Air Conditioning Troubleshooting: Common AC Problems & Solutions

After spending hundreds of dollars purchasing an HVAC system, it is frustrating having to spend hundreds more trying to fix it.

Unfortunately, like all other appliances, air conditioners haves advantages and disadvantages; and sometimes they have a nasty habit of letting us down when we need them the most. But before you call an AC repairer, learning how to troubleshoot common problems can save you a lot of money.

In this post, we have provided in-depth detail of air conditioning troubleshooting and common problems associated with ACs. 

Air Conditioning Troubleshooting  (Common AC Problems and Solutions)

1. AC Not Cooling as Expected

There is nothing more frustrating than an air conditioner that doesn’t cool, but sadly, this is a familiar problem.

There are several reasons why your AC would not be cooling as it should. Here are the things you need to look for in order:

  1. The first place to check is the thermostat. Make sure that it is on and it has been set right. You may need to install new batteries if it is not responsive.
  2. Check the filters. Dirty filters will reduce the cooling power. You can either clean them or replace them if they are too old.
  3. The next step would be to clean the coil in the outside condensing unit. If that doesn’t work, then clean the inside coil.
  4. Check if the refrigerant is leaking.

While the first two steps are things you can do yourself after watching a YouTube video or two, you might choose to call an HVAC repairer to clean the coils and check for any leaks.

If you’re wondering what to look for when hiring an hvac technician our guide here has detailed the steps for you. 

But before you call just anybody, find out if your installer has a service plan that covers coil cleaning, filter cleaning, and any other routine maintenance.

If the cause of your AC not cooling is that you are running low on refrigerant, then a repairer will check for leaks. A common misconception is that refrigerants or freons are like fuel, and they eventually run out.

On the contrary, the refrigerant should last the entire lifespan of your air conditioner unless there is a leak. While you may be able to identify a leak, you need to call a professional to fix it and top up your freons to the right level.

2. The Air Handler is Leaking Water

While this may not affect the operation of your air conditioner, it can damage your walls, floorings, and any furniture in its path.

So, no matter how small the leak is, you should attend to it immediately. 

Here are some of the common causes of this:

  • Clogged condensate drain line – the drain can be blocked by dust, mold, dirt, or sludge. You can unclog it using a wet/dry vacuum or call a professional to use a more precise tool.
  • Clogged drain pan hole – the hole from the drain pan leading to the drain line can also be blocked by dirt, sludge, and algae. So, instead of the water entering the line, it is simply spilling over. You can flush the drain to clear this out.
  • A broken or rusted drain pan – this will cause the water to drip out of the AC unit before it gets to the drain line. This is more common for systems over a decade old. The solution is to replace the pan.
  • Broken condensate pump – indoor units installed in a basement have a condensate pump that forces the water outside. When this breaks, the water drips out, and the pump will need to be replaced.
  • Dirty air filter – it cannot be overstated how important it is to clean air filters regularly. This is just one of many potential side effects of leaving them dirty.

Another potential cause of indoor leakage is a frozen coil. However, it is an important topic that deserves to be discussed individually.

3. AC Not Working

Unlike the first problem on our list, this one has to do with the AC not cooling at all. If your air conditioner turns on and off right away, then you should first inspect the electrical panel.

  • Ensure the AC circuit in the electrical panel is on. There are many reasons why the circuit breaker might trip, including a power surge, fan motor malfunction, faulty compressor, and so many others. Flip it back on and wait for thirty minutes before putting on the air conditioner.
  • Check the external circuit near the condensing unit. This circuit can also trip for several reasons. Put it back on and follow the same process as above. If the problem is the circuit panel and it trips again, you need to call a specialist to fix it.
  • If the problem is not the panel, check to see if the circuit control boards are flashing LED codes. The codes will tell you what is wrong, and you may then get external help if you can’t do it yourself.

If the problem isn’t the circuit board, then you might need to flush the drain line. If that fails, call a maintenance specialist, as other possible causes, such as a broken condensation pump, should be handled professionally. Read more to know if it’s safe to run an AC all day long.

4. The AC is Over-cooling Your Home

This is probably the best thing that could go wrong in your home. Of course, the downside is you’ll be left with an astronomical electric bill.

The most common reason for an air conditioner cooling beyond the thermostat setting is that the thermostat is close to a heat source.

This could be a lamp on the wall or an electrical object emitting heat, causing the thermostat to misread the room temperature.

Another reason could be a faulty thermostat. When the thermostat is covered in dust, it cannot read the room temperature correctly, leading to over-cooling.

The solution, in this case, would be to clean the thermostat. Depending on the design, you might be able to do this by using a small brush and compressed air to clean between the levers and contact points gently.

5. Frozen Evaporator Coil

If your AC isn’t working and you notice ice on the condensing unit outside, it means the evaporator coil has frozen.

The evaporator coil is what holds the refrigerant in an AC. It runs on a loop inside and outside. The refrigerant absorbs warm air from inside the house and expels it outside. If there is no warm air reaching the evaporator, then it will freeze.

Several things can stop the flow of air to the coil, including a dirty coil, blocked air ducts, leaking refrigerant, and a few others.

To solve this problem, you need to switch off your AC and run it on fan-only mode. As the fan runs, it will thaw the unit, which could take anywhere from one day to two.

