Troubleshooting a Window Air Conditioner

In hot, humid climates, air conditioners are practically survival tools. I found that out during a recent trip to coastal Mexico, where the temperature consistently stayed above 90 F (32 C) during the day and 80 F (27 C) at night, and the humidity seldom dropped below 90 percent. There are plenty of places in the U.S. that experience similar conditions in the summer. If you live in such a region, you know the importance of keeping your air conditioner in good working order. Not only does it keep you cool, but it also dehumidifies the room you’re in, which can be a real life-changer in humid environments.

Mini-split and central cooling systems that use heat pump technology are common in places where heat and humidity are endemic. Still, people who live in climates that only occasionally experience extreme heat and humidity often choose window air conditioners instead. They’re less expensive than heat pumps, and they don’t require professional installation.

Like all appliances, window air conditioners are bound to have glitches from time to time, and some are easier to troubleshoot than others. Here, with the help of HVAC experts Melanie Powers, Glenn Gault, Hugh Williams and Anthony Smith, we cover some of the most common problems — and solutions.

The Air Conditioner Won’t Turn On

The solution to your problem might be really simple. “It could mean an issue with the thermostat,” says Powers. “Try resetting it to see if it will turn back on.”

Count yourself lucky if that’s all you have to do. Most other problems are a little more complicated:

Electrical Issues

A window air conditioner plugs into a receptacle, so if the unit isn’t getting power, check the breaker. “The most common cause of an air conditioner not turning on is a tripped circuit breaker,” advises Gault. “It often happens after heavy storms or after the use of many high-powered appliances at once.”

If the breaker hasn’t tripped, check the receptacle. If it’s a GFCI, it may have tripped. That can also happen during a storm or sometimes even in conditions of excessively high humidity. Push the reset button on the receptacle (the bottom one) to restore power.

Drainage Issues and Leaks

Gault suggests checking the drain pan. “Your AC might not be turning on due to water buildup in the drain pan. Make sure to empty the drain pan and clear the drain line—clogs in the drain line are the most common cause of water buildup.”

He continues, “In some cases, the AC is not turning on because of the leaks in the coolant lines, especially near the compressor. Such leaks lead to a frozen coil, which doesn’t allow the AC to start working.”

You can thaw the coils simply by leaving the unit off for a day or two, but if there’s a refrigerant leak, they’ll freeze again. If this happens, you need to call an HVAC tech with EPA refrigerant repair certification to fix the leak and recharge the refrigerant.

Malfunctioning Components

The internal component most likely to prevent an AC unit from turning on is the capacitor, which is a device that stores charge to give the compressor the extra “oomph” it needs to switch on. “You’ll know the capacitor is the problem if the outside fan isn’t running or the outside unit is buzzing but not spinning,” says Gault. Replacing a capacitor is a simple job, but it’s a dangerous one because it could discharge while you’re holding it. If you don’t know how to safely discharge a capacitor, call a service tech for help.

A number of other internal problems can prevent an AC unit from turning on, including disconnected wires and worn bearings. These usually don’t crop up until the unit is well-used and needs replacement.

The Unit Doesn’t Blow Cold Air

As indicated above, a refrigerant leak can cause a lack of cold air. “Low refrigerant levels are often indicated by ice on the condenser fins and in the pan,” says Gault. You need a licensed service tech to fix this problem.

A more likely cause is reduced airflow caused by dirty filters. “An easy, cost-effective fix is to simply replace the filters,” says Williams. Smith adds: “Another possible reason is a dirty condenser. Since the condenser is the portion of your air conditioner that is outside and exposed to the weather, dirt and debris can easily become stuck inside of it. A blocked condenser will have to work considerably harder to draw in air and cool it.”

Gault recommends cleaning the condenser coils with a garden hose.

The Air Conditioner Is Leaking

Gault lists three main causes of leaks:

• Clogged drain line;
• Frozen evaporator coil;
• Cracked drain pan.

You can often clear clogs by vacuuming them or pouring vinegar into the drain pan and letting it sit overnight to dissolve them. If the coil is frozen, leave the unit off until the ice melts, and call a service tech if the problem happens again. A cracked drain pan is a repair for a pro, says Gault, because it often involves removing the coil.

Williams mentions one other possible cause of leaking: not having enough tilt due to improper installation. “From my experience, homeowners are scared by seeing their unit tilt downward, so they’ll try to keep it level. In doing so, however, the unit cannot drain properly and will leak inside their home.”

What If My Window AC Won’t Turn Off?

Your window air conditioner unit temperature is regulated by a thermistor or a thermostat. These sensors can occasionally fail. When they do, the air conditioner can’t read the temperature in the room, so it may continue running even after the set temperature has been reached.

On some models, you can test the continuity of the thermostat (or thermistor) the same way you would check a light switch and replace that part if it isn’t working. (Or, if this sounds like Greek to you, you can have an HVAC technician conduct this test.) On some models, however, the thermostat is part of the control panel and can’t be removed. In that case, it’s your call whether to replace the faulty control panel or simply buy a new air conditioner.

About the Experts

• Melanie Powers is the President and CEO of Goodberlet Home Services, an HVAC servicing company based in Chicago, IL.
• Glenn Gault operates Gault Heating & Cooling, an Ohio-based, family-owned business established by his father in 1955.
• Hugh Williams is a home improvement expert at Magic Windows, based in Woodbridge, Ontario.
• Anthony Smith is the Director at Midland Air Conditioning, based in the U.K. He has over 28 years of experience in the HVAC industry.