy to damage.

5. Clean area around the unit

Once the fan cage is back on, move any leaves, branches, plants, bushes, etc., away from the condenser at least a couple of feet. If you get cold winters, make sure to cover the top of the air conditioner with a solid piece of wood, plastic, etc., to prevent anything from coming inside.

6. Level the unit

If your condenser unit isn’t completely level, it can start malfunctioning. Grab yourself a level and make sure that it is. However, if yours is a heat pump system, you may find that it’s slightly moving away from the foundation of your home, which is normal.

7. Clean the evaporator coil

These can be a hassle to clean, but it’ll save you a lot of hassle and money in the long run. Once inside the evaporator coil door, you may see you have to take off some foil duct tape or remove a couple of screws.

Once this is done, grab a soft brush to get rid of any grime and dirt, then spray the coil with a no-rinse coil cleaner. Once it’s all dripped away, clean out the drain pan with soap and hot water (maybe even a bit of bleach). Then, pour a cup of half-bleach, half-water down the drain.

8. Clean a clogged evaporator drain

It’s possible that some mold or algae has formed inside the drain and caused it to clog up. This is due to the warm, humid environment inside the evaporator coil. Locate the drain line where it comes out of the coil.

It’s usually a pretty short chunk of PVC pipe. Now, find where it ends and drains out. Grab a vacuum to clean the drain out.

9. Change the blower filter

These should be changed for new ones at least 2 times a year (again, spring and fall). Make sure the new filter has the same airflow rating as the old one.

10. Turn the power back on

Just like with a lot of our modern-day technology, doing a simple reboot is an easy way to fix certain issues. Not only that but make sure the ducts are cleaned out as well.

People Also Ask (FAQ)

Why won’t my AC cool below 75 degrees?

This is almost always going to be caused by one of the aforementioned reasons. Check your filters and make sure they’re clean, make sure nothing is clogged, and that there aren’t any leaks.

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

Yes! Please turn it off ASAP and call up your local HVAC professional.

Why is my window air conditioner running but not cooling the house?

If your window AC is not cooling the house, it could be low on refrigerant/leaking, the air filters could be dirty, the coil could be frozen, and it could even be too small for your home!

What does it mean when your AC blows out hot air?

First, check that your AC unit isn’t set to “heat.” If it is, then that’s an easy fix: simply set it back on to “cool”! If that isn’t the case, then you could have an issue with the compressor or have a refrigerant leak.

How do you know if your AC is low on Freon?

If the air conditioner is running but doesn’t cool, if the unit is blowing out warm air, if electricity bills are abnormally high, if you see ice or frost forming on the unit, or if you hear any weird hissing or bubbling noises coming from the refrigerant line, it’s likely that it’s low on Freon.

When is the average life of an air conditioner compressor?

With proper maintenance, you can expect your air conditioner compressor to last anywhere from around 12 to 15 years, which is impressive!

How many hours should AC run per day?

There really isn’t a limit when it comes to how long your AC can run per day. Perhaps just a few minutes or half an hour is enough to cool down your house. Maybe on particularly hot days, you have it running all day! It’s all down to your own personal preference.

Conclusion

Now that you are practically an AC pro yourself, do you know the steps you need to take to fix your AC cooling issue? Remember, if you don’t feel confident or aren’t sure what the problem is, call up an HVAC pro to get it taken care of.

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.

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