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Reasons That an Air Conditioner Will Not Come on

Lee Morgan

As the sweat trickles down your forehead, you may be staring at your thermostat wondering why the air conditioner is not coming on. You wait for the system to kick on, but there is nothing but silence. On a hot day you’ll want answers fast, so start with the obvious things and work your way through a list of common reasons why an air conditioning system will not come on at all. Odds are you will discover the problem quickly and have it up and running.

Thermostat Settings Wrong

Sometimes you can underestimate the temperature in the house. The house may be much warmer than you think it is. If you have a digital readout, the thermostat should tell you how hot it is in the room at the moment. Set the desired temperature lower than the current temperature. If the current temperature is 77 degrees and you have the thermostat set to 78 degrees, it’s not coming on until the mercury climbs a bit. Try turning your thermostat down several degrees to see if it kicks on within a minute or two.

Power Turned off

One factor that is certain to keep your air conditioner from running is a lack of electricity to the unit. If a circuit breaker has been tripped, you’ll need to turn it back to the “on” position to get your system up and running again. A power switch is also located on the air handler, usually found in a closet somewhere in the home that may have been bumped to the "off" position. Another service shutoff switch is located on the exterior of the house near the outside portion of the central unit. It must be turned on as well. Any of these will keep the current from reaching the system.

Broken or Burnt Wiring

Broken, frayed or burnt wiring can prevent proper function of an air conditioner. It can also be the source of an electrical smell and potentially be a fire hazard. Shut off all power to the system if you find faulty wiring, and get a professional electrician to repair the wires before starting the system back up.

Lock out or Reset

Overheating caused by clogged air filters or other factors can cause an air conditioner to shut down and even go into a lockout mode. This safety feature makes turning the system back on possible until the reset button on the outside unit is pressed back in. It may also require the breaker to the system to be turned off for a minute and then turned back on for proper functioning.