The power came back and the AC did not.
Some of this is the system protecting itself. Some of it is real damage from the way the power came back.
Monsoon season takes the power out, and a fair number of AC calls in August start with “it was fine until the lights flickered.”
Most of these are not damage. Some are.
Wait ten minutes first
Most systems have an anti-short-cycle delay, commonly around five minutes, which stops the compressor restarting against high head pressure. After an outage that delay runs, and during it the thermostat may be calling while nothing outside happens.
A system that comes back on its own at minute six is working correctly. A lot of service calls get cancelled by waiting.
Then check, in this order
The thermostat. Many lose their settings or their schedule after a power loss, and some lose programming entirely. Confirm it is on COOL, the setpoint is below room temperature, and the fan is on AUTO. Battery backed thermostats with tired batteries often will not come back at all.
The breaker. Restoration surges trip breakers. Reset once. If it trips again, stop, and read the breaker guide.
The disconnect beside the outdoor unit.
The float switch. If the system was off for hours in summer and then came back, nothing drained during the outage, but a pan that was already marginal can tip over. A dead system with no other symptom is very often this.
Outside. Fan spinning, compressor humming, or silence.
What the restoration can actually break
Power rarely returns cleanly. It often comes back as a surge, or in stages with a period of low voltage, which is called a brownout.
A motor running on low voltage draws more current to make the same torque. That is hard on everything:
The capacitor, which is the most likely casualty and the cheapest. A unit that hums without starting after an outage is the classic.
The contactor, which can weld or pit.
The control board, on systems that have one. Electronics mind surges more than motors do.
The compressor, in the worst case, from repeated attempts to start on low voltage.
If it keeps happening
Repeated outages in one season are worth mentioning when you call. A system that has been through several brownouts has usually taken some cumulative wear, and the components most likely to show it are measurable: microfarads on the capacitor, amp draws under load, and the contactor contacts.
Surge protection at the panel or at the unit is an electrician’s job rather than an HVAC one, and in a monsoon climate it is a reasonable thing to ask about.
Questions that come with this one.
How long should I wait before deciding it is broken?
Give it at least ten minutes after power is restored. Many systems have a built in delay, usually around five minutes, to stop a compressor restarting against high head pressure. A system that comes back at minute six is behaving normally.
Can an outage actually damage the AC?
The outage itself rarely. The restoration can, because power often comes back as a surge or returns in stages with low voltage in between. Motors running on low voltage draw high current, and that is hard on windings, capacitors and contactors.
Is a surge protector worth it?
For HVAC equipment in an area with frequent monsoon outages, many people think so, particularly on systems with electronic control boards or variable speed motors. It is an electrical install rather than HVAC work, so it goes to an electrician.
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