AC not blowing cold air: what to check, in order, before you call a technician

Find your symptom first

Step 1: the thermostat and the remote

Start here: plenty of "broken AC" (or "broken aircon", as it is called in the UK) moments end at the thermostat or the remote.

1. 01

   Mode

   Set it to Cool. On a heat pump, Heat or Emergency Heat will blow warm air by design. On a mini-split remote, check the symbol: a snowflake for cooling, a drop for Dry, a fan for Fan only.

2. 02

   Set point

   Lower it a few degrees below the current room temperature so the thermostat actually calls for cooling.

3. 03

   Fan setting

   Choose Auto. With the fan on On, the blower keeps running between cooling cycles and pushes room-temperature air, which feels like the AC has stopped working.

4. 04

   Power

   Replace the batteries if the screen is dim or blank. A smart thermostat may show a wiring or Wi-Fi error, or a schedule that overrides your setting.

5. 05

   Wait

   Some thermostats and outdoor units have a built-in delay of a few minutes before the compressor restarts. Give it time before you change anything else.

Step 2: the air filter

A clogged filter starves the indoor coil of air. Cooling drops, the system runs longer and the coil can freeze. ENERGY STAR advises inspecting the filter once a month and cleaning or changing it as needed; University of Georgia Extension recommends replacing or cleaning it at least every three months. Pets, dust, renovation work and constant summer use all shorten that interval.

• Find the filter at the return grille or in a slot next to the indoor unit (furnace or air handler).
• Note the size printed on the frame and the airflow arrow; the arrow points toward the unit.
• Make sure the new filter fits snugly so air passes through it rather than around it.
• On a mini-split, open the front cover of the indoor head, slide out the mesh filters, rinse them, let them dry fully and refit them.

Step 3: breakers, fuses and the outdoor disconnect

A central system usually has two breakers in the main panel, one for the indoor unit and one for the outdoor unit, plus a disconnect box on the wall next to the outdoor unit.

1. 01

   Check the panel

   Look for a breaker sitting in the middle position or labeled AC, condenser, air handler or furnace. Push it fully off, then back on.

2. 02

   Check the disconnect

   Lift the cover next to the outdoor unit. It may have a pull-out block or a lever; make sure it is in the On position. Leave any fuses inside it to a technician.

3. 03

   Check the indoor unit switch

   Furnaces and air handlers often have a switch that looks like a light switch on or near the unit. It also needs to be on, and the blower door must be closed firmly, because many units have a door safety switch.

4. 04

   Reset once only

   If a breaker trips again, leave it off. Repeated tripping points to a short, a failing motor or a compressor drawing too much current, and resetting it again can damage the equipment.

If the whole house is dark, see our power outage guide instead.

Step 4: look at the outdoor unit

With the system calling for cooling, go outside. A healthy outdoor unit has its fan spinning and a steady compressor hum, and warm air comes out of the top.

• Fan still, unit humming: switch off at the disconnect and call a technician. This often points to the capacitor, a component that stores electrical energy to start the motors, or to the fan motor itself. Testing and replacing it is technician work.
• Everything silent: recheck the breaker and disconnect, then look indoors at the drain pan (Step 6).
• Coil clogged: grass clippings, cottonwood fluff, leaves and dog hair on the fins stop the unit from shedding heat. Switch off the power, clear debris by hand and rinse the fins gently with a garden hose, as University of Georgia Extension suggests. A pressure washer bends the thin fins.
• Crowded unit: trim back shrubs and move stored items, fences or covers so air can flow freely on all sides and out of the top. Remove any winter cover before the season starts.
• Dirt splash: a layer of mulch or pine straw around the unit keeps soil from splashing onto the fins in heavy rain.

Step 5: check for ice

Ice on the copper line at the outdoor unit, on the indoor coil or dripping from the air handler means air or refrigerant is out of balance. Running the system iced up only makes the block of ice bigger and puts strain on the compressor.

1. 01

   Cooling off, fan on

   Set the thermostat to Off (or Heat with the set point low enough that heating stays off) and the fan to On. Moving room air over the coil speeds the thaw.

2. 02

   Protect the floor

   Put towels around the indoor unit; a melting coil releases a lot of water and the drain pan can overflow.

3. 03

   Let it melt completely

   This can take several hours. Chipping at the ice damages the coil fins and tubing; let it thaw on its own, without a heat gun or hair dryer.

4. 04

   Fix the airflow

   Fit a new filter, open all supply vents and clear furniture away from return grilles.

5. 05

   Restart and watch

   Once everything is dry, return to Cool. If ice comes back within a day, the likely cause is low refrigerant or a blower problem, and both need a technician.

Step 6: the condensate safety switch

As your AC cools, it pulls water out of the air. That water runs into a pan under the indoor coil and away through a drain line. Many systems have a float switch in the pan or on the drain line that cuts the cooling when water backs up, to protect your ceiling or floor. Building codes accept this kind of automatic shut-off as one way to guard against an overflowing pan in attics and upper floors.

The giveaway is an indoor fan that keeps running while the outdoor unit stays off, with water standing in the pan or the drain fitting. Clear the drain and the switch usually resets by itself once the water drops. Our guide to an AC leaking water explains how to clear the line safely. Leave the switch in place: bypassing it removes the protection and the pan will simply overflow.

Low refrigerant, capacitors and other pro-only faults

Some faults are outside homeowner territory, by law or for safety.

• Refrigerant. An AC is a sealed system; refrigerant runs low only if it leaks. Under Section 608 of the Clean Air Act, EPA requires technicians who maintain, service, repair or dispose of equipment that could release refrigerant to be certified, and refrigerant for home systems is sold only to certified technicians and their employers. EPA also warns that propane-based products labeled "22a" or "R-22a" are flammable and approved for no existing air-conditioning system.
• Capacitors and contactors. These parts start and switch the compressor and fan motors on high-voltage circuits; testing them needs a meter and training.
• Compressor, fan motor and control boards. Diagnosis and replacement need specialist tools.

Keep it cooling all summer

• Check the filter monthly during the cooling season.
• Book a professional check-up each spring before the heat arrives, as ENERGY STAR recommends; it should cover refrigerant level, electrical connections, motors, the drain and the thermostat.
• Pass a stiff wire or a drain brush through the condensate drain channels about every six months (University of Georgia Extension) or use the cleaning method your manual gives.
• Keep the outdoor unit clear of plants, grass clippings and stored items.

Sources

Official guidance and extension advice, checked on 27 October 2026.

• ENERGY STAR · Maintenance checklist ↗Monthly filter checks, annual spring check-up, thermostat settings, condensate drain, refrigerant level, electrical connections and motor checks.
• University of Georgia Cooperative Extension · Maintaining your heating and cooling systems ↗Filters at least every three months, stiff wire through condensate drains every six months, hosing the outdoor fins, mulch around the unit.
• US EPA · Section 608 technician certification ↗Technicians who service equipment that could release refrigerant must be certified.
• US EPA · Refrigerant sales restriction ↗Refrigerant for stationary systems is sold to certified technicians and their employers.
• US EPA · Stationary refrigeration resources for homeowners ↗R-22 phaseout and the warning about flammable "22a" refrigerants.
• International Code Council · Code essentials: condensate ↗Automatic appliance shut-off accepted as protection against a blocked condensate drain.