- Home
- Power cuts
The power going off is rarely the problem. What happens either side of it usually is.
On this part of the Gulf coast the grid is a design condition, not an accident. Most of the equipment damage we see around an outage happens in the minutes before it and the minutes after it — and almost all of it is preventable for a fraction of what the repair costs.
If it tripped or shut down when the power returned and it will not restart, do not keep cycling the breaker or the thermostat. Each attempt puts a compressor or a motor through another start against whatever is actually wrong, and repeated attempts are the most reliable way to turn a small fault into a large one. Switch the system off at the thermostat, leave it off, and ring somebody. If anything smells hot, anything is discoloured, or a breaker trips a second time, stop there and call — a breaker that trips twice is a message, not a nuisance.
Voltage sagging under load
A brownout is not a small power cut — in some ways it is worse. Motors are designed for a voltage range, and below it they draw more current to do the same work and get hotter doing it. A compressor asked to start on low voltage is the classic way to damage one, because the start is when it is drawing the most and the voltage is at its lowest.
The frustrating part is that it leaves no obvious mark. Nothing trips, nothing bangs. It shortens the life of the most expensive component in the system quietly, over several summers, and the failure eventually gets blamed on age.
The power is off right now
The system is doing nothing, which is safe. What matters is what happens in the next few minutes and what happens when the supply returns — because supplies frequently come back unstable, flicker, and go off again.
The single most useful thing you can do is switch the cooling off at the thermostat so the system does not attempt to start the instant the power returns, and leave it off for a few minutes after it does. Everything else on this page is about preparation; this is the one thing that helps while it is happening.
It came back and the system will not start
Four ordinary causes, in the order we find them. A tripped breaker or blown fuse in the outdoor disconnect. A capacitor that failed trying to start against a sagging supply. A contactor welded or pitted by the switching. Or a control board or transformer that took the surge.
There is also a fifth that is not a fault at all: many systems have a built-in delay of several minutes before the compressor will restart, deliberately, to protect it. If it has been less than that, it may simply be waiting.
Rolling outages expected
The most controllable version of this, because you have notice. Repeated short outages are harder on equipment than one long one, since each restoration is another start attempt against a supply that may still be unstable.
The useful preparation is not dramatic: decide in advance that the cooling goes off at the thermostat when the power does, and stays off for a few minutes after it returns. A system that is switched off at the thermostat cannot attempt a start into an unstable supply, and that single habit prevents most of what we get called to afterwards.
Thinking about a generator
Worth doing properly and worth understanding first, because the gap between what people expect and what a generator delivers is wider here than anywhere else in this trade.
The honest headline: a portable generator will usually not run central air conditioning. The running load is one thing; the starting surge of a compressor is several times that, and it is the surge that decides. Portable units generally cover lighting, a refrigerator, fans and phone charging — which is genuinely worth having, and is not cooling.
And the safety part is not optional. A generator is never run indoors, in a garage, or anywhere its exhaust can reach a building — carbon monoxide from generators kills people every storm season. Connecting one to a building’s wiring requires a properly installed transfer switch and a licensed electrician; back-feeding through an outlet is illegal, and it can kill a lineworker.
Central air with a gas furnace
The vulnerable part is the outdoor unit, and specifically the compressor, the capacitor and the contactor — the three things that take the strain of a start. The furnace itself is electrically light, but it will not run at all without power, because the blower, the igniter and the control board all need it.
Worth knowing: your gas furnace is not a power-cut heating solution. It needs electricity even though the heat comes from gas, and in a Gulf coast winter that matters less than it would further north — but it still means no heat in a hard freeze, which is exactly when the grid is under most strain.
A heat pump
Everything that applies to a central system applies here, with one addition: a heat pump is your heating as well as your cooling, so an outage or a damaged compressor takes both.
The other thing to watch is what happens afterwards. If a heat pump comes back and runs on auxiliary electric heat because something in the outdoor unit or its controls did not survive, the house will stay warm and the bill will be extraordinary — and nothing will alert you. After any significant electrical event it is worth confirming the heat pump itself is actually running rather than the strip heat.
