14 Most Common Home AC Problems (And How to Fix Them)

By David Heacock

We understand you want to take care of your AC system the best you can. That means doing what you can to prevent the most common air conditioner problems from happening in the first place. But no matter how careful you are, home AC problems can still occur. When they do, diagnosing home AC problems and getting them corrected as soon as possible is extremely important, so it doesn't cause a chain reaction of more costly issues.

For your comfort and safety, as well as the safety of your air conditioning system, we've created this summary outlining the most common home AC problems and how to fix home AC problems before calling a professional.

Diagnosing and Fixing Common Home AC Problems:

Air conditioner problems can happen to any system, even new ones, if they aren't installed or maintained properly. So keep an eye out for these warning signs if you're diagnosing home AC problems.

Find your Common AC Problem by clicking below:

• #1 – AIR CONDITIONERS ARE CONSTANTLY RUNNING
• #2 - AC UNIT DOESN'T TURN ON
• #3 - AIR FLOWS BUT DOESN'T SEEM "CONDITIONED"
• #4 - AC IS BLOWING HOT AIR
• #5 - AC UNIT IS STOPPING AND STARTING CONSTANTLY
• #6 - AC UNIT IS TRIPPING CIRCUIT BREAKER
• #7 - CENTRAL AIR SMELLS OFF OR BAD
• #8 - AC UNIT IS CAUSING A WATER LEAK FROM AIR VENTS
• #9 - WATER IS LEAKING FROM AC CONDENSER OUTLET ON EXTERIOR OF HOUSE
• #10 - AIR BOX FAN ISN'T TURNING ON
• #11 - DUST GATHERS QUICKLY ON SURFACE
• #12 - AIR BLOWS ESPECIALLY COLD IN ONE ROOM OF THE HOUSE
• #13 - BLOWN AIR SMELLS LIKE ITS BURNING
• #14 - HUGE INCREASE IN MONTHLY ENERGY BILL

Home AC Problem #1 – Air Conditioners are Constantly Running

• The Issue: The AC is constantly running and can't reach the temperature you've set. In that case, it leads to an uncomfortable temperature in your home throughout the day (especially during the summer months) and causes a spike in your monthly energy bill.
• Possible Causes: A lot of issues can cause your AC unit to run constantly. Dirty air filters can make your system work harder to reach the ideal temperature, or you could have a coolant leak that diminishes your unit's ability to cool the air.
• How to Check: Set your thermostat to 1 – 2 degrees below the current temp and see how long it takes for your AC unit to cycle off. In most cases, it should shut off in a couple of hours. If it doesn't shut off, your AC unit is constantly running.
• How to Fix the Home AC Problem: In some cases, it may be as simple as replacing your air filter, spraying debris out of your exterior air box, and setting a proper temperature schedule during the day. However, if none of those seem to improve the issue, you may want to contact an HVAC professional to run a diagnostic test for leaks in your system and see if parts need replacing.

Home AC Problem #2 - AC Unit Doesn't Turn On

• The Issue: AC unit won't turn on after changing the thermostat setting or turning the thermostat on.
• Possible Causes: There could be a circuit breaker that's tripping. Another issue could be that the thermostat is no longer communicating with the AC system.
• How to Check: Reset the circuit breaker. If the AC still won't turn on, the thermostat is likely to blame.
• How to Fix This Home AC Problem: The problem should be fixed if the circuit breaker was the issue. However, you may want a licensed electrician to look at the circuit breaker and wiring system to make sure it's not overloaded by the AC turning on. If the thermostat seems to be the problem, you can try installing a new unit or have an HVAC technician look at it.