As the evaporator coil thaws, the water will most likely drip directly on the ground by the furnace instead of flowing outside. Make sure you move any sensitive furniture away, roll back your carpet, etc.

Before you put the AC back on, clean the coil and the filters.

If the reason for the frozen evaporator coil is low freon, it is best to call a technician. You need a license to buy freon, specialist tools, and the expertise to recharge your unit correctly.

6. AC Outdoor Fan not Working

One reason for an AC to stop cooling is that the fan outside is no longer spinning. The fan on the outdoor unit is meant to help expel the heat gotten from the indoor unit.

If the fan stops running, the system can overheat and cause all sorts of problems. There are different reasons why this could happen, depending on which one of these two things is happening:

The compressor is running, but the fan isn’t spinning, or there is no sound at all from the external unit, and the fan also isn’t spinning.

If the compressor is working, then there is a problem with the fan motor, the start capacitor, or both.

When the start capacitor is faulty, it will not provide the spark needed to make the fan start spinning when the unit comes on. You can “jump-start” it by using a stick to propel the fan and see if that works.

However, this is only a temporary measure, and you should call a repairer to check the unit. If the jump start doesn’t work, switch off your HVAC, so you don’t risk overheating the compressor while you wait for the expert.

If the compressor is not coming on, it could mean the circuit breaker has tripped. If so, switch off your unit with the thermostat, then flip it back on.

If there is no problem with the circuit breaker, you may have a faulty compressor, and you need a technician to check it out.

7. HVAC System Making Unusual Noise

Air conditioners are loud, especially when they are set on low temperatures and high fan speeds. That is not unusual.

It is also normal for the condensing unit to make a bit of noise when you first put it on, then the sound fades into the background.

However, other sounds can make you panic. Here are some of the most frequent ones: 

  1. Popping or cracking: sudden loud pops can make you feel like the indoor unit is about to fall. However, this is a typical sound, and it usually happens as ducts expand and contract. But if you have had your system for a while and this is the first time you are hearing it, you should call a technician.
  2. Low humming, but the fan is not on: a bad fan motor or a faulty compressor can give off a low, constant humming sound. You should get a technician to find out which one is faulty and needs to be changed.
  3. Banging: banging is never a good sign, but it may also not be so bad. Banging usually means there is a loose component swirling around. In rare cases, it means a faulty compressor. In either case, switch off your unit and wait until a professional inspect it.
  4. Vibration hum: if you can hear a hum caused by vibrations in your condensing unit, it usually means something inside is loose, not broken. This is a much easier fix than a banging sound. Open up the unit and tighten any fasteners to see if that will stop the noise.

You may also need to place foam rubber between any parts that might be in contact. If that doesn’t stop the noise, you can call a professional.

  1. Clicking sound: it is normal for some air conditioners to click when they start, but if this persists, then it usually means an electrical fault. Electrical faults should be handled by professionals, as they can turn hazardous very quickly.
  2. Buzzing noise in the condensing unit: similar to the sound above, condensing units buzz at the start of operation. If it continues and the AC does not come on, the issue might be a bad capacitor, bad start relay, or some other electrical fault.
  3. Light hissing: just like with animals, your air conditioner hissing means danger is around the corner. Light hissing in the walls means there is air leakage in the ducts. This won’t damage your unit immediately, but it will drain your electricity, and it will get worse over time if not repaired.
  4. Screaming or high-pitched hissing: loud hissing might indicate refrigerant pressure in the system. You should switch off your system immediately to avoid the compressor exploding or some other catastrophic damage to your unit.

Don’t switch it back on until a technician has had a chance to inspect the unit thoroughly.

  1. Whistling: leaking refrigerant can cause a whistling sound, which may be the result of debris clogging up the thermostatic expansion valve (TVX). TVX controls the amount of refrigerant flowing into the evaporator. In either case, issues with refrigerant should not be taken lightly, and you need an expert on your premises immediately.

 8. AC Smells Like Chemicals

The human brain has been taught to associate chemical smells with danger, and for a good reason. However, if your AC is smelling like chemicals, there might be a simple reason for it, so don’t panic.

There are three common causes of your AC smelling of chemicals:

  1. The AC is diffusing an external smell – if there are chemicals near your unit, the AC could simply be spreading that smell. Things like paint, solvent, cleaning supplies, or fertilizer carry a strong smell which your AC might be circulating, so all you have to do is move them away.
  2. Refrigerant leak – if the smell is similar to the coolant you use in your car, then it could mean a refrigerant leak. While you can try to identify where the leak is, it is best to call a technician.
  3. Mold – if you live in a very humid place, then it is possible to get mold on your drip pan or the AC coil. You can DIY clean the AC coil or drip pan yourself or call a repairer to help.

Benefits of learning DIY

Being able to troubleshoot common problems can save you a lot of money over time. Depending on where you live, each service call can cost between $75 – $200, even if all the repairer does is flip the circuit breaker.

The most important things to know how to protect are your coils. Coil replacements cost between $2,000 – $3,000/.

Therefore, it is helpful to learn how to clean them and protect them from any damage by also learning to use your system the right way.

If you need to call a professional, ensure you go for the best, not the cheapest, which can cost you more money in the long run.


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Ronald Watford, the owner of Quality Home Air Care, is a qualified HVACR technician and manages the team of expert writers on this site. He believes that educating homeowners about HVAC systems is one of the most impactful aspects of his job.