It's hard to resist the urge to crank up the AC during a heatwave. But if you rely on a window unit to stay cool, you may notice that when temperatures soar, your AC isn't as effective as usual, and may even cut out altogether from time to time.
The cause could have nothing to do with your window unit—in the past, you've probably received messages from your local electricity supplier about conserving energy and possible outages during a heatwave, and if your window unit is suddenly not keeping you cool, that could be why.
Asif Bux, the service manager at Comfort Union, a full-service HVAC and plumbing company, says it's a question he deals with a lot: Is it a power issue, or is my AC failing?
According to Bux and Brad Roberson, president of Aire Serv Heating & Air Conditioning and an expert in HVAC and indoor air quality, some common signs that your AC window unit might be dying include:
It stops blowing cold air (or the air is not as cool as it used to be)
It's making loud, unusual noises (e.g. grinding or buzzing)
It's leaking water
It's frequently switching on and off
You're getting unusually high energy bills, even accounting for regular AC use (a sign of reduced efficiency)
Before writing your current AC window unit off completely, do some detective work to figure out if it's actually broken, or there's something else going on.
According to Roberson, AC window units are designed to lower temperatures by a certain amount, and sometimes the heat becomes too much for them. "During times of extreme heat and extended use, the unit may struggle to achieve or maintain desired temperatures," he says.
Power supply issues might also be to blame, Bux says—especially during peak usage times, when the electrical grid could experience voltage drops. "Dimmed lights or other electrical anomalies can indicate a grid issue," he says.
If the unit functions properly again when outdoor temperatures cool down, you'll know it was likely a heat-load or electrical grid issue, Bux says.
The first thing to check is your unit's air filter. These get dirtier quicker than you think they will, and can reduce cooling efficiency, Bux says. A filthy filter can also cause your unit to cycle on and off frequently.
Check to make sure the coil fins—located on the part sticking outside of the window—aren't bent and/or folded over, which will restrict airflow, Roberson says. While you're back there, clean off any dirt or debris on the coils, which Bux says can "impeded heat exchange." Frost buildup is another sign clogged condenser coils, he says.
Make sure the outside part of the window unit isn’t blocked by anything that would reduce airflow, Roberson says.
Check the condensate drain to make sure it's not obstructed and operating properly, Roberson adds.
Check the unit's thermostat settings. This sounds obvious, but maybe you forgot that you set it to "low" at night and forgot to set it back to full capacity during the day. Bux also recommends making sure the power supply is adequate by checking the breaker panel and inspecting the power cord.
If your AC unit is switching on and off frequently, Bux says that it could be a sign that the unit isn't powerful enough to cool the room or space that it's in. One way to find out if this is the case is to check the BTU rating and ensure that it's high enough for the square footage of the room.
If you've checked all of the areas mentioned above and you're not in the middle of a heatwave, your AC window unit may actually be broken. "The unit may have a problem with the compressor, or refrigerant levels may be low, or there is a refrigerant leak," Roberson says. Water leakage can stem from a failing gasket, Bux says, while unusual noises—like buzzing or grinding—may be the result of loose components, a failing motor, or electrical issues.
In short, it comes down to the age of the AC unit. If it's more than eight to 10 years old, it's usually less expensive to replace the unit because parts to fix it may be harder to find, and it may use outdated, less-energy-efficient technology, Roberson says.
For newer AC window units, Bux says that if repair costs exceed 50% of a new unit's price, you're better off replacing it—especially considering the likelihood future repairs. Plus, because new units are more energy efficient, you'll likely save money on your electricity bills.
