20 Common AC Problems You Should Know About & How To Fix Them

Published: 06 Jun 2025

Did you know nearly 85% of air conditioner failures stem from issues that could have been prevented with early detection or simple maintenance? From refrigerant leaks to faulty sensors, most AC breakdowns don’t happen overnight — they’re the result of minor problems that go ignored.

This guide breaks down the most common air conditioning problems, what causes them, and how you can fix or prevent them before they cost you big.

Table of Content

Signs Your AC Is in Trouble
Common AC Problems and Easy Fixes
Preventive Maintenance Checklist for Homeowners
Conclusion

Signs Your AC Is in Trouble

Sometimes, your AC won’t stop working all at once. Instead, it shows minor warning signs. If you catch these early, you can avoid bigger problems later. Here are three signs to look out for:

1. Temperature Doesn’t Stay the Same

Is one room cool while another stays warm? Or does the air feel weaker than before? This means your AC may not be working right. It could be a filter, a duct problem, or something else. Either way, it’s a sign to get it checked.

2. Energy Bills Are Going Up

If your power bill keeps climbing, your AC might be using more energy than it should. This occurs when the system overexerts itself. Something inside may be dirty or broken. A tune-up can help bring those bills back down.

3. Water Stains or Strange Sounds

Do you see water around your AC? That’s not normal. It could mean a drain is blocked. Also, listen for sounds like buzzing, banging, or rattling. These noises are signs that something is loose or not working right.

Common AC Problems and Easy Fixes

Your air conditioner might stop working for many reasons. Some problems come from inside the machine. Others are caused by air ducts, power supply issues, or even animals. This guide covers all the main types of AC problems in one place. Each section explains what’s wrong, why it happens, and what you can do about it.

Air Conditioner Mechanical and Cooling Issues

Your AC might stop working the way it should. These are some of the most common issues that people encounter. Let’s look at each one, what causes it, and how you can fix it.

1- AC Not Turning On

Your AC doesn’t start, even when you lower the temperature on the thermostat. Nothing happens. No sound. No cool air.

Cause: This can happen if the circuit breaker is off, the thermostat isn’t working, or the wires inside are loose or broken.

Solution: First, check your thermostat to ensure it has working batteries. Then, look at your circuit breaker and switch it off and on. If that doesn’t work, call a technician to check the wires and other parts.

2- AC Running Constantly

Your AC never takes a break. It keeps blowing air all day, even after your home feels cool.

Cause: Your thermostat might be broken. Or, the AC might be too small for your home. Dirty filters can also cause this because they block the airflow.

Solution: Start by cleaning or replacing the air filter. If that doesn’t help, have a professional inspect the thermostat and the size of your AC unit.

3- No Cool Air Flowing

The AC is on, but you feel no cool air—or barely any at all.

Cause: This could be due to a clogged filter, a frozen coil, or low refrigerant levels. It can also be a broken fan that isn’t pushing air through.

Solution: Replace the air filter. If the problem continues, a technician should check for frozen parts or low refrigerant (the gas that cools the air).

4- AC Blowing Hot Air

You turn on the AC, but instead of cool air, warm air comes out.

Cause: This can occur if the refrigerant level is low, the compressor is malfunctioning, or the outdoor unit is dirty and unable to cool the air effectively.

Solution: Clean around the outdoor unit. Make sure nothing is blocking it. If that doesn’t resolve the issue, call a technician to inspect the gas level and the compressor.

5- Unit Short Cycling

Your AC turns on and off over and over again in short bursts. It never runs for very long.

Cause: This could mean the system is too big for your house. It could also be a dirty filter or a thermostat that’s not reading the temperature correctly.

Solution: Change the filter first. If short cycling continues, consider hiring a professional to inspect the thermostat or determine if your AC is the correct size.

Air Conditioner Airflow and Ductwork Problems

If your home isn’t cooling the way it should, the problem might not be inside your AC. It could be the air pathways — the vents and ducts — that carry cool air to each room. Here are some common ductwork and airflow issues that can affect the performance of your air conditioner.

1- Leaking Ducts

Ducts carry cool air from your AC to every room. If they have holes or cracks, some of that cool air escapes before it gets where it’s needed.

Cause: Leaks can occur when ducts become old or shift out of position. Rodents or poor installation can also cause tears or gaps.

Solution: A professional can check your ducts for holes and seal them using special tape or paste. Sealing leaks can improve your AC’s performance and reduce your energy bill.

