Power Outage in a Phoenix Summer: What to Do With Your HVAC

Why the restart matters

When a compressor stops, refrigerant pressure between the high and low sides takes a few minutes to equalize. Attempting to start against unequal pressure means the compressor has to overcome a large mechanical load at the worst possible moment, drawing high current and stressing the motor.

Modern systems have built-in short-cycle protection — typically a three to five minute delay — that handles this automatically. Older systems often do not.

Either way, the safest practice during an outage is to switch the thermostat off. When power returns, wait five to ten minutes, then switch it back on. That single habit prevents a category of compressor stress that is entirely avoidable.

The other reason to shut it off

Power restoration frequently involves voltage irregularities — a brief surge, or a brownout as the grid comes back under heavy load. Equipment that is off during that moment is not exposed to it.

This is also the argument for surge protection in a monsoon climate. A whole-home surge protector at the panel plus a device at the HVAC disconnect costs a fraction of a control board, and monsoon season produces exactly the conditions these devices exist for.

Keeping the house livable

• Close every blind, curtain, and shade before the house starts heating
• Keep exterior doors closed; every opening lets conditioned air out and hot air in
• Close off unused rooms and concentrate in the coolest part of the house, usually a north-facing interior room on the ground floor
• Do not open the refrigerator unnecessarily — it holds temperature for hours if left alone
• Drink water continuously
• Battery fans, cool damp towels, and cool showers if water pressure holds
• Once outdoor temperature drops below indoor after dark, open windows and flush the house

When to leave

This is the part worth taking seriously. In a Phoenix summer, an extended outage is a heat safety situation, not an inconvenience.

A well-insulated house holds temperature for a few hours. After that it climbs steadily, and with no air movement and no dehumidification the interior becomes genuinely dangerous — particularly for adults over 65, infants, anyone with cardiovascular or respiratory conditions, anyone on medications affecting thermoregulation, and pets.

If an outage is expected to last through the afternoon and you have vulnerable household members, relocate. A relative, a hotel, a library, a mall, or a designated cooling center. The house will still be there.

Generators and HVAC

A portable generator will not run a central air conditioner. The starting current is far beyond what portable units deliver, and attempting it damages both the generator and the compressor.

What a portable generator can reasonably run: a refrigerator, fans, lights, phone charging, and in many cases a window unit or a portable air conditioner for a single room. That is a meaningful quality-of-life difference during a long outage.

Whole-home standby generators sized appropriately can run central air conditioning, and a transfer switch handles the changeover automatically. That is a significant installation and worth considering only for households where outages are a recurring, consequential problem.

The absolute rule with any generator: outdoors only, well away from windows and doors, never in a garage even with the door open. Generator exhaust kills people every year, and carbon monoxide is odorless.

After power returns

• Wait five to ten minutes before switching the thermostat back on
• Set it to your normal temperature rather than something much lower — the system recovers at the rate it recovers
• Listen to the startup. Anything unusual is worth investigating before running it all afternoon
• Check the breaker and outdoor disconnect if the system does not start
• If the outdoor unit took standing water during a storm, do not restore power — call for inspection first
• Reset any thermostat schedule that may have been lost