AirConditionAnswers

AC Troubleshooting: What's Wrong With Your Air Conditioner?

Pick the symptom. Each page starts with the free checks that fix a surprising number of problems, then the likely causes, what each repair typically costs, and how to tell a fair quote from an inflated one.

By ·Updated

Not cooling

It runs, but the air isn't cold or the house won't cool down.

AC blowing warm air

The fan runs but the air coming out of the vents is warm or barely cool.

Won't run

Nothing happens, or part of the system stays off.

AC won't turn on

Nothing happens when you lower the thermostat: no fan, no outdoor unit.

Outdoor unit not running

The indoor fan blows but the outside unit is silent, humming or its fan is still.

AC not working after a power outage

Power is back on, but the AC won't start or doesn't cool.

Water and ice

Leaks, a full drain pan, or ice on the coil or lines.

AC frozen up

Ice on the copper lines or indoor coil, weak airflow, water as it melts.

AC leaking water

Water around the indoor unit, a dripping ceiling or a full drain pan.

Start here: three checks that fix most problems

  • The thermostat. Mode on Cool, fan on Auto, set a few degrees below the room, fresh batteries, no schedule overriding it. Then wait 5–10 minutes: many systems delay restarting.
  • The air filter. A clogged filter causes weak airflow, poor cooling, frozen coils and higher bills. Replace it if you can't see light through it.
  • The breakers. There are usually two: one for the indoor unit and one for the outdoor unit, plus a disconnect box beside the outdoor unit. Reset a tripped breaker once only.

Stay safe. Switch off power at the breaker and the outdoor disconnect before opening any panel. Never touch the capacitor; it holds a charge even with the power off. Refrigerant work needs a licensed technician. If a breaker trips twice, or you smell burning, turn the system off and call.

Why these pages exist

I'm not an HVAC contractor. I'm the one paying the invoices, for several stores where the air conditioning runs most of the year. I've learned to handle the routine fixes myself and to recognize when a quote doesn't match the problem. A lot of service calls come down to a cheap part or a clogged drain, and a "you need a new system" verdict sometimes turns out to be a capacitor. These pages are the checks I'd do before picking up the phone, and what I'd want to know before agreeing to a price.

Before you agree to a repair

  • Expect a service call fee of about $75–$200. It's often credited toward the repair if you go ahead.
  • Ask what failed and why, and ask to see the old part.
  • Refrigerant doesn't get used up. If it's low, ask where the leak is before paying for a recharge.
  • For a big repair on an older system, compare it with replacement using the repair vs replace calculator.
  • Check typical prices in AC repair costs in 2026.

More problems are on the way: noises, smells, short cycling, high humidity and mini-split error codes.

Stop Overpaying for Heating & Cooling.

The most expensive HVAC repair is the one that catches you off guard in July. Get our free HVAC Maintenance & Savings Checklist — seasonal checklists for central AC, furnaces, and ductless mini-splits, a complete filter selection guide, and the 5 questions to ask your technician before agreeing to any repair or replacement.

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