2- Uneven Cooling

Some rooms feel cold, while others stay warm. That’s uneven cooling, and it means the air isn’t spreading evenly through your home.

Cause: This can happen if ducts are blocked, vents are closed, or the system isn’t balanced. It may also be a sign of leaking ducts or weak airflow.

Solution: Make sure all vents are open and not blocked by furniture. Clean your air filters and check for leaks. A pro can also adjust the system so that the air is spread out more evenly.

3- Blocked Vents & Registers

If air can’t come out of the vents, it won’t cool the room. Blocked vents stop your AC from working right.

Cause: Furniture, rugs, or curtains might be blocking the vents. Sometimes, dirt builds up inside the vents, too.

Solution: Check every room to ensure nothing is covering the vents. Clean the vents if they look dusty. Keep space around them clear so the air can move freely.

4- Improper Duct Sizing

If your ducts are too small or too big, your AC can’t push air properly. That means poor airflow and insufficient cooling.

Cause: This occurs when the ducts are incorrectly sized during installation. Small ducts cause pressure. Big ones make the air move too slowly.

Solution: This problem needs a professional fix. An HVAC expert can measure your home and suggest the proper duct size. Correct duct sizing helps your AC run more efficiently and cool your space faster.

Air Conditioner Electrical & Sensor Failures

Your AC relies on power and sensors to function correctly. If something breaks in the electrical system or a sensor stops working, your AC may stop or act strangely. Let’s look at the common problems in this area.

1- Tripped Breaker or Fuse

If your AC suddenly shuts off and won’t turn back on, it might be a tripped breaker or blown fuse.

Cause: This can happen when your AC pulls too much power. Dirty filters, blocked airflow, or faulty wiring can cause the system to work too hard, resulting in the breaker tripping.

Solution: First, check your breaker box. Flip the switch off, then on again. If the breaker keeps tripping, don’t force it. Call a technician to check what’s causing the power overload.

2- Thermostat Sensor Issues

The sensor tells your AC when to turn on or off based on the room’s temperature. If it’s not working right, your AC might cool too much or not at all.

Cause: The sensor can shift out of place or stop working over time. If it touches the coil or is too far from it, it won’t read the temperature right.

Solution: Adjust the sensor gently so it sits near the coil without touching it. If it’s still not working, a technician can replace it with a new one.

3- Electric Control Failures

Your AC uses electrical parts to control fans, motors, and the compressor. If these parts break, your system might not start, or it could stop in the middle of a cycle.

Cause: Turning your AC on and off too often can wear out the controls. Corrosion or loose wires can also prevent the system from functioning correctly.

Solution: This isn’t something to fix on your own. An HVAC technician can test the connections and replace any damaged parts safely and efficiently.

4- Faulty Wiring or Capacitor

The wiring sends power through the system. The capacitor gives the motor a boost to start. If either one fails, your AC might not turn on or may shut off too soon.

Cause: Wires can wear out, loosen, or break. Capacitors can burn out from too much heat or sudden power surges.

Solution: Don’t try to fix wiring or capacitors by yourself — it can be dangerous. A trained expert should inspect and replace these parts to ensure your system remains safe and operates efficiently.

Air Conditioner Freezing & Leaking Issues

Your AC is supposed to cool your home, not freeze up or leak. If you see ice or water around your unit, it’s a clear sign that something’s wrong. Let’s look at the common freezing and leaking problems.

1- Frozen Evaporator Coil

The evaporator coil is the part that cools the air. If it freezes, your AC won’t work properly and may stop blowing cold air.

Cause: This can happen when there isn’t enough airflow. Dirty air filters, blocked vents, or low refrigerant can all cause the coil to freeze.

Solution: First, turn off your AC and let the ice melt. Then check and replace the air filter. If the coil continues to freeze, call a professional to check for low refrigerant or other potential damage.

2- Freezing Outdoor Unit

Sometimes, the part of your AC outside the house can freeze up, too. You might see ice on the pipes or the fan unit.

Cause: Low refrigerant levels, dirty coils, or inadequate airflow can cause the outdoor unit to freeze. Running the AC when it’s too cold outside can also cause this.

Solution: Turn off the system and let it thaw. Check that the filter and outdoor unit are clean. If the problem happens again, a technician should check the refrigerant and system settings.

3- Water Leaking Outside

It’s normal to see some water near your AC on hot days. But if there’s a puddle or constant drip, it means something’s wrong.

Cause: This can occur if the drain line is clogged or the drain pan is damaged. It can also happen when the system freezes, then melts.

