How to Protect Your Air Conditioner from Power Surges, Brownouts and Outages

I run several retail stores in the Caribbean. On an island grid, outages, flickers and brownouts aren't emergencies; they're part of a normal week, and a dead AC in a store means lost customers that afternoon. Here's what we actually do:

• Delayed starts on the condensers. When power comes back, our units don't all start at the same moment. Each waits its turn, so the compressors aren't fighting each other, or a weak grid, for starting current.
• Everything off before a hurricane. Before a storm, every unit is switched off and its breaker is turned off, so a surge or lightning strike on the line has nothing running to damage.
• Voltage protection on refrigeration. We've lost refrigerators and their compressors to brownouts, so that equipment now runs through appliance protectors that watch the voltage: when it drops, they cut power, and they wait a few minutes before reconnecting.

The most important point below is one that's easy to miss: surges and brownouts are different problems, and the device that stops one doesn't stop the other.

The four ways bad power damages an AC

Surge protector vs. voltage protector: not the same thing

A surge protector clamps voltage spikes that last a few millionths of a second. It's what you want against lightning nearby or the jolt when the utility switches lines. It's mostly the electronics (control boards, thermostats, the inverter in a variable-speed system) that die from surges.

A brownout is the opposite: voltage that stays too low. A motor that's asked to do the same work on less voltage draws more current, and more current means heat. One HVAC company cites winding temperatures rising 10–15% for every 10% drop in voltage. Run a compressor like that for an afternoon, or start and stop it repeatedly on a sagging line, and the windings burn out. That's the expensive part: a compressor replacement typically runs $1,500–$3,000, often enough to make replacing the whole system the better deal.

A surge protector does nothing about low voltage. What does is a voltage monitor (sold as compressor protectors, voltage protectors or brownout protectors): it watches the supply and disconnects the unit when voltage goes too low or too high, then waits until power has been normal for a few minutes before reconnecting. Many models include surge protection too, so one device at the outdoor unit covers both problems and adds a restart delay.

Delay timers: the cheapest protection there is

When an AC stops, the refrigerant is at high pressure on one side of the compressor and low on the other. It takes a few minutes to even out. If power drops and returns in seconds, the compressor tries to restart against that pressure difference, can stall, and draws locked-rotor current until its overload trips. Do that a few times during a flickering outage and it adds up.

A delay-on-make timer holds the unit off for a set time (typically 3–5 minutes) after power returns. Set different delays on different units and they come back one after another instead of all at once, which is easier on the grid, on your building's wiring and, if you're on one, on your generator. Many thermostats and newer outdoor units already have a short delay built in, so check before adding one; for older equipment it's a small part and a quick job for a technician.

Hard-start kits and soft starters

These are often confused. A hard-start kit (an extra capacitor and relay) gives the compressor a stronger kick to get going. It helps an aging compressor or one on weak voltage start, but it treats a symptom: if a technician recommends one, ask why the compressor is struggling.

A soft starter does the reverse: it ramps the compressor up gently, cutting the surge of current it pulls at start-up. Emerson says its SecureStart module reduces starting current by up to 75%. That means less light flicker, less strain on a weak supply, and, most usefully, the ability to run an AC from a smaller generator than it would otherwise need.

What each device costs

Approximate U.S. prices. Installation labor varies by location; in the Caribbean, expect parts to cost more and to take longer to arrive, so stock spares.

Set those against what they protect: a control board or contactor is a few hundred dollars to replace, a compressor $1,500–$3,000, and a whole system $5,000–$15,000. If your grid has regular brownouts, a $200 voltage protector on each outdoor unit is one of the best-value purchases you can make for your cooling.

What to protect first

1. Frequent brownouts or flickering power: a voltage monitor with surge protection and restart delay at each outdoor unit.
2. Several units on one building: staggered delay timers so they don't restart together.
3. Lightning-prone area, or a new or upgraded electrical service: a whole-house surge protector at the panel.
4. Variable-speed (inverter) system: surge protection matters more, because there's more electronics to lose. See 16 vs 18 SEER for the trade-offs of these systems.
5. Long outages and a generator: a soft starter, so the generator can actually start the AC.

Running AC on a generator

The common mistake is sizing a generator for the AC's running draw. A compressor's starting current, listed as LRA (locked-rotor amps) on the outdoor unit's nameplate, is several times higher than its running current, and the generator has to supply it for that first second or the unit won't start. Ask the installer to size the generator from the LRA of everything that will start on it, or add a soft starter to bring that number down.

• Use a transfer switch or interlock installed by a licensed electrician. Plugging a generator into the building's wiring without one can send power back onto the utility line, which can kill a line worker, and can wreck the generator when grid power returns.
• Run it outdoors, at least 20 feet from doors, windows and vents, and keep a battery-powered carbon monoxide alarm inside, as the CDC advises. Never in a garage, even with the door open.
• Start loads one at a time, the largest first, and let each settle before starting the next.

Hurricane checklist for your AC

Before the storm

• Turn every unit off at the thermostat, then turn off its breaker or outdoor disconnect. This is what we do at every store.
• Clear loose items around the outdoor units: furniture, planters, branches, anything that can become a projectile.
• Check the condenser's tie-down straps or anchors. In hurricane zones, building codes often require them.
• Take photos of each unit and its nameplate for insurance.
• Don't wrap a running unit in a tarp; if you cover it, only once it's off, and remove the cover before restarting.

After the storm

• Wait until the grid has been stable for a while. Power often comes back and drops again several times.
• Walk around each outdoor unit: debris inside, bent fins, a shifted pad, damaged wiring or refrigerant lines.
• If the unit sat in floodwater, don't turn it on. Have a technician inspect the electrical components first.
• Turn breakers back on, then start units one at a time from the thermostat. Listen for grinding, buzzing or a unit that won't start.
• Check that the condensate drain is clear; storm debris and algae can block it and flood the indoor unit.

Frequently asked questions

Sources

• Generator safety: CDC, Prevent Carbon Monoxide Poisoning.
• Soft-starter current reduction: Emerson (Copeland) SecureStart (manufacturer figure).
• Whole-house surge protector costs and NEC 230.67: AJ Long Electric cost guide (2026).
• Low voltage and motor heating: Charles & Hudson.
• Repair costs: our AC repair cost guide. Device part prices are typical U.S. retail ranges.
• Electrical work on HVAC equipment and generators should be done by a licensed electrician or HVAC technician.