The Most Common AC Problems and How to Fix Them: An Expert's Perspective

As an HVAC expert with years of experience, I have encountered numerous air conditioning problems. From frozen coils to faulty thermostats, there are a variety of issues that can arise with your AC unit. In this article, I will discuss the most common problems with AC units and provide tips on how to fix them.

Old, Clogged Air Filters

One of the most common culprits for AC problems is an old or clogged air filter. Over time, dust and debris can build up in the filter, restricting airflow and causing the unit to work harder than it needs to.

This can lead to frozen coils and other issues. It's important to regularly check and replace your air filter to ensure proper functioning of your AC unit.

Low Coolant Levels

If your air filter is not the problem, then you may be low on coolant. You can test this by feeling the larger of the two copper lines that go to the unit's condenser. If it feels warm, then you may be low on coolant.

This can be caused by a leak or an incorrect charge during installation. It's important to have a trained technician check and fix any coolant issues.

Closed Rooms and Interrupted Airflow

Another common issue with central air conditioning is when rooms are closed off, interrupting the airflow through the house. This can cause uneven cooling and put strain on your AC unit. To avoid this problem, make sure to close all windows and outside doors when using your AC and try to isolate the room or group of connected rooms as much as possible from the rest of the house.

Faulty Installation and Maintenance

Many AC problems can be traced back to faulty installation or inadequate maintenance.

Incorrect installation can lead to duct leaks and low airflow, while inadequate maintenance can result in dirty coils, clogged drain lines, and refrigerant leaks. It's important to hire a qualified technician to install and maintain your AC unit to avoid these issues.

Thermostat Malfunction

A faulty thermostat is another common problem with household air conditioners. If your AC is running on short cycles and the space feels warmer than usual, it may be due to a malfunctioning thermostat. In this case, it's best to have a professional technician replace the thermostat.

Frozen Coils

If your AC unit has frozen coils, the first step is to turn it off and allow the coils to defrost.

This can take up to 24 hours, but you can speed up the process by changing the setting to “fan only”. This will cause hot air to enter the coils without going through a cooling cycle. It's also important to regularly check and replace your air filter to prevent frozen coils.

Refrigerant Leaks

Refrigerant leaks are not only harmful to the environment, but they can also cause problems with your AC unit. If you suspect a refrigerant leak, it's important to have a trained technician repair the leak and charge the system with the correct amount of coolant.

It's also worth noting that newer AC units use more environmentally friendly refrigerants such as Puron or R-410A.

Clogged Drain Line

Your AC unit uses a condensate drain line to remove water from the air. If this drain becomes clogged with mold or debris, it can cause water to build up and leak from your unit. To prevent this issue, it's important to regularly maintain your AC unit and have a professional clean the drain line if necessary.


In conclusion, there are a variety of common problems that can occur with AC units. By regularly maintaining your unit and hiring a qualified technician for installation and repairs, you can prevent many of these issues.

Remember to regularly check and replace your air filter, and if you notice any problems with your AC unit, don't hesitate to call a professional for assistance.