Brownouts and air conditioners

Brownouts—temporary drops in voltage rather than a full outage—can put real stress on a home air conditioner’s compressor motor. If you notice dimming lights, a humming or struggling AC, or a unit that won’t start during hot weather, the safest homeowner response is to switch the thermostat to “off” and unplug or de-energize the outdoor unit until utility power is confirmed stable, then have a licensed electrician or HVAC technician inspect the system before you run it again.

What a brownout actually is

A brownout happens when the utility grid is under heavy strain, usually during extreme heat when everyone’s air conditioner is running at once. Rather than cutting power completely, the utility (or the grid itself) delivers reduced voltage to slow demand. ENERGY STAR notes that this kind of “involuntary curtailment” or brownout tends to hit vulnerable populations, including children and older adults, the hardest, which is worth keeping in mind if you’re a landlord with tenants who rely on cooling for health reasons.

What to check

You don’t need special equipment to notice a brownout. Common signs include lights that dim or flicker, a TV or appliance display that dims, or an air conditioner compressor that hums but doesn’t start, then cycles off on its own protective controls. These are useful observations to report to your utility or an electrician, but confirming actual voltage levels with a meter, and diagnosing whether a compressor has been damaged, is electrical work—not something to test yourself with the unit running.

What to do while voltage is low

During a brownout or any power disruption, Ready.gov recommends disconnecting appliances and electronics to avoid damage from electrical surges, since power can return with a momentary spike. For an air conditioner, that means turning the thermostat off and, if you’re comfortable doing so safely, switching off the breaker to the outdoor condensing unit until you’re sure voltage has returned to normal. Leave it off longer than you think necessary rather than restarting it the moment lights come back on.

If you’re running a backup generator

Never wire a portable generator directly into your home’s electrical panel yourself. FEMA warns that backfeeding a generator into household wiring can send dangerous voltage back through power lines and injure utility workers, and recommends using a qualified electrician to install a proper transfer switch. The same source and Ready.gov’s generator safety guidance both stress running generators outdoors only, well away from windows and doors, because of carbon monoxide risk, and using heavy-duty rated extension cords rather than improvised wiring. For a closer look at sizing and using a generator for home cooling loads, see the generators section.

Installation and wiring

Record flickering lights, a compressor that struggles to start, and whether nearby houses have the same dimming. Voltage testing at the panel or disconnect, transfer-switch wiring, and compressor or capacitor checks involve energized equipment and belong with an electrician or HVAC technician.

Reducing your brownout exposure

Because brownouts are tied to peak demand, ENERGY STAR suggests pre-cooling your home in the morning or evening hours and shifting heat-generating chores like laundry and dishwashing to off-peak times, which reduces the load your household adds to a strained grid on the hottest days and may lower the odds of a brownout affecting your block in the first place.

Sources

Power Outages | Ready.gov, accessed 8/12/2026
Use Generators Safely at Home | FEMA.gov, accessed 8/12/2026
How To Save Electricity During Peak Demand Conditions | ENERGY STAR, accessed 8/12/2026