In addition to their major components, air conditioning systems have many smaller parts that all work together in generating and circulating cooled air. Among these myriad switches, valves and tubes is the limit switch, a small safety device that every homeowner should know about in the event of a performance problem.
So, let’s delve deeper into what an AC limit switch does.
Have you ever seen a treadmill that has one of those plastic key cards inserted into the console, with a stretchy strap on the outside end? Pull that piece of plastic out, and the treadmill doesn’t work. When you were a kid, did you ever try to open the door on the fridge just a bit to see if the light stayed on when you shut the door? Of course it doesn’t, because there is a switch in there that turns off the light when the doors is closed.
In effect, those two devices are limit switches – they kill the power to the machine when a certain condition has been reached. If you start to fall off the treadmill, the plastic key falls out and the motor shuts off. When the refrigerator door is shut, the light shuts off.
Your air conditioner has a similar device, which tells it when to shut off after the air has been cooled enough. In this way, the limit switch is the way that your thermostat and air conditioner communicate. When the inside temperature reaches the target temperature you have set, the thermostat activates the limit switch and turns off the AC. When the temperature rises, the limit switch turns the power to the AC back on.
The most common symptom of a problem with the limit switch is that the AC will short cycle, turning off too quickly. Or sometimes, it may not turn off or on at all. This may mean the limit switch is stuck or that the wiring has gone bad. In any case, you should call for repairs.