Three reasons your AC may not turn on

One of the most common questions we get is, “Why won’t my AC turn on?” Typically this means the outside unit isn’t coming on. But sometimes, a homeowner reports to us that the thermostat itself appears to have gone blank.

Whatever it looks like, an AC unit that won’t turn on might indicate a larger issue. Here are some reasons that could be happening, and what you can do about it.

Thermostat settings

Always start with the simplest solution first! If your thermostat is working, but the outside AC unit won’t turn on, check to see if it’s set to ‘”cool” or “auto.” You might see that the thermostat is set to “off.” This is one of the first things a technician will investigate—you may as well check it yourself before investing time, energy and money into a repair call.

Another thing to check is the temperature your thermostat is set at. Your set temperature should only be 3-5 degrees below the current temperature if you want your system to cool your home.

Electrical circuit issues

First, check to see if the breaker for the outside unit has tripped. If it has, you can reset it. Another place to check is the electrical disconnect for your outside unit, which will usually look like a small metal box mounted near the outside unit.

This box is an external means of disconnecting the power, and usually has a small fuse inside. If the fuse is blown, you can replace it with an identical fuse.

If replacing a fuse or returning the breaker to the “on” position fixes the problem, but only temporarily, then you may have other underlying electrical issues. That’s a good sign you should call a professional.

Is your outside unit or coil frozen up?

Many of the middle and all top tier HVAC systems have some built in safety features, which are designed to ‘shut down the system’ to prevent further damage until the problem(s) can be corrected. If your unit is freezing up, it’s probably a symptom of a larger issue. Here are some of the most common.

Your air conditioner is a little like your car—it’ll let you know if there’s an issue. If your check engine light is on, that could mean a few different things, but it does mean you should get it checked out.

Most air conditioning units will shut themselves off for a reason—if there’s an issue with the unit. Not all of them are difficult or expensive to correct, but it could be catastrophic if a long-term issue is left unaddressed.

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