You lower the thermostat and nothing happens. No click, no fan, no hum from outside. A system that will not start at all is usually an electrical or control problem — which means the checks are simple, and the rule is strict: do not open anything.
Work through the safe steps below. If none of them bring the system to life, it is a service call.
Safe Checks, In Order
Do these in sequence — each one rules something out:
- Thermostat — COOL mode, setpoint below room temp. If the display is blank, the thermostat may have lost power.
- Breaker — find the AC breakers in the panel. If one tripped, reset it ONCE. If it trips again, stop and call us.
- Outdoor disconnect — the gray box near the outdoor unit has a pull-out or switch. Make sure it is in the ON position.
- Float switch — if the condensate drain clogged, a safety switch may have shut the system down. Look for water in the drain pan.
- Thermostat batteries — if it takes them, fresh batteries rule out the simplest cause.
What It Usually Is
When the safe checks do not fix it, the cause is one of these:
- Tripped float switch from a clogged condensate drain — algae shuts the system down to prevent water damage.
- Failed capacitor or contactor — power cannot reach the compressor.
- Blown fuse in the disconnect or air handler.
- Failed thermostat or control board.
- A breaker that trips the instant the system tries to start — which can be electrical or a failing AC component.
The Breaker Keeps Tripping — Now What
A breaker that trips the moment the AC tries to start is the classic two-trade symptom. It can be a failing AC capacitor pulling excessive current at startup, or a worn breaker that can no longer handle the inrush.
Reset it once. If it trips again, leave it off — forcing it risks damage to the equipment and the wiring. Because we do both trades, one visit sorts out which side is at fault. Our breaker-tripping guide covers the electrical angle.
After a Storm
If the system quit after a thunderstorm, a surge may have taken out the control board, the capacitor, or the thermostat. Do not assume it will come back on its own — surges damage components silently.
We see this after every major storm cell that rolls through. A diagnostic visit finds what the surge broke, and whole-home surge protection prevents the next one from doing it again.
Common questions
Nothing happens when I turn the thermostat down. Is the system dead?
Not necessarily. A tripped float switch, a failed capacitor, or a tripped breaker all present as a completely dead system. The safe checks above rule out the simple causes.
The thermostat display is blank. What does that mean?
The thermostat lost power — dead batteries, a tripped breaker, or a blown fuse in the air handler. Start with batteries and the breaker.
Can I open the outdoor unit to look inside?
No. There is high-voltage equipment in there, including capacitors that hold a charge with the power off. Leave the panels on and call us.
Related help
Ready when you are.
For fastest service, call now. Prefer to book online? Send a request and we'll call you back to schedule.
(561) 786-1337