Window units or mini-splits
Individually less exposed, because each machine is smaller and the starting surges are smaller — but there are more of them, and on window units the weak point is frequently the outlet and the cord rather than the machine.
Never on an extension lead or a power strip. Most are not rated for the current a compressor draws on start-up, and a warm plug or a warm outlet after an electrical event means stop using it and get an electrician.
A mini-split has its own outdoor unit and its own board, and is as exposed to surge as any other system. On the useful side, a single mini-split zone is within reach of a larger generator in a way that central air generally is not — which is worth knowing when planning.
What actually helps with low voltage
- Switch the cooling off during the event. A system that is not calling cannot attempt a start on a sagging supply.
- Have the voltage and the start current measured under real conditions rather than assumed. It is a short visit and it produces numbers.
- A hard-start kit gets a struggling compressor over its start faster and can genuinely help on a marginal supply — but it is a remedy for a specific measured problem, not something every system should have. If somebody offers one without measuring, ask what they measured.
- Surge protection at the equipment, and ideally at the panel by an electrician, is inexpensive next to a control board.
- If the supply itself is sagging, that is between you and the utility, and it is worth reporting. It is not something we can fix at the equipment.
What to do while it is off
- Switch the cooling off at the thermostat. The single most useful action available to you, and it costs nothing.
- Leave it off for several minutes after the power returns, and longer if the supply is flickering. Let the grid settle before asking a compressor to start into it.
- Keep the house closed and the blinds drawn on the sunny side. A well-closed house holds temperature for hours, and it is the only cooling you have.
- If it is hot and the outage is long, treat that as a health question rather than an equipment one — cooling centres, neighbours, and anybody in the house who is vulnerable to heat come first.
- Do not run a generator indoors or in a garage, ever, whatever the weather is doing.
What to check, and what not to touch
- Wait out the built-in delay first. Several minutes on most systems. It may simply be protecting itself.
- Check the thermostat — some lose their programme or their clock after an outage and come back on a default that is not what you want.
- Look at the panel for anything tripped. Reset once. If it trips again, stop.
- Do not open the outdoor unit. A capacitor holds a charge after the power is off, which is precisely why this is not a home repair.
- Anything hot, discoloured or smelling — switch it off at the breaker and ring. That is not a wait-and-see.
- On a heat pump, check whether it is running on strip heat. The house being warm proves nothing about whether the heat pump survived.
What to set up before the week starts
- Agree the habit: cooling off at the thermostat when the power goes, on again a few minutes after it is back and steady. Tell everybody in the building, because it only works if it is done every time.
- Pre-cool the building before a scheduled outage rather than trying to catch up afterwards. A cool building coasts; a warm one never recovers.
- Have surge protection fitted now rather than after. It is cheap against a control board and cheaper still against a compressor.
- Change the filter. Trivial, and it means the system is not also fighting a restriction on the day it is asked to recover a hot building.
- If you run a business, decide in advance what happens to stock, to a server cupboard and to anything refrigerated — those decisions are worse made at short notice.
What to establish before you buy anything
- What you actually want to run, written down, and whether cooling is genuinely on that list. If it is, you are in standby-generator territory, not portable.
- The starting surge, not the running load. A compressor’s start is several times its running current, and that number is what sizes the generator. A soft-start device can reduce it materially and is sometimes the difference between a workable plan and an unworkable one.
- A transfer switch and a licensed electrician. Non-negotiable, and not our trade — we will work alongside an electrician and we will not wire a generator to a building.
- Where it goes and where the exhaust goes. Never indoors, never in a garage, never where exhaust can reach a window, a door or an intake.
- What it costs to keep, not just to buy — fuel, exercise runs and servicing. A standby generator that has not been run in two years is a decoration.
- Consider zoning your expectations. Cooling one room reliably is frequently more achievable than cooling a whole house, and a mini-split makes that a real option.
Three things worth doing before storm season
Surge protection
At the equipment and, better, at the panel by an electrician. Inexpensive against a control board and trivial against a compressor.
Measured voltage and start current
Under real conditions, written down. It tells you whether a hard-start kit is a remedy or a sale, and it gives you a baseline.
A raised, secured outdoor unit
On this coast, off the ground and properly strapped. It is a flooding and a wind question as much as an airflow one.