Q. My air conditioner isn’t running at all and it was working fine. What can I do?

A. First, check the room thermostat temperature setting. Set it 5 degrees below the room temperature. Sometimes it’s as simple as the thermostat not being set properly. Another item to check is whether the thermostat is set to “cool” — not “off” or “heat.” If it’s not set to “cool,” it is simply turning off the air conditioner.

Q. My thermostat is set properly, but the air conditioner still isn’t running. What next?

A. Check to see whether the electricity is on for the equipment. Check any service switches, including outside by the compressor, inside at the air handler and fuses or circuit breakers in the electrical panel.

Q. I’ve tried all of those. Still nothing. What else should I check?

A. Check the outside air conditioning compressor. If it’s not running, be sure that the outdoor service switch and the indoor power switch, fuse or circuit breaker are all in the “on” position. Check the indoor air handler. If the indoor blower unit isn’t running, be sure that the electrical power switch at the furnace or air conditioner air handler is in the “on” position. Sometimes there’s more than one switch, such as one right at the unit and another at the entry to the room where the equipment is located, or even upstairs on a higher floor if your air handler is in a basement or crawl space.

Q. All of the electrical system and switches are OK. I’m still not getting cool air. What else?

A. Check the air filters to see that they have not become blocked with dirt and debris. Usually, the air filter is right at the air handler or blower unit, or your air filter may be installed behind a grille covering a central warm-air return. Also, check the air supply registers in ceilings, wall or floors where cool air is supposed to be delivered to various rooms. Be sure they are in the “open” position and aren’t blocked.

Q. I’ve done all of these and there’s still no cool air flowing. What next?

A. In this case, you probably need to call a service technician.