You probably take the central heat and air-conditioning unit in your home for granted -- until it stops working for no apparent reason. Not every problem with a central heat and air system leads to a significant repair bill. Small things can go wrong and cause the entire unit to shut down. Basic troubleshooting can help you locate the issue. Once you know what is wrong, you can determine the necessary course of action to get the system back up and running.
Examine to setting on the thermostat. Check the "Heat/Cool" switch to see if it is set correctly. For example, if the heat is not coming on, does the panel indicate the system is set to heat?
Raise or lower the thermostat setting to trigger the system. For example, to test the heat, move the thermostat to a high temperature such as 85 degrees Fahrenheit. To test the cooling system, turn it down very low. Wait five minutes to see if the system comes on.
Open the circuit breaker panel, and locate the breaker switch for your central unit. Most circuit panels have a list or display inside the panel door that helps identify what each breaker switch controls. Check to see that the breaker is in the "On" position. If it is "Off," flip the switch back to "On." If you have an older electrical panel, look for a burned fuse and replace it if necessary.
Move to the control unit for your system. This is what most people refer to as the furnace. Many systems have an "On/Off" switch either on the unit or nearby. It might look like a light switch. Once you locate it, flip it off and then back on. Wait five minutes to see if the system begins to run.
Turn the shutoff valve on a gas system counterclockwise; if the handle does not budge, the gas is turned off. You should see a valve near the furnace that controls the gas flow. Turn the valve clockwise if the gas is off to allow flow to the system. Check for a similar valve near the gas company meter.
Walk outside the house, and locate the outdoor air conditioning unit. Central air systems have condensers outside the house. Clear any debris around the air conditioner. Leaves and tree branches can block the flow and cause the unit to malfunction.
Call the utility company to see if there is a problem with your account or if there is an outage in the area. Discuss the system problem with a service technician at the utility company. They might have suggestions on what could be causing the issue or arrange a service call.