When you turn your air conditioning on, you expect to feel refreshingly cool air come flowing from your vents. It is a surprise, and makes your stomach sink, when the air coming out is warm, especially on the hot and humid days of summer. Discover what makes your system produce the cool air, and why you may have warm air coming out instead of the cool air you crave.

How Your Air Conditioner Works

Before jumping into specific reasons why your air conditioner could be blowing hot air, it is helpful to know how it works. Air conditioning doesn’t actually produce cold air but rather removes heat from the air moving through it, thus making it colder.

It does this using the refrigerant in the system, making it cold enough to absorb heat inside and then making it hot outside to exhaust that heat. When the refrigerant’s pressure drops, it gets exceptionally cold. Conversely, when you compress it, it gets hot. To continue working properly, your system must be able to regulate the refrigerant’s pressure.

Likewise, it must also have enough air moving through it. If there’s an airflow restriction somewhere in the system, it could prevent enough air from circulating to effectively cool it. Now that we understand the concepts that make your system work, let’s explore the specific things that may make it blow warm air.

Your Thermostat’s Set Improperly

Let’s start at the easiest and most common issues and ones that you can easily fix. Start by checking your thermostat. It is actually easy to change settings, and then wonder why you are feeling warm air move through your system.

There is a fan setting on your thermostat, usually with two options that include “Auto” and “On.” Changing the setting to “On” keeps your circulating fan running all the time, regardless of whether the compressor is on or not. Without the compressor running, the air coming from the vents will feel warm rather than cool.

Clogged Air Filter

As your air filter removes contaminants before they can collect in your system, it gets dirty and slowly clogs. This prevents air from flowing through the system at the volume needed. The result is less air coming out of your vents, plus that air will feel warmer than you normally expect.

Plan to check and change your filter regularly to prevent your filter from clogging. Most filters need replacing anywhere from every 30 days, for flat 1- and 2-inch filters, to as much as 9-12 months for pleated 5- and 6-inch filters. Plan to check your filter monthly to catch it before it causes strain on your system. Give it an efficiency boost when you check it by gently vacuuming off the intake side.

Low Refrigerant

As previously discussed, your refrigerant plays a critical role in conditioning your air. A lack of refrigerant in your system prevents it from reaching the proper pressure, which means it will never exhaust the heat it has absorbed from within your home, creating a perpetual cycle. This leads to warmer air coming from your vents as it runs.

Additionally, low refrigerant also means you’ll likely experience freezing in the system. As refrigerant pressure drops, it gets cold. When this happens in places where it is not intended and to a greater degree than is normal, it will cause freezes. This can lead to frozen refrigerant lines, plus frozen evaporator and condensing coils.

Failing Compressor

A failing compressor will also produce warm air from your vents for much the same reasons as low refrigerant results in this problem. It will fail to raise the pressure in your condensing coil, leaving too much heat in the system. Depending on the problem with your compressor, it could also lead to a refrigerant leak, compounding the problem.

Outdoor Unit Lost Power

Your condensing unit sits outside your house and houses the compressor. If this unit loses power, it will fail to compress the refrigerant. If it is working properly, your system should prevent any part of the system from initializing if the compressor doesn’t work. However, once you check your thermostat switch and air filter, you may want to double-check your unit.

While the system inside is running, go outside and see if the fan on the condensing unit is spinning, and see if you hear the compressor humming. If not, turn the system off, and then check the circuit breaker inside.

Dirty Evaporator Coil

While your air filter will remove most of the airborne contaminants, the smallest particles will still get through. They will settle on the evaporator coil, slowly building a type of insulation. This prevents the refrigerant from absorbing the heat as the air cycles through the system.

Faulty Expansion Valve

The component that makes the refrigerant’s pressure drop at the evaporator coil is called the expansion valve. While it is not a common issue to see, failed expansion valves do happen. When they fail, they may allow too much refrigerant into the evaporator coil, preventing the pressure from dropping enough. With a higher pressure, the coil doesn’t get cold and fails to absorb heat from the air.

Blocked Condensing Unit

Even with enough refrigerant in the system and the compressor working properly, your condensing unit may fail to vent the heat. This can easily happen when there’s debris blocking air from circulating through the outside unit. You should keep the area around your unit clear to prevent this restriction. Keep at least 12 inches clear, but 2 to 3 feet is more ideal. This includes keeping brush, bushes, and trees trimmed back. It also means keeping weeds under control so that they don’t grow up around the outside of the unit.

Duct Leaks

Even with your air conditioner working well, leaks in your ducts may also allow warm air to come from your vents. If you have substantial leaks in your system, it can cause several potential problems. First, it can allow that conditioned air to leak out, reducing what is actually coming from your vents. It could also allow warmer air in as it heads to your vents, warming what is coming out.

Keeping Your AC Blowing Cold Air

Attending to a few simple tasks will help ensure you keep your AC blowing cold air for its full service life. As mentioned previously, keep a close eye on your air filter and change it regularly.

Next, plan to get routine maintenance for your system every year. A technician will perform a deep clean, including your evaporator coil. They will also tighten mounting hardware and electrical connections to prevent system strain. Finally, they’ll test your system, including your compressor and refrigerant level, to ensure that it can maintain the proper pressure.

For over 30 years, people around Gainesville have trusted Gee Heating & Air to keep their homes comfortable and safe. Our expert technicians provide heating and air conditioning installation, repair, and maintenance. You can also turn to us for indoor air quality solutions. Call to schedule your air conditioning maintenance or repair with one of our friendly technicians today.

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