Home AC Problem #3 - Air Flows But Doesn't Seem "Conditioned"

• The Issue: When the AC unit is just cycling air through the vents, but it isn't hot or cold, It just doesn't seem to be "conditioned."
• Possible Causes: There could be several reasons this is occurring. It ranges from a dirty condenser coil to needing a more appropriately sized HVAC system.
• How to Check: Track when the problem occurs; if it's in the summer in the middle of the day, the AC system may have difficulties compensating for high temperatures outside. On the other hand, if the issue is all day long, it could be a mechanical or maintenance problem.
• How to Fix This Home AC Problem: The system capacity may be inadequate if the problem occurs during the hottest time of day. You may need to replace the existing system with a variable speed HVAC unit to resolve this issue. But if you don't want to replace your system completely, try weatherizing the house and practicing energy efficiency to ease the amount of work the HVAC has to do. If the issue occurs all day, the HVAC system needs to be inspected to determine the cause and best fix.

Home AC Problem #4 - AC Is Blowing Hot Air

• The Issue: The AC blows air just fine, but it's hot air.
• Possible Causes: A refrigerant leak or low refrigerant is the first problem that comes to mind. However, there could be a variety of reasons this is happening. A common cause is dirty air filters that lead to a dirty evaporator coil and clogged condenser coils in the outdoor unit.
• How to Check: First, check the thermostat to make sure it was accidentally set to heat. If that isn't the problem, inspect the air filter. A dirty air filter means you also need to examine the evaporator coil. If the air filter looks clean check out the outdoor unit to see if it's getting adequate airflow.
• How to Fix This Home AC Problem: Hopefully, all you have to do is give the system a cleaning. Replacing the air filter, cleaning a dirty evaporator coil, and clearing out the debris inside and vegetation around the outdoor unit could correct the issue. However, if none of that works, it may be time to call a technician to top off the refrigerant.

Home AC Problem #5 - AC Unit is Stopping and Starting Constantly

• The Issue: The system is short cycling, meaning it is continuously turning on and off for less than 15 minutes at a time.
• Possible Causes: There are a lot of potential causes because short cycling is a symptom of something else being off in the system. It can be as simple as a dirty air filter or a small refrigerant leak. Also, the issue could be as complex as the AC system being too powerful for the electrical wiring. Whatever is happening, it's causing the AC system to get stuck in the startup cycle or putting strain on the blower motor.
• How to Check: The first thing you should do is check the air filter. Next, check the thermostat to make sure it's working properly. If neither of those seem to be the issue, it's most likely a refrigerant leak.
• How to Fix This Home AC Problem: The fix is simple if the air filter or thermostat is the problem - replace them. If there's a refrigerant leak, you'll need an HVAC specialist to have the issue repaired. They can also help you determine if your HVAC system is appropriately sized for the home.

Home AC Problem #6 - AC Unit is Tripping Circuit Breaker

• The Issue: The circuit breaker is tripped when the AC turns on.
• Possible Causes: The circuit breaker tripping is a good thing because it can help prevent electrical fires. But it's an indicator that one of four things is happening: there's a short circuit, the breaker is bad, refrigerant pressure is off, or the system is drawing too many amps.
• How to Check: Again, check your air filter first. A heavily clogged air filter can make the system work harder and draw more amps. Dirty condenser coils are another thing that can add to the problem. If dirty equipment isn't the problem, it is likely a mechanical or electrical problem that needs to be inspected by a pro.
• How to Fix This Home AC Problem: Homeowners can easily replace their air filter and even clean the condenser coils. But fixes to the circuit breaker and wiring system should only be handled by a licensed electrician. And if there are refrigerant pressure issues, fixing requires the help of an HVAC technician.

Home AC Problem #7 - Central Air Smells Off or Bad

• The Issue: The air coming from the air conditioner smells bad or off somehow.
• Possible Causes: There are a few clear causes for foul-smelling AC air. Drainage issues that lead to standing water, leaking fluids causing fumes, a fan motor that's short-circuiting, dead animals in the air ducts, and mildew growth in the AC system are all common causes.
• How to Check: Diagnosing the home AC problem often comes down to the smell. The smell of rotten eggs suggests a dead animal. Gas or exhaust odors indicate a fluid leak. Finally, the all too familiar mildew smell will give it away.
• How to Fix This Home AC Problem: When smells become a problem, professional cleaning is usually the fix. You may also need to track down a fluid leak and patch the system.

