The fan is running, but the air from the vents is warm. Or the house cools a little and then gives up by mid-afternoon.
When an AC is not cooling, the cause can be anything from a thermostat setting to a failed part. Some of it you can check yourself quickly, with no tools and no opening of panels. This guide goes through those checks in order, and then explains what a contractor tests when they do not solve it.
Air Conditioning Repair San Diego is an independent referral service, not an air conditioning or HVAC company. Calls and form requests are passed to an independent local AC and HVAC contractor, who can contact you about your system; that contractor gives any quote and does any work.
Check the thermostat
Start at the wall. Make sure the thermostat is set to cool, not heat or fan, and that the setting is lower than the room temperature. If the fan is set to on rather than auto, it blows air all the time, even when the system is not cooling, which can feel like warm air from the vents. Replace the batteries if the thermostat uses them, and check that the screen is not blank.
Check the breaker
Look in the electrical panel for a tripped breaker for the air conditioner or the furnace. Reset it once. If it trips again, leave it off and call: a breaker that keeps tripping is telling you something is wrong.
Check the air filter
A clogged filter starves the system of air, and a system without enough air cannot cool well. ENERGY STAR says to inspect, clean or change the filter once a month in a central air conditioner, furnace or heat pump, and warns that a dirty filter can increase energy costs and damage the equipment, leading to early failure. If the filter is grey and matted, change it. The article how often to change your AC filter covers it in more detail.
Check the condensate drain
An AC pulls water out of the air, and that water drains away through a line from the indoor unit. If the drain is plugged, water can back up. ENERGY STAR notes that a plugged drain can cause water damage in the house and affect indoor humidity. Look for water in the drain pan or on the floor around the indoor unit.
Check the outdoor unit
Go outside while the system is calling for cooling. The outdoor unit’s fan should be turning. Clear leaves, boxes and plants away from it so air can move through. If the unit hums but the fan does not turn, or it is silent while the thermostat calls for cooling, switch the system off at the thermostat and call.
Look for ice
Ice on the refrigerant lines or the indoor coil often points to an airflow or refrigerant problem. Switch the cooling off and let the ice melt before anyone works on the system. A clogged filter is one common cause; if the filter is clean, the system needs testing.
What not to do
Do not add refrigerant, open the sealed system or take panels off the outdoor unit. Under EPA Section 608, technicians who maintain, service or repair equipment that could release ozone-depleting refrigerants must be certified.
What a contractor tests next
If the checks above do not bring the cooling back, the system needs testing. ENERGY STAR’s check-up list shows the parts a contractor looks at: the thermostat settings, the electrical connections and the voltage and current on motors, the condensate drain, the controls and the starting cycle, the evaporator and condenser coils, the refrigerant level, and the blower. Too much or too little refrigerant makes a system less efficient, and airflow problems can reduce efficiency by up to 15 percent. Ask for the cause and the repair in writing before work starts.
If the AC failed in very hot weather, see the San Diego heat wave guide for the County’s Cool Zones; if someone shows signs of heat stroke, call 911. For the repair itself, the homepage guide to air conditioning repair in San Diego explains how a repair visit works. This site is about home air conditioning. For a car’s AC, an auto repair shop is the place to ask.
Still not cooling? Call the number on this page or send the form, and an independent local AC contractor can contact you.
Questions people ask
Why is my AC running but not cooling?
Check the thermostat mode and setting, the breaker, the filter, the condensate drain and the outdoor unit. If those are fine, the system needs testing by a contractor.
How do I reset my air conditioner?
Turn the system off at the thermostat, reset a tripped breaker once, then turn it back on. If the breaker trips again, leave it off and call.
Can a dirty filter stop my AC from cooling?
Yes. A clogged filter starves the system of air. ENERGY STAR says a dirty filter can raise energy costs and damage the equipment.
Can I add refrigerant myself?
No. Under EPA Section 608, technicians who service equipment that could release ozone-depleting refrigerants must be certified.
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