A constantly running air conditioner can lead to all sorts of problems. Not only is it wasteful in terms of energy consumption, but the constant running can also prematurely wear out and damage the parts in your AC, leading to expensive repairs or premature unit replacement in the future.
The most obvious symptom is that the fan is always running. The AC simply never powers off. Sometimes there may be no cool air coming out of the vents, but yet the hum of the fan motor will still be heard.
You may not notice the problem at first, especially if it is hot or if you aren't home often. In this case, the first symptom you notice may be elevated energy bills. A constantly running fan can use a lot of electricity, so a bill increase will usually be noticeable during the first billing cycle after the problem begins.
There are three main causes for a constantly running AC. The most obvious is that the fan setting on the thermostat is set to continuously run, or that the thermostat has malfunctioned so that it isn't registering that the fan is not set to continuous operation.
Another common issue is the compressor contactor, which is in the outside AC unit. If it becomes stuck, it will no longer relay the shut off of the fan from the thermostat to the compressor. The fan will continue to run.
The third issue may be with the wiring itself, namely that which runs from the indoor thermostat into the exterior unit. These wires should be wrapped and tucked away to protect them from exposure, but time and weathering can lead to issues. Wires can become exposed, such as from being hit with a string weed trimmer, and damaged. If this happens when the fan is running, then it may continue to run after the connection to the thermostat is severed.
All of these common issues are repairable. Adjusting the thermostat to the proper setting or replacing a faulty thermostat will often fix the issue. If the wires are at fault, they will need to be inspected so the damage can be found, and then the unit can be rewired.
If the contactor is damaged, then it must be replaced. When it is only stuck, your contractor can usually loosen it and get it working again. Cleaning and lubricating the unit will prevent it from becoming stuck in the future.
Contact an air conditioning systems repair contractor for more help with a constantly running AC.