AC troubleshooting: find your symptom, then the fix

Which AC symptom matches yours?

Pick the line that sounds like your system. Each row names the searcher's symptom, its likeliest cause, and whether you're looking at a DIY check or a licensed repair — the linked ones open a full walkthrough, and the rest are covered by the universal checks below.

What should you check first, whatever the symptom?

Before diagnosing anything specific, these six checks rule out the culprits behind most AC calls — and every one is free. Work them in order; a clogged filter or a tripped float switch alone accounts for a large share of what feel like total failures. The list names each check and what it rules out:

1. Thermostat. On COOL, set 3°F below room temp, batteries fresh. A dead cell blanks the whole system.
2. Air filter. Hold it to a light — if none passes through, replace it. A clogged filter sits behind a large share of AC 'failures.'
3. Breaker + outdoor disconnect. Reset the breaker once, then check the gray disconnect box by the outdoor unit — a pulled fuse block there is the most-missed cause.
4. Condensate float. A full drain pan or clogged line trips a float switch that shuts cooling off on purpose to protect your ceiling.
5. Condenser clearance. Clear 2 ft around the outdoor unit and rinse the coil — a coil choked with cottonwood or grass can't shed heat.
6. 3-minute rule. After power returns the compressor waits up to three minutes by design. A unit that seems dead may just be counting down.

Cleared all six and it still won't cool? The remaining causes are internal — a capacitor, refrigerant, a motor, or the control board — and that's licensed-technician territory.

What are the most common AC repairs — and what do they cost?

When the free checks don't solve it, the fault is almost always one of six parts. This list is ordered by how often each actually comes up in summer, with a typical installed price range so you know the repair before the tech arrives:

Full part-by-part pricing lives on AC repair cost, and the visit fee itself on HVAC service call cost.

Why can't my AC keep up on the hottest days?

Sometimes nothing is broken at all. On a 95–100°F+ day a correctly working AC only holds a 15–20°F difference between the air it pulls in and the air it blows out — so an undersized or aging system running flat-out and still losing ground is overloaded, not faulty. The way to tell them apart is the vent split, not the room temperature:

If the split holds 15–20°F, there's no part a technician can swap to beat physics — the fix is shade, sealing, or a right-sized system, covered in AC running but not cooling and what size AC you need. A split under 15°F, though, points to low charge or a dirty coil, and that's worth a call.

Does this cover window units — and when should you call?

This guide covers central and split systems. For a window or portable unit, the fix is usually the manufacturer's reset button plus a clean filter — beyond that they're cheap enough to replace rather than repair. Once you've cleared the universal checks and matched your symptom on a central system, the internal repairs above — capacitor, refrigerant, motors, board — are licensed-technician work, because they involve sealed refrigerant circuits and high voltage. One safety line worth repeating: a capacitor holds a charge even with the power off, so opening the outdoor panel is a real shock hazard.

Frequently asked questions