AC won't turn on
Nothing happens when you lower the thermostat? Before you call, a few safe checks can find the cause, and sometimes fix it.
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When an AC won't start at all, the cause is usually upstream of the equipment: power, the thermostat, or a safety switch doing its job. In Florida the most common safety switch is the condensate float switch, which shuts the system off when the drain backs up to keep water out of your ceiling.
What you might notice
- Thermostat screen is blank
- Thermostat calls for cooling but nothing runs
- The indoor fan runs but the outdoor unit doesn't
- The system started clicking or humming, then stopped
- Water in the drain pan under the air handler
Common causes
Thermostat power
Dead batteries or a lost 24-volt supply from the air handler leave the thermostat blank.
Tripped float switch
A clogged condensate drain trips the float switch, which cuts power to the system on purpose.
Tripped breaker or blown fuse
Often a symptom of a failing part, not the problem itself.
Failed control components
Transformers, control boards, contactors and capacitors.
Air handler door switch
If the panel isn't seated, a safety switch keeps the system off.
Safe checks you can make first
- Replace thermostat batteries if it uses them
- Confirm the thermostat is on Cool and below room temperature
- Check the AC and air handler breakers; reset a tripped one once only
- Check the drain pan and the float switch on the drain line for standing water
- Make sure the air handler access panel is closed
How a Uniform technician diagnoses it
We confirm power at each stage, from the breaker to the air handler, transformer, thermostat and outdoor unit. If a float switch has tripped, we clear and flush the drain and find out why it clogged. If a breaker tripped, we find the component drawing too much current rather than just resetting it.
Repair options
| Option | When it fits |
|---|---|
| Clear the drain and reset the float switch | The condensate line is clogged. |
| Replace thermostat or transformer | No control power reaches the thermostat. |
| Replace capacitor or contactor | The outdoor unit doesn't respond to a call for cooling. |
| Electrical repair | Damaged wiring, connections or a failing compressor drawing too much current. |
You get a written estimate after diagnosis and before any work starts. See what changes a quote in our Naples AC repair cost guide.
Why homeowners choose Uniform
The technician who comes to your home has passed a guaranteed background check and works for a licensed, insured air conditioning contractor. Florida license number posted at launch. Verify any Florida A/C contractor at DBPR.
Request a call back
Tell us what's happening and we'll call you to schedule. Every visit starts with diagnosis and a written estimate.
Other AC problems: ac not cooling, ac leaking water, frozen ac coil, weak airflow, ac runs constantly, thermostat problems, ac noise or smell, high ac electric bill, heat pump problems.
Frequently asked questions
Why is my thermostat blank?
Dead batteries, a tripped breaker, a blown control fuse or a tripped float switch are the usual causes.
How many times can I reset the breaker?
Once. If it trips again, something is drawing too much current and needs a technician.
What is a float switch?
A small safety switch on the drain line or pan that shuts the AC off when water backs up, to protect your ceiling and floors.
Need an HVAC tech you can trust in your home?
Call now. We'll ask a few questions, give you an honest arrival window and send a background-checked, licensed technician in uniform.
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