HVAC Troubleshooting

Power's Back But HVAC Won't Start?

After a Houston storm or power outage, your HVAC system may need a manual reset. Here's the step-by-step.

What's Going On

Understanding the Problem

The power went out (storm, grid issue, rolling blackout) and when it came back on, everything in the house works except the HVAC system. The lights are on, the fridge is running, but the AC or heater won't respond. This is one of the most common calls we get after Houston thunderstorms and tropical weather events.

Diagnosis

Common Causes

1Compressor time delay

AC systems have a built-in 5–10 minute time delay that prevents the compressor from restarting too quickly after a power interruption. This protects the compressor from damage. The system seems dead, but it's actually just waiting.

2Tripped breaker

Power surges when electricity is restored can trip breakers. Your HVAC system may have two breakers (indoor and outdoor) — both need to be on.

3Thermostat reset

Some thermostats lose their programming during an outage. They may come back in an off state, a default mode, or with the schedule cleared. Battery-backed thermostats hold settings through outages.

4Blown fuse in disconnect box

The power surge that accompanies restoration can blow the fuses in the outdoor disconnect box. Power reaches the breaker panel but not the outdoor unit.

5Surge damage to control board

In severe cases, a power surge can damage the HVAC system's control board, capacitor, or compressor. If the system was running when power dropped and surged back, sensitive electronics can be fried.

DIY Troubleshooting

What You Can Try

Wait 15–30 minutes

Seriously — just wait. The compressor time delay, thermostat reboot, and system self-checks all take time. Most post-outage HVAC calls resolve on their own within 30 minutes of power restoration.

Check and reset both breakers

Go to the electrical panel. Turn off both HVAC breakers (indoor and outdoor), wait 30 seconds, then turn them back on. Give the system another 5 minutes after resetting.

Check the thermostat

Make sure it powered back on and is set correctly. Reset the mode (COOL or HEAT), set the desired temperature, and check that the fan is on AUTO. If the screen is blank, replace batteries.

Check the outdoor disconnect

The disconnect box near the outdoor unit has fuses that can blow during surges. If the indoor fan works but the outdoor unit is dead, blown fuses in the disconnect are likely.

Reset at the unit

Some outdoor units have a reset button on the unit itself (usually a small red or yellow button near the refrigerant lines). Press it once and wait 5 minutes.

Know When to Call

When to Call a Pro

If the system doesn't respond within 30 minutes of power restoration and breaker resets, it may have surge damage. If the breaker trips again immediately after resetting, stop — there's an electrical problem. If you hear unusual sounds (clicking, buzzing without the fan running), the capacitor or contactor may be damaged. Call for a post-storm assessment.

Call (713) 478-5655 Schedule Online

Pro Tip

Invest in a whole-home surge protector (installed at the electrical panel, $150–300 installed) to protect your HVAC system and electronics from power surge damage. Houston's frequent thunderstorms and occasional grid instability make surge protection a smart investment. Some HVAC manufacturers void warranty claims for surge damage if no surge protector was installed.

Need a Pro?

Services That Solve This

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