Solution: Clear the drain line if it’s clogged. You can use a wet/dry vacuum or pour some vinegar down it. If the leak persists, call a professional to inspect the drain pan or deeper blockages.

4- Refrigerant Leaks

Refrigerant is the gas that cools the air. If it leaks, your AC won’t cool well, and it can damage other parts.

Cause: Leaks happen when coils crack or wear out. It can be hard to spot, but you might see colored stains or hear a hissing sound.

Solution: Don’t try to refill refrigerant yourself. A certified HVAC technician must locate the leak, seal it, and replenish the system with the correct amount of refrigerant.

Noise & Smell Red Flags

Strange sounds or bad smells from your AC are never a good sign. These warnings mean something inside the system isn’t right. If you notice any of these, act promptly to prevent the problem from worsening.

1- Buzzing, Grinding, or Rattling

Your AC should run quietly. If it starts making loud or weird sounds, that usually means something is loose, broken, or worn out.

Cause: Buzzing could mean an electrical problem. Grinding often comes from a motor issue. A loose part, such as a fan blade or screw may cause rattling.

Solution: Turn off the AC to stop more damage. Don’t try to fix moving parts yourself. Call a technician who can check what’s causing the noise and fix it safely.

2- Musty or Burning Odors

Your AC should never smell bad. A musty smell could mean mold. A burning smell may indicate that something is overheating or melting.

Cause: Musty smells come from water buildup in the drain or duct. Faulty wiring, a malfunctioning motor, or an overheated component may cause burning smells.

Solution: Turn off your AC right away if it smells like something is burning. Replace the air filter and check for leaks. If the smell persists, a professional should inspect it to identify and rectify the source.

3- Animal Intrusion in Vents

If your home smells bad or you hear scratching sounds, an animal may have gotten into your AC vents.

Cause: Rodents, birds, or small animals sometimes crawl into ductwork, especially in older homes or systems with open vents. This can block airflow and spread unpleasant odors throughout the house.

Solution: Call a pest control expert to remove the animal safely. After that, have an HVAC technician clean the ducts and seal any openings to stop it from happening again.

Preventive Maintenance Checklist for Homeowners

Taking care of your AC doesn’t have to be hard. Regular maintenance can prevent major issues from arising. Use this easy checklist to keep your system running smoothly throughout the year.

Monthly Tasks

Check and change the air filter: A dirty filter blocks airflow, causing your AC to work harder. Check it every month. Replace it if it looks dusty or gray.
Look at your vents: Make sure nothing is blocking the vents—no furniture, rugs, or curtains.
Listen for odd noises: If you hear buzzing, rattling, or squealing, turn off the system and check it out.

Quarterly Tasks

Clean the outdoor unit: Remove leaves, dirt, and grass from around the outside of your AC. Keep at least 2 feet of clear space around it.
Check the drain line: Pour a cup of white vinegar or warm water down the drain line to clear out mold and dirt.
Test the thermostat: Adjust the temperature up or down and ensure the AC turns on and off as expected. Change the batteries if needed.

Seasonal Tasks (Spring & Fall)

Schedule a professional tune-up: A technician can check refrigerant levels, clean the coils, and inspect all parts before the summer season begins.
Clean your ducts (if needed): If you notice dust blowing from vents or smell an unusual odor, consider having your air ducts professionally cleaned.
Check insulation and weatherstripping: Ensure doors and windows are sealed to prevent cool air from escaping.

Keeping up with these simple tasks can save you money, prevent breakdowns, and help your AC last longer.

Conclusion

Every home and every AC unit is different. What matters is noticing when something feels off and taking steps to fix it early. I encourage you to explore the problems we’ve covered and see which one sounds most like what you’re dealing with. The sooner you understand the issue, the easier it will be to get your cool air back, without stress.

Why is my AC running but not cooling the room?

This could mean your filter is dirty or your refrigerant is low. It might also be a problem with the thermostat. A quick check or a pro inspection can fix it fast.

How often should I change my AC filter?

Check your filter once a month. If it looks dirty, replace it. Most homes need a new one every 1–3 months.

What does it mean if my AC keeps turning on and off?

That’s called short cycling. It can be caused by a dirty filter, a bad thermostat, or a unit that is the wrong size. A technician can help you find the cause.

Is it normal for water to leak from my AC?

A little water outside on a hot day is okay. But if you see puddles or water inside, something’s wrong. It could be a clogged drain line.

Why does my AC smell bad when I turn it on?

Musty smells might mean mold. A burning smell could mean an electrical problem. Always turn off the unit and get it checked.