Home AC Problem #8 - AC Unit is Causing a Water Leak from Air Vents

• The Issue: There is water leaking out of the air vents. Water leaks are an issue that can cause serious damage to the AC system, ceilings, walls, and floors.
• Possible Causes: If you see moisture around your vents, it could be from a combination of factors. The issue could occur because of inadequate insulation around ducts, a clogged condensate drain line, frozen evaporator coil, dirty air filter, or refrigerant leaks.
• How to Check: The key is to find out where the moisture is originating. Start by checking your air filter to see if it is wet or dirty. Next, check the ducts to gauge how well they are insulated. If the airflow is low or the air isn't cooled well, a refrigerant leak is causing the moisture since humidity isn't being removed from the air. Finally, check the evaporator coil and condensate drain line. The evaporator coil is likely the issue if the moisture occurs mostly when the AC system is turned off. If the outside condenser unit drain pan is full, the problem is happening in the drain line.
• How to Fix This Home AC Problem: Most likely, it won't hurt to improve the insulation around the ducts and replace the air filter to help remedy the problem. However, if the problem seems to originate in the evaporator coil, condensate drain line, or refrigerant, you'll need to call an AC technician to fix this air conditioner problem.

Home AC Problem #9 - Water is Leaking From AC Condenser Outlet on Exterior of House

• The Issue: If you see water leaking out of the AC condenser outlet pipe on the house's exterior, it's a more specific problem. And it's a problem that needs to be addressed ASAP since it can signal significant air conditioner problems and do damage to your home.
• Possible Causes: A small amount of condensation leaking is normal, especially during the hot summer days. However, if there's considerable leakage, it's usually due to a clogged condenser line. There could also be another simple problem like a cracked condensate pan or dirty air filter. Worst case scenario, the AC system was installed incorrectly and isn't draining properly.
• How to Check: Start by examining how much water is leaking out. If it's more than a small puddle, it's a problem. Next, look to see when water is leaking out of the outlet pipes. Water leaks during operation are normal but continuous leaking is not.
• How to Fix This Home AC Problem: The first thing you should do is replace your air filter if it's dirty. If that solves the problem, great! But if the problem persists, you need an AC professional to clear out a condensate drain line clog, replace a broken pan, or reinstall the equipment to function properly.

Home AC Problem #10 - Air Box Fan Isn't Turning On

• The Issue: The AC air box fan won't turn on even though the thermostat says it's running. You'll probably first notice that although the system appears to be on, it's not cooling off inside like normal.
• Possible Causes: When the outside unit has stopped working, the problem is usually a big one. For example, the motor in the outdoor unit may have burnt out, there are bad capacitors, or the power supply is inadequate. But there could also be a simple reason why the outdoor unit isn't working, such as a tripped circuit breaker.
• How to Check: First, go outside to verify that the exterior box fan isn't running and that the emergency shut-off switch isn't engaged. It may sound like the electrical unit is running, but you don't feel or see any movement from the fan. That will tell you definitively if your AC air box isn't working. Hopefully, you check the electrical panel and discover there's a blown fuse or tripped circuit. If not, try resetting the AC unit. If the outdoor unit isn't working, there's something wrong internally that a technician will need to check out.
• How to Fix This Home AC Problem: You can try the DIY fixes noted above while you're checking out the issue. A technician will need to test the system to track down the problem when those don't work. Bad capacitors, contactor issues, and blown motors will need to be replaced entirely. Inadequate power supplies may need to be addressed by a licensed electrician.

