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The power went off. Then it came back, and nothing did.
Planned shutoffs during a wind event are a fact of life on this side of the county now. Most of what goes wrong around one is predictable, and about half of it can be dealt with without a contractor at all.
A restart is a sequence, and a hard restart is where the damage happens
When power returns, heating and cooling equipment does not simply switch back on. Most of it waits — a compressor has a built-in delay of several minutes to protect itself, a furnace runs through an ignition sequence, a thermostat may need to re-establish a connection before it calls for anything. Give a system fifteen minutes before deciding it has failed. A great many post-outage callouts are a system that was about to start on its own.
What genuinely damages equipment is not the outage. It is the restoration: voltage that dips, surges or cycles as the utility brings a circuit back. Control boards, capacitors and variable-speed drives are the parts that fail, and they fail at the moment the lights come on rather than during the dark.
So the two useful questions are: what exactly happened, and what backup do you already have? Both below.
What happened, and what you are working with
Nothing is sent anywhere and nothing is recorded. This is what we would ask you on the telephone.
Carbon monoxide. A portable generator produces it in quantities that are lethal indoors, and a garage with the door open is indoors. So is a carport, an alcove, a porch, and anywhere within reach of a window, a door or a vent. Run it well clear of the building and pointed away from it, and fit a working carbon monoxide alarm in the house before you ever start one. People die doing this every single year, and they are not careless people — they are people who thought an open garage door was enough.
Back-feeding. Powering a house by plugging a generator into an outlet is illegal, and it energises the utility line outside your property. That can kill a lineworker restoring power in your street, and it can kill you when the supply returns. The only correct way to connect a generator to a house is a transfer switch or an interlock, installed by a licensed electrician. We are not electricians, we do not do that work, and we will not connect one for you.
And the disappointing part. A typical portable generator cannot start a central air conditioner. The starting current of a compressor is several times its running current, and that surge is what most portables cannot supply — so the machine trips, or worse, runs on low voltage, which is how compressors are destroyed. A furnace blower or a small ductless system is a different matter and is often within reach. If you want the figures for your own equipment, they are on the nameplate, and we will read them with you rather than guess.
Wait fifteen minutes, then check three things before you call anybody
Compressors hold themselves off for several minutes after power returns. Thermostats on a network may need longer. A great many post-outage callouts are a system that was going to start on its own.
Then, in order: check the breakers, including the outdoor disconnect beside the condensing unit, which is the one people forget; check that the furnace or air handler switch — it looks like a light switch, usually beside the unit — is still on; and check the thermostat has power and is calling. If it is a battery-powered thermostat, change the batteries, because a marginal set often fails exactly when the system next tries to start.
If all three are fine and it still will not run, it is a real fault and worth a visit. Tell us what you found when you call — it saves us both time, and it occasionally saves you the visit entirely.
Find out what failed before anybody talks about replacing the system
Surge damage is usually one component rather than a machine. The control board is the most common casualty, then capacitors, then contactors, and on newer equipment the variable-speed drive. All of those are parts, and a system that lost a board is not a system that needs replacing.
What we would check: the board for visible damage — it is often obvious — capacitor values against their ratings, the contactor, and the supply voltage now that it has settled. Low or unbalanced voltage that has not recovered is a utility problem rather than yours, and it is worth establishing before fitting new parts into it.
Worth knowing about surge protection: it is an electrician’s work rather than ours, both at the panel and at individual equipment. What we can tell you is which of your units are worth protecting, which is generally the newest and most electronic ones rather than the oldest.
Start from the nameplate, not from the generator’s advertised output
The number that matters is starting current, not running current, and for a compressor the two are very different. That figure is on the equipment nameplate. Compare it with what the generator can actually supply on a surge, not with its headline rating, and you will know the answer in a few minutes.
What is usually achievable: a furnace blower, a ductless head or a small heat pump. What usually is not: a central air conditioning compressor on a portable unit. Running a compressor on a supply that cannot hold voltage is one of the reliable ways to destroy one.
Where it is worth designing for: if backup cooling or heating genuinely matters to you, say so before you replace equipment rather than after. A variable-capacity or ductless system draws very differently from a single-stage central one, and choosing with that in mind costs nothing extra at the time and is expensive to retrofit.
