How to Troubleshoot a Window Air Conditioner Unit

A hot summer day is no time to find out your air conditioner is on the fritz, but that's when it usually happens. Luckily, most air conditioner problems are easy to solve. Those that aren't usually require professional assistance, and that isn't because they are beyond the purview of a savvy do-it-yourselfer. You need a licensed pro to recharge the unit or make modifications to the refrigeration system for three reasons: The first is to protect the warranty, the second is to protect yourself, and the third is that federal law, as overseen by the Environmental Protection Agency, requires it. You can often fix electrical problems, leaks and some issues that cause inefficient cooling yourself, though.

Bright, airy, air-conditioned room.
credit: Breather
Size your air conditioner properly to ensure it does its job without blowing a breaker.

Electrical Problems

When your air conditioner won't start up, the first thing to do is check the outlet. If it doesn't have power, the breaker in the main panel or a GFCI outlet on the circuit may have tripped. All you need to do is reset it, but if it trips again immediately, that means something is wrong in the circuitry.

Try plugging the unit into another outlet, using an extension cord, if necessary. If it works, you've got a problem with the outlet or the circuit wires. If it trips the new outlet, the issue is the internal circuitry in the air conditioner. The problem could be a blown or dirty fuse, a bad capacitor or loose wiring, but the unit could also be working too hard and overheating. That's usually a sign that the air conditioner is too small for the room it's supposed to be cooling.

Sizing Your Air Conditioner -- The cooling capacity of an air conditioner is measured in British Thermal Units (Btu)/ hour, and units range from 5,000 to 20,000 Btu. To determine the size you need, you usually measure the square footage of the room and multiply by 20 Btu. You may need to add 10 percent to this number if you have high ceilings or the room is sunny. Additionally, you should add 600 Btu for every person above two who occupies the room, and you should up the figure by 4,000 Btu if you're cooling a kitchen.

Leaking Water

Window air conditioners are designed to drain to the outside of the building, but to do this, they have to be installed with a slight incline toward that direction. If your unit leaks onto the floor, check the slope, and adjust it if it's horizontal or leaning into the room.

A leaking unit that has the proper slope toward the outside of the building probably has a clogged drain outlet. You may have to go outside to unclog it. It's also possible that the interior drain hose is plugged. You can service this yourself, using your manual to guide you to the hose.

Condensation Leaks -- Some leaks are caused by the formation of water droplets at the point at which the air conditioner passes through the window. This happens because the air inside is cooler than the air outside, and water tends to condense from the cooler air. Correct this problem by insulating the gap between the air conditioner and the opening with weather stripping.

Inefficient Cooling

If your air conditioner doesn't blow cold air, you may need to recharge the refrigeration system or repair the condenser, but before calling a pro to do either of these jobs, look for a couple of other problems. The first is a dirty air filter. When the filter is dirty, air can't circulate around the cooling coils. As a rule, it's a good idea to clean or change the filter once a year. While you're at it, clean the coils. Dust on the coils is another reason for inefficient cooling.

Another problem that's easy to fix yourself is ice on the coils. Icing over often occurs in cooler weather when the condensation that naturally forms on the cooling coils doesn't drain properly and ends up freezing. Paradoxically, a layer of ice on the cooling coils impedes their cooling ability. If the coils are iced over, you can usually see the ice on the coils when you remove the filter and look through the air inlet. The remedy is simple: Turn off the unit, and wait for the ice to melt before turning it back on.

A unit that ices over repeatedly or does so in hot weather may not have enough refrigerant, and the reason could be that the system is leaking or the condenser isn't functioning properly. If so, you need a pro to make the repair.

Air Conditioner Won't Turn Off -- Inefficient cooling is the primary reason for a failure of the air conditioner to turn off. Because of the failure of the unit to cool the air, the temperature in the room never reaches the target temperature, and the air conditioner runs constantly. Clean the filter; check the coils for ice, and call a pro if you suspect a refrigerant leak or a problem with the condenser.

Chris Deziel

Chris Deziel

Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience, and he is also an avid craftsman and musician. He began writing on home improvement topics in 2010 and worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. He currently contributes a monthly property maintenance blog on A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at