Home AC Problem #11 - Dust Gathers Quickly on Surface

• The Issue: You notice that a layer of dust is coating everything in your home even though you just dusted it a few days ago.
• Possible Causes: This common home AC problem is almost always the result of a dirty air filter. There could also be leaks in the ductwork that is allowing dust to circulate through the AC system.
• How to Check: Like so many other common home AC problems, the first thing to do is check the air filter. If it's dirty, you know that it is a problem or at least contributing to it. Next, where possible, check the ductwork for leaks; this is a must if the air filter is clean yet you still have dust settling in a matter of days. Dust build-up around vents indicates a leak in the ductwork allows dirt and debris into the HVAC system.
• How to Fix This Home AC Problem: This one is usually an easy fix. Once you replace your air filter, the problem should resolve since air contaminants can now be captured. However, leaky ducts may require the knowledge of a professional who's equipped to inspect the ductwork. Small leaks can be repaired with HVAC aluminum foil sealing tape alone. Larger leaks will need a professional.

Home AC Problem #12 - Air Blows Especially Cold in One Room of THE House

• The Issue: Have you noticed one room in the house is much colder than the other rooms? Blowing super cold air in just one room or portion of your home is a very common home AC problem.
• Possible Causes: This problem is usually caused by one of three things: how the vents are set up and positioned, unbalanced or leaky air ducts, and inadequate insulation in parts of the home.
• How to Check: You'll want to check the vents and registers first to make sure they are fully opened in the rooms that aren't cooling off. Next, check the dampers to ensure they aren't closed and inspect the air filter to see if it needs to be changed. Finally, if possible, take a look at the ductwork and insulation to ensure they are adequate and in good working condition.
• How to Fix This Home AC Problem: The trick to fixing this problem is balancing out the airflow to circulate evenly throughout the home. HVAC balancing or zoning is the process of thoroughly assessing how the vents are set up and how air flows in the house. HVAC zoning means that the air conditioning system is set up in zones. This is a good idea for multi-level homes and homes with ample square footage. To balance the airflow, you can adjust the dampers in the ductwork to redirect the airflow. The registers can also be opened and closed to change how air flows into each room. Depending on how the inspection goes, you may also need to fix the ductwork and add insulation in certain spots around your home.

Home AC Problem #13 - Blown Air Smells Like Its Burning

• The Issue: When the air coming out of the vents smells burnt, it's a clear sign that something is off. You may also notice warm air instead of cooler air.
• Possible Causes: Most likely, what's happening is dust and debris have built up in the AC unit, and it's causing the heater to come on instead of the air conditioner. It could also be the dust burning off. Of course, a dirty air filter can be a contributing factor. An overheating motor is another possible cause, and though it's rare, burning electrical components could be creating the smell.
• How to Check: Once again, you'll want to check the air filter to see if it needs to be changed. If the air filter looks fine, the motor or an electrical component is most likely the problem. Those issues require an inspection by an HVAC technician.
• How to Fix This Home AC Problem: A homeowner can easily change their air filter, but the other issues will need to be addressed by a professional. You may need to replace a single component, like a broken capacitor, or the whole motor may need to be replaced.

Home AC Problem #14 - Huge Increase in Monthly Energy Bill

• The Issue: You check your checking account and notice the utility bill is way higher than normal. While this isn't directly an issue with the HVAC system, it indicates it's time to start diagnosing home AC problems. Anytime your energy bill spikes but usage hasn't changed, it suggests something is seriously off, such as a major leak in the ductwork or plumbing.
• Possible Causes: A lot of different things could be going on if your energy bill spikes suddenly. The possible causes include everything from a dirty air filter to improperly installed ductwork to low refrigerant. Bottom line: something may be making the system work harder than normal.
• How to Check: You can do a general HVAC inspection yourself to check things like the air filter. The ENERGY STAR HVAC maintenance checklist is a good resource for covering the major components.
• How to Fix This Home AC Problem: The fix will depend on what's off in the HVAC system. It could be as simple as replacing the air filter or as complex as installing a new system.