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Why Won’t My AC Turn On?

Posted on: February 21, 2019

Restarting an air conditioner or heat pump when it doesn’t respond to the thermostat can restore comfort to an increasingly warm home. Sometimes A/C systems stop when parts fail, while other times it’s an interruption in the power supply that prevents them from starting.

Troubleshoot the Thermostat

The thermostat controls when the air conditioner turns on and off. Make sure that it’s set to “cooling” and “on.” Turn the temperature down a few degrees to see if it will start. If yours is battery-operated, it may need new batteries.

If it still won’t turn on, it may need cleaning. Carefully remove the housing and gently brush away the dust. Replace the cover. If cleaning doesn’t help, you may need a new thermostat.

Circuit Breakers and Fuses

When the thermostat appears to be working, check the power at the circuit breaker. Sometimes breakers will trip for no apparent reason. If resetting doesn’t start the air conditioner, look for a light switch by the air handler or inside it. HVAC contractors sometimes install a switch nearby to simplify turning it on and off.

The problem might be the fuse found inside or near the outdoor condenser. Look at it carefully to see if it’s intact. If not, contact us immediately for a replacement and to investigate why it blew.

Air Filters

A switch activates when the volume of air flowing through the air handler is too low, almost always caused by an overly dirty air filter. Check the filter and replace it if necessary. Make a note to check the condition of the filter monthly during the summer to prevent triggering the switch. Check the filters monthly during the cooling season and change it when it’s covered with dust.

Evaporator Coil

The evaporator coil may be frozen. Low refrigerant or a dirty evaporator coil can freeze the coil over and activate a switch that shuts the A/C off. It won’t resume running until the coil thaws. The safest way to thaw the coil is to turn the fan to “on” instead of “auto” until the frost melts. Call for service to check the refrigerant level or clean the coil.

Find the Drain Pan

This pan sits at the bottom of the air handler and collects the water that condenses on the evaporator coil. Your system may have a float that shuts the system off if the water level in the drain pan gets too high. This switch prevents flooding that can damage the nearby surfaces and materials. You may need to hit the reset or “on” button for the A/C, which you’ll probably find inside the air handler. Our technicians can test and diagnose electrical problems.

Electrical Problems

More often than not, your air conditioner could have bad electrical components when it just won’t start. These parts might make ticking or clicking noises as they begin to fail, or they may be completely silent. One part that will fail silently is the contactor, which sends power throughout the system. There are many others that will keep the A/C from turning on that we can test and diagnose.

Bottom Line

Troubleshooting your air conditioner could get it back online quickly, as long as the problem is relatively easy to diagnose and fix. Many times, all it takes to prevent a breakdown is regular maintenance, like battery and air filter changes. Other times, you’ll need a pro from SM Air to get your system running smoothly.

Contact SM Air online or give us a call at (512) 212-4777 to schedule AC repair services in San Marcos, TX.