Fix the setting or the filter, then give it an hour
A clogged filter starves the coil of air and can freeze it. The Department of Energy says to clean or replace the filter every month or two in cooling season, and that a clean filter can cut the air conditioner's energy use by 5 to 15 percent.
What is probably happening
- The thermostat was on HEAT, OFF, or a schedule pushed the setpoint up. Someone else in the house may have changed it.
- A filter that has not been changed in months. Look for gray fuzz and no light through it.
- Either one makes the AC seem broken when it is not.
Do this in the next five minutes
- Set the thermostat to COOL, fan AUTO, and a temperature a few degrees below the room.
- Replace the filter with the same size, arrow pointing toward the unit. Write the date on the frame.
- Open every supply register and move furniture off the return grille.
- Wait an hour. If the air at the vents is cold and the room is dropping, you are done.
- If it still blows warm, go back and pick the next option: ice on the lines, or the outdoor unit.
Do not
- Do not set the thermostat far lower to speed it up. It cools at the same rate and just runs longer.
- Do not run the AC with no filter in. Dust goes straight onto the coil.
Who to call
No call needed unless it is still warm after an hour
This is a five-minute homeowner fix. If it does not work, an HVAC technician diagnoses the airflow or refrigerant side.
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What it should cost
$100 to $250
Service call fee if you do need a visit, national range
Source: Angi, HVAC repair cost, updated August 2026. View source
National published range, not a quote for your job. The full cost table for this trade is on the hvac page.
Ask this contractor, on the phone, before anyone comes out
Tap each one as you ask it.
- Does the service call fee come off the repair if I go ahead?
- What filter size and MERV rating does this unit want?
- Can you check the temperature split across the coil and tell me the number?
End the call if
- A recharge or a replacement quote before anyone has checked the filter and airflow.
- A diagnosis over the phone with no visit.