What we will not do: connect a generator, size an electrical supply, or fit a transfer switch. That is an electrician’s trade and we will say so rather than improvise.
Four things, none of which is equipment
Write down the restart sequence for your own system. Which breakers, which switch, where the outdoor disconnect is, and how long to wait. Stick it inside a cupboard door. It turns a stressful hour into a two-minute job that anybody in the house can do.
Cool or heat the house before the shutoff starts. Announced shutoffs usually come with notice. A house brought to temperature and then closed up will hold it for hours, and that is free.
Get the maintenance done before the wind season rather than after it. A clean coil, a correct charge and a sound capacitor are what let a system survive a hard restart. A marginal capacitor is the part that fails on restoration, and it is a cheap thing to have found in advance.
Decide what actually matters to you — keeping one room comfortable, keeping a person comfortable, keeping a business trading — because the honest answer is often smaller and cheaper than a whole-house solution, and it is a different conversation from the one a generator salesperson will have with you.
Separate the thermostat from the system, because they fail differently
A connected thermostat has two jobs: controlling the equipment and talking to a network. Those fail independently, and a great many post-outage complaints are the second one — the schedule is intact, the heating works, but the application cannot see it because the router came back with a different address or the device is waiting to re-join.
Try this first: operate the thermostat at the wall rather than through the application. If the system responds, you have a network problem rather than a heating problem, and the person to call is whoever looks after your network.
Two genuine faults worth knowing about: thermostats powered from the system’s own low-voltage supply lose their settings if that supply is interrupted and there is no battery backing them, and some models need a full power cycle at the equipment rather than at the wall to re-establish communication.
And a plain opinion: in an area with regular planned shutoffs, a thermostat that keeps a usable schedule without a network connection is worth more than one with more features. We will say which of the ones we fit do that.
About a system that did not restart
Find your outdoor disconnect now, while nothing is wrong, and photograph it. It is a small grey box beside the condensing unit, and it is the single most commonly missed item on this list.
About suspected surge damage
Ask for the failed part to be shown to you and for the replacement to be priced on its own. A board failure is a repair, and it should be quoted as one before any conversation about a system.
About generators
Get the starting current off your own equipment nameplate before you buy anything. It is printed there, it takes a minute, and it is the number every honest answer depends on.
About preparing
Book the service before the wind season rather than after it. The capacitor that fails on restoration is the one that was already marginal in September.
About thermostats
Operate it at the wall before you conclude the heating has failed. It separates a network problem from an equipment problem in ten seconds and saves a visit surprisingly often.
With no backup at all
Which is a perfectly sensible position for most households. The cheap preparation on this page — the written restart sequence, pre-cooling before an announced shutoff, and maintenance done before the season — covers most of what backup would buy you, for almost nothing. Decide what genuinely matters to you before anybody sells you a solution to it.
With a portable generator
Read the note above before anything else on this page. In short: carbon monoxide kills people who thought an open garage door was enough; back-feeding through an outlet is illegal and can kill a lineworker; and a typical portable will not start a central compressor. None of those are opinions.
With a standby generator
Then the constraint is what it was sized for, which was decided when it was installed and may not include air conditioning. Find the load schedule from that installation, and if you are replacing heating or cooling equipment, tell us what the generator can carry before we choose anything — equipment with a soft start or variable capacity draws very differently from a single-stage machine.
With a home battery
Batteries are limited by how much they can deliver at once as well as by how long they last, and a compressor start is a demanding moment for both. Your installer can tell you what the system will support; ask them rather than us, and tell us the answer before equipment is chosen. A ductless or variable-capacity system is generally far easier on a battery than a single-stage central one.
The four things to have written down before the next one
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Where your breakers and disconnects are
Including the outdoor disconnect beside the condensing unit. Photograph them, and put the photographs somewhere that does not need the internet to open.
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How long to wait before deciding it has failed
Fifteen minutes, as a rule. Written on the same sheet, so nobody in the house calls anyone in the first five.
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What your equipment actually draws on starting
Off the nameplate. It settles every generator and battery question before any money is spent.
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Who to call for what
An electrician for transfer switches, surge protection and supply. Us for the equipment. Nobody at all for the first fifteen minutes.