A bad thermostat in your home can make your AC malfunction. At first, the problem may seem to be with the air conditioner itself, which can lead to a lot of stress if you think you need a major repair or even a full replacement. Fortunately, the thermostat is a relatively quick and inexpensive fix. The following can help you determine if the thermostat is the problem.
Sign #1: The AC runs constantly
Does your AC tend to run constantly, or is the house cooling down to a temperature much lower than your thermostat setting? If so, then the thermostat is malfunctioning and no longer reading the room temperature correctly. Experiment by turning the thermostat up to see if that causes the AC to turn off. If it does, you may be able to limp along for a few more days with the broken thermostat until you can schedule a service call.
Sign #2: The AC won't come on
Sometimes the opposite occurs and the air conditioner will not come on. First, try turning the thermostat down all the way to see if this causes the AC to pop on. If it does, the trouble is with the thermostat. Also, try turning the setting from AC to "fan only." If the fan will run without the AC, the problem could be with the condenser unit in the AC and not with the thermostat. Finally, if you have access to a multimeter, you can check to see if a non-digital thermostat is using electricity or if it has shorted out.
Sign #3: Hot spots
Is the air coming out of the vents as it should, but it feels warmer than it should, like perhaps only the fan is running and not the air conditioner? This could be due to a thermostat that is running the fan even though you have it on the AC setting. Unfortunately, there is no way to verify that this problem is solely in the thermostat without bringing in an HVAC contractor to check both the AC unit and the thermostat. Often, though, this occurs because of a short in the thermostat, which means it will be a quick and simple fix.
Don't limp along with a possibly broken thermostat. Your HVAC tech can replace the thermostat with a new model. Consider getting a programmable thermostat so you can also better management your energy usage and electricity bills. For more information, check out websites like http://calldoctorfixit.com.