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Air Conditioner Not Blowing Cold Air But Running

a home's ac vent

If you find your air conditioner not blowing cold air but running, there is a problem in your AC system that needs to be fixed. The exact problem depends on whether the AC is blowing warm air or no air at all. If there is no air getting through the system, there may be a blockage somewhere or a bad blower motor. If air is getting through but it’s not cold, there is another issue.

Before you try to figure out what’s going on, it’s a good idea to turn off the AC. Letting it run while there’s an undiagnosed issue could lead to bigger problems. That might mean even more complicated and expensive repairs. After turning off the AC, you can do some troubleshooting. Keep in mind that in the majority of cases, the best course of action is to call a professional to diagnose and repair the problem.

Diagnosing the Issue

The first thing to check is if your thermostat is working properly. Sometimes, it accidentally gets switched from the Cool setting to the Fan or Heat setting. This can make the AC blow air that never gets cold. You can also check to make sure the temperature is set to a temperature that’s lower than the ambient temperature in your home. This means that, if it’s 78 degrees in your home, for example, the AC won’t kick on if it’s set to 78 or higher. You would have to lower the temperature on the thermostat for the AC to start blowing cold air.

If the thermostat is on the right setting and temperature, the next thing to check is your air filters. Air filters need to be cleaned or changed about every three months. In houses with furry pets that shed, the filters may need to be cleaned or changed even more often. The same is true for homes located in areas that get a lot of dust or pollen.

When the AC filters are too dirty, air can’t flow easily through the AC system. Filters that are clogged with dust, dirt and other debris can burn out the motor.

Another possibility is that your AC system has a refrigerant leak that is lowering its ability to cool your house. If you take a look at your outdoor AC unit, you may spot other symptoms of this problem. These symptoms include ice on the evaporator coil or the refrigerant lines, or an unusual whistling or hissing noise.

There are several other possible causes of an AC that won’t blow cold air. One is a thermostat that isn’t working or needs new batteries. Another is a dirty condenser unit. The condenser is the outdoor AC unit, and its coil includes a lot of tiny metal “fins” that can get clogged with leaves, grass, dirt and other debris. If the condenser coil is clogged, it can’t do its job of cooling your home on a hot day.

Yet another possibility is a broken part somewhere in the system. Your AC is made up of multiple parts that are interconnected, including the indoor and outdoor units that both have several internal components that can go bad. If the compressor’s capacitor breaks, that can lead to a loss of cool air blowing from the system. Even holes or tears in the AC’s ductwork can lead to less cool air being pushed out of the vents.

If your AC is running but not blowing cold air, the best thing to do is to contact an HVAC repair specialist. An AC professional will be able to conduct a thorough check of your entire system and all its components. They will be able to make an accurate diagnosis of whatever is going wrong. In most cases, they will be able to fix your AC problem on-site.

A reputable HVAC specialist can also help you head off problems in the future by scheduling regular AC maintenance checks. These yearly or semi-annual checks extend the life of your AC by keeping it running at peak efficiency. This saves you money over time by preventing costly repairs that could result from small problems getting bigger over time. Regular AC maintenance performed by a professional also keeps your utility bills lower, saving you money in the short and longer-term.

Common Dirty AC Filter Symptoms

Changing your AC filters or cleaning them is a simple job that most homeowners can easily do on their own. This task can easily slip your mind as a homeowner, but it can cause problems. There are several dirty AC filter symptoms that you may notice when your filters need cleaning or replacing. Keeping up with this maintenance task will help keep your AC running well and extend its life over the long term.

Common dirty AC filter symptoms include the following:

  • AC filters that look dirty. Air passes from the room through the filter into the open space behind the filter that connects to the ductwork. When an AC filter is dirty, it’s usually easy to see a brownish-gray layer of dust, fine dirt, pet hair and other debris on the side of the filter that faces the room.
  • Noises like whistling coming from the AC when the system is on and blowing. This AC noise is the sound of air being forced through the dirty filter. When the filter is clean, the air is able to move through much more easily, and therefore much more quietly.
  • Vents that look dirty. Just like with dirty filters, it’s usually easy to see dirt and dust if it starts building up on the vents in your home. If you see more dust starting to build up, either on the vent or the metal grill that covers the AC filter, it’s a sign that the filters need cleaning.
  • Rising utility bills. When your AC filters are dirty, air has a harder time moving through them. This forces your entire AC system to work harder to push the air through. You’ll see this extra stress placed on your system reflected in your monthly electricity bill. The harder your AC has to work to cool your home, the more electricity the system consumes.
  • Your home isn’t cooling as much as it should. Dirty AC filters put stress on your AC system and cause it to not work as efficiently. This results in less cool air being blown through the vents into the rooms of your home.
  • The AC shuts down or cycles on and off too frequently. Clogged, dirty filters can cause the AC to overheat. This in turn could cause the whole system to shut down. You might also notice that the AC seems to be cycling on and off a lot more than normal.
  • Frozen coils on your evaporator unit. The evaporator coil is responsible for absorbing the warm air inside your home, so it can cool the air down and send it back through the vents into the rooms of your home. There is condensation in the coil that can freeze if the AC filters are clogged, blocking the coils from absorbing the home’s warm air.

AC filters should be cleaned or replaced every three months to avoid causing problems like an overheating system or frozen evaporator coils. If your home is extra dusty or you have pets that shed, you may need to change your filters even more often. This is especially true during the summer months when you use your AC the most.

an outside ac unit

How Long Should AC Run Before it Shuts Off?

Sometimes, people notice their AC seems to be cycling on and off either more or less frequently than usual. In some cases, this is normal; in others, it signals a problem. If you’re wondering how long your AC should run, keep in mind that it can vary depending on the temperature outside. It also varies depending on the target temperature you set at the thermostat.

As a general rule of thumb, the AC should run for about 15 to 20 minutes at a time before shutting off. There are several factors that can make the AC run for longer periods, even if it is working normally.

When it’s warmer outside, for example, your AC will run longer as it works to cool the house down to the temperature you set. This is even truer if it’s humid outside. The AC doesn’t only lower the temperature indoors, it also dehumidifies the air. When there’s a lot of moisture in the air, it takes longer cycles to draw out the humidity.

Sometimes, people have AC units that are the wrong size for their home. If your AC is too big for your home, it will run for shorter periods because it doesn’t take long to cool down the space. This might sound like a good thing, but it’s not. Since the AC also works to lower the humidity inside your home, shorter cycles can mean it stays overly humid indoors. An AC unit that is too small for your home will do the exact opposite—run for longer periods as it struggles to cool the large indoor space.

There are other factors that can make the AC run for too long or not long enough. Having your air conditioner inspected by a licensed, reputable HVAC specialist is the best way to diagnose AC problems and efficiently solve them.

ABC Can Diagnose and Fix AC Problems

It can be quite alarming when you hear strange noises coming from your air conditioning unit. If you’re concerned about your AC unit, contact ABC Home & Commercial Services. Our licensed professionals can provide any needed AC repair and are available all day and all night.

Tom Riggs

Tom Riggs is the Division Manager for Mechanical Services, overseeing sales and operations for HVAC, Plumbing, Electrical, Appliance Repair and Water Quality for all ABC Austin branches. He joined ABC in 2014. Before ABC, he was an HVAC Service Technician, HVAC Comfort Advisor/Sales and Operations Manager. Tom attended Universal Technical Institute. He's an avid outdoorsman and enjoys country living with his wife and two sons.

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