One of the most common explanations would be that the unit is running low on refrigerant. You may also have a thermostat problem or be dealing with a dirty air filter. Refer to the list above for more information about the other possible causes of an air conditioner blowing warm air.
The evaporator coils inside your indoor air handler unit play a vital role in your AC's ability to cool air. If they become clogged with dirt, debris, mold, or other contaminants, it can keep your AC from cooling properly, resulting in prolonged cooling cycles and blowing warm air throughout your home.
If your air conditioner is running, but not lowering temperatures inside, one issue could be a blocked or clogged condenser coil. When operating correctly, the condenser fan draws air into the outdoor unit through the condenser coil to pull heat energy out of your home.
Turning off the AC is usually helpful and sometimes required to safely investigate some of the possible issues with an AC system not cooling. If it's a thermostat setting that's the issue, it's not necessary to turn off the AC.
A dirty air filter
Your air filter is designed to trap contaminants in the air before it gets pulled into the AC system. But over time that means that your filter gets dirty and clogged. And if a dirty filter isn't replaced, it can seriously limit your AC's cooling power.
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Feel the Air
If there is considerably less air than normal coming out of the vents, or if the air is warm, there may be an issue. If the outdoor unit is running and there is no air coming out of the vents, this is also a problem. If this happens, your evaporator coils may be iced over.
Your air conditioner's internal circuitry needs some time to reset after you turn it back on. This can take approximately a half-hour, so sit tight for about 30 minutes. Turn your air conditioner back on at the thermostat. After 30 minutes have passed, turn your air conditioner back on at the thermostat.
Look for it first around on the exterior of your machine, especially along the bottom edge near the ground. An AC's reset button is typically red and visible, so it should be easy to spot. If you don't see a reset button on the outside, it could be located inside the unit behind the service panel.
Once you locate the isolator, you may turn it off and wait for 30 minutes. The time allows for the appliance to dispel electrostatic charge. After half an hour, you can turn the lever your AC should restart without a problem. Once your AC is on, test it to determine if it's working.
A good rule of thumb is during the hottest days when the dial reaches 100 degrees it is best to set your AC to somewhere between 75 and 80 degrees.
Ideally, your AC should run for 15 minutes on nice, warm days. Only on those rare triple-digit temperature days should your air conditioner be running almost all the time. If your AC isn't following this pattern, you could have a problem.
Most systems need Freon replacement anywhere from once every two to five years from a professional HVAC Contractor. The most significant exception to this rule is when there is a leak in the air conditioning system, which decreases the amount of refrigerant in an AC unit over time.
If the refrigerant levels are low, it cannot fully expand; therefore, it cannot create enough cool air. If you notice that the vents are blowing warm air, turn off the AC immediately because the coil will only continue to get warmer as the fan blows.
Here's how long some of the most common types of AC last:
Portable AC — 5-10 years. Residential single whole-home AC unit — 15 years. Central air-source heat pumps — 15 years (and up to 20–25 years if well-maintained and in a well insulated home) Ductless mini-split AC systems (heat pumps) — 20 years.
To reset mechanical thermostats, simply turn off the thermostat and flip the circuit breaker. This can be done by going to the breaker panel and turning off the appropriate breaker switch for 30 seconds. After turning the breaker back on, turn the thermostat back on and the thermostat should be reset.
Turn it Back On
After waiting for 1 minute, the AC unit will reset on its own.
Repeatedly starting and stopping an AC unit is also less likely to damage it than allowing it to run continuously for long periods of time. The strain may not have an immediate impact, but it can shorten the lifespan of your AC unit in the long run.
Weak airflow is one of the first signs that an air conditioner is on the fritz. You'll start to notice little airflow coming from the AC vents, which is a sure sign that the unit's compressor is failing or that your ductwork is clogged.
How Do I Check an Air Conditioner for a Blown Fuse? If you think your air conditioner has blown a fuse, the first sign you'll notice is that the outside AC unit is inoperable. The best way to check for a blown fuse is by using a voltmeter.