Window air conditioner common questions

These common questions about window air conditioners are the ones our experts hear the most often from our customers. You might also find the help you need by checking the common symptoms and solutions for window air conditioners. When you’re ready to make a repair, search your model number to find replacement parts. Sears PartsDirect has the part you need, no matter where you bought your window air conditioner.

Why won't the air conditioner turn on?

Check the power cord, which usually has an over-current detection device. If the over-current detection device is tripped, reset the device and see if the air conditioner powers up. Check the electrical outlet to make sure that it is working. Check for a tripped house circuit breaker.

What size window air conditioner do I need?

The size of the window air conditioner needed depends on the size of the room you wish to cool, how well the house is insulated and the number of windows in the room. Measure the width and length of the room and multiply those numbers to determine the square footage. For a room that's less than 150 square feet, a 5,000 BTU air conditioner is the proper size. For every 100 additional square feet over 150, add 1,000 BTUs of cooling capacity. Units are generally available up to 26,000 BTU; however, the larger the unit, the heavier and less energy-efficient it will be.

What is a BTU?

BTU stands for British Thermal Unit and is defined as the amount of air needed to cool or heat 1 lb. of water by one degree. Window air conditioners are rated for BTU output. When choosing an air conditioner, pick the model that has a high enough BTU rating to properly cool the space where it is installed.

Where should I install a window air conditioner?

Window air conditioners should be placed in areas of the home that are used most frequently, including the kitchen and living areas. It's usually better to have multiple smaller units rather than one large unit if possible, so you can decide which areas are cooled and keep energy costs lower. If you can only choose one location for a window unit, the bedroom might be the best spot. It's difficult to sleep when it's hot and humid, and having a window unit in the room helps.

Is it normal for water to drip from the window air conditioner?

Yes, many window air conditioners are designed so that water drips from the outside base of the unit. 

The humidity that the window air conditioner removes from the room collects on the evaporator fins and drips down to the base pan inside the cabinet. The water then drains out of the base of the air conditioner cabinet to the outside of the home.

Why is ice building up on the coils behind the air filter?

A number of factors can cause ice to build up on the coils of a window air conditioner. Dust, dirt or debris can clog the fins and coils, restricting air flow through the unit and making the compressor to work so hard that it lowers the coil temperature below the normal range in an attempt to make up for the lost cooling power from the blocked coils. A dirty air filter has a similar effect.

Another potential cause is setting the desired temperature very low, which causes excess condensate to build up on the coils, further lowering the temperature of the coil and leading to icing.

Low fan speed for an extended period can also cause icing on the evaporator coils behind the air filter.

Why is water leaking into the room from the air conditioner?

An improperly installed window air conditioner can leak water into a room. The outside edge of the unit should be slightly lower than the inside edge so the water drains outdoors instead of inside.

A clog in the drain pan where condensate collects during operation also could cause the water to leak inside the room.  

Another reason is that warm moist air could be leaking from outside the window into the air conditioner case, where the moisture in the air condenses and drips inside the room. Seal air gaps with expansion foam to remedy this problem.

Why does my window air conditioner short cycle?

Several conditions cause the compressor to turn on and shut off at short intervals. The thermostat or temperature sensor could be faulty or obstructed. Leaking refrigerant and icy coils can also cause short cycling. Installing an air conditioner that is too large for the space being cooled is another cause of this problem.

How do I add refrigerant to my window air conditioner?

Adding refrigerant to your window air conditioner is not a do-it-yourself repair. Recovery and recharge of air conditioner refrigerant is tightly regulated by the Environmental Protection Agency (EPA). You shouldn’t need to add refrigerant unless a refrigerant line is leaking. Only an EPA-licensed technician should recover, repair a refrigerant line leak and recharge a sealed refrigerant system in your air conditioner.

Is it hard to install a window air conditioner?

Most window air conditioners can be easily installed in 15-20 minutes. All window air conditioners include an installation kit and instructions. Simply follow the manufacturer's instruction for installation and then just plug it in.