The hum of the AC turning itself on is a classic summertime sound. Air conditioning keeps your house cool by turning on when it reaches a set temperature, and then turning itself off again after the house has cooled off.
On a blistering hot day, your AC may well be running longer than usual to keep your house cool, but if it's a normal day and your AC is still on---or worse on and not cooling your house, it's something to worry about. Here are a few reasons your AC could be running longer than usual, and how to fix it.
One of the most common reasons for an air conditioner to start running longer is due to an air filter that is clogged with dust. Air filters need to be changed a minimum of once every 3 months. If the air filter is too full, the air conditioner will have to work for longer in order to cool the home.
If the air filter is full, try changing it and see if that helps.
Another reason your AC may have to work longer to cool your home is that it isn't getting the air flow it needs. The AC works by pulling warm air into the machine where it cools the air off, and then pushes it into your home. If the air conditioner can't get enough air to pull in, that also means it can't push enough air out, leading to a warmer home.
Just as the air conditioner needs to be able to take in enough air to function properly, it also needs to be able to push the cool air out unrestricted. If a piece of furniture is blocking the way, this can prevent the cool air from reaching the rest of the house.
Make sure none of the registers are blocked so cool air can pass through the house unrestricted.
Sometimes the problem is caused by maintenance that needs done on the machine itself. If you notice ice on the refrigerant line, a hissing coming from the AC, or dirty components there may be something wrong with the AC itself that needs taken care of by a professional.
Many of the things that could be wrong, such as a refrigerant leak, are unsafe for untrained people to try and repair, so this should definitely be handled by a professional.
If the machine is working fine, it's also possible that the air conditioner is simply too small for the area it is trying to cool. If this is the case, you may need to get a larger air conditioner to properly cool your house.