When an AC won’t turn on at all, the problem is almost always power or a safety cutoff — not a dead system. A blank thermostat, a tripped breaker, a full condensate pan, or a bumped emergency switch can each shut everything down. Walk through this checklist in order and you’ll restore power in most cases. If the system still won’t start after all of it, the fault is internal and needs a tech.
Watch how it's done
Video: Fix This House. Shown for reference — not affiliated with GetHoustonLeads.
What you'll need
- Fresh AA/AAA batteries
- A flashlight
- A wet/dry vacuum
Recommended parts & supplies
- Thermostat batteries — a dead thermostat is the #1 easy fix
- Smart / programmable thermostat — upgrade if yours keeps failing
- Wet/dry shop vacuum — clears the condensate drain clog
- Multimeter — checking a live disconnect is 240V work — leave it to a pro unless you are qualified
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Step by step
- 1
Check the thermostat screen and batteries
A blank or frozen thermostat can’t call for cooling. Swap in fresh batteries, then set it to COOL and lower the temperature several degrees. If the screen lights up and the system starts, you’re done. Also confirm nobody set it to “hold” or a schedule that’s keeping it off.
- 2
Look for a tripped breaker in the main panel
Open your electrical panel and find the breaker(s) labeled for the AC or air handler. A tripped breaker sits in the middle position. Push it firmly to OFF, then back to ON. If it trips again immediately, do not keep resetting it — that’s a fault that needs a professional.
- 3
Check the furnace/air-handler switch
Your indoor air handler (often in a closet, attic, or garage) has a switch nearby that looks exactly like a regular light switch — and gets flipped off by accident all the time. Make sure it’s ON. Attic units may also have a service switch at the top of the stairs.
- 4
Reset the outdoor disconnect
Next to the outdoor condenser is a small box with a pull-out block. Make sure it’s fully seated (some pull out and flip). This is a common culprit after yard work or a prior repair.
- 5
Clear the condensate drain and check the float switch
In humid Houston, a clogged condensate drain trips a float safety switch that deliberately shuts the system off to stop water damage. Find the PVC drain line and the small pan under the indoor unit. If the pan has water, clear the drain line with a wet/dry vacuum on the outdoor end until it sucks the clog free, then empty the pan. Many “dead” systems roar back to life the moment the float drops.
- 6
Wait five minutes for the built-in delay
Modern systems have a short-cycle protection delay — after power is restored they wait a few minutes before starting, to protect the compressor. Restore everything, then give it a full five minutes before deciding it’s still dead.
When to call a pro
If the thermostat is powered, the breaker holds, and the float switch is clear but the system still won’t start, the problem is likely a failed capacitor, contactor, control board, or blower motor — all of which involve live electrical components and belong to a licensed tech. Call immediately if a breaker trips repeatedly, you smell hot plastic, or the outdoor unit hums loudly without the fan spinning (a classic failed-capacitor sign that can burn out the motor if left running).
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AC Not Turning On At All — FAQ
Why did my AC suddenly stop working with no warning?
What is the float switch on my AC?
Why does my AC breaker keep tripping?
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