AC problems • Troubleshooting guide
AC Running but Not Cooling? Here’s What It Could Mean
The fan runs, the thermostat says cool, and the air from the vents is barely cooler than the room. Here is what usually causes it and what to do first.
Or dial (213) 214-0220 — available 24/7.
The short answer
An air conditioner that runs but does not cool is one of the most common AC problems in Los Angeles, and the cause is often simple. Start with the thermostat: it should be set to Cool, not Fan or Heat, with a set point below the room temperature. Next, look at the filter. A filter clogged with dust chokes airflow so badly that the indoor coil cannot absorb heat, and the air arriving at the vents feels almost room temperature.
If both are fine, go outside. The outdoor unit should be humming with its fan turning. A silent outdoor unit while the indoor blower runs points to a failed capacitor, a tripped disconnect or a control problem. A running outdoor unit with warm air indoors often means a refrigerant leak or a coil that has iced over. Those need a technician; nothing on this page asks you to open the equipment.
Most common causes
-
Thermostat set to the wrong mode
Fan mode moves air without cooling it, and a set point above the room temperature never calls for cooling. It sounds obvious, but after a power blip or a guest fiddling with it, it happens constantly.
-
A clogged air filter
When the filter is packed with dust, too little air crosses the indoor coil. The coil gets too cold, may ice up, and the little air that does get through is not cooled properly.
-
Outdoor unit not running
If the condenser fan and compressor are not running, the system cannot dump heat outside. A failed run capacitor, a blown fuse in the disconnect or a contactor problem are the usual reasons.
-
Low refrigerant from a leak
Refrigerant does not get used up; if it is low, it leaked. With too little refrigerant the coil cannot absorb enough heat, so the air feels cool at best and warm at worst, and the system runs for hours.
-
Dirty condenser coil
Years of leaves and dust and grass clippings insulate the outdoor coil. Heat cannot escape, pressures climb, and cooling drops off, especially on the hottest afternoons.
-
Leaky or disconnected ductwork
In many Los Angeles attics the ducts run through air well over 120°F. A split duct or a fallen boot dumps cold air into the attic and pulls hot air in, so the rooms never catch up.
Safe checks before you call
None of these involve opening the equipment, touching wiring or bypassing a safety switch. If a check needs a tool or a panel removed, it is not on this list on purpose.
-
Read the thermostat
Confirm it says Cool, the set point is at least 3°F below the room temperature, and the display is not blank or showing a low-battery icon.
-
Look at the filter
Slide the filter out of its slot at the return grille or air handler. If you cannot see light through it, replace it with the same size and note whether the air gets colder over the next hour.
-
Check that vents and returns are open
Furniture, rugs and closed dampers on supply registers reduce flow. Make sure the large return grille is not blocked by a door or a bookcase.
-
Listen and look at the outdoor unit
From a safe distance, note whether the fan is turning and the unit is humming. Clear leaves and clutter from around it so air can move, without removing any panel.
-
Feel the vent air after a quarter of an hour of running
If it is noticeably cooler than the room but the house is not catching up, the problem is more likely airflow, ducts or a dirty outdoor coil than a total failure.
Stop and call if…
How an AC24Repair technician diagnoses this
The technician starts with the two cheapest explanations, thermostat and airflow, because they are the most common. Then they measure how much heat the system is actually removing by comparing the air temperature going into the indoor unit with the air coming out. A small difference with good airflow points toward refrigerant; a large difference with weak airflow points toward the filter, blower or ducts.
At the outdoor unit they check whether the compressor and fan are running and drawing normal current, inspect the coil, and connect gauges to read the refrigerant pressures. If refrigerant is low, they look for the leak rather than just adding more, because a top-up without a repair fails again within weeks. You get a plain explanation of the cause and the price of the fix before anything is done.
Repairs that may follow the diagnosis
Which one applies, and what it costs, depends on what the technician finds. You hear the price before any work starts.
-
Filter, blower or duct airflow repair
Replacing a collapsed filter, cleaning a blower wheel, reattaching a fallen duct or sealing a split one restores the airflow the coil needs.
-
Capacitor, contactor or fuse replacement
When the outdoor unit is not starting, a failed capacitor or contactor is a routine part swap that gets the compressor running again.
-
Refrigerant leak repair and recharge
The technician finds the leak, repairs or replaces the leaking section, pulls a vacuum and recharges the system to the correct amount.
-
Condenser coil cleaning
A thorough cleaning of the outdoor coil brings pressures back to normal and often restores cooling capacity that had faded over several summers.
Clear pricing before the work starts.
Diagnostic visit fees depend on the time of day. We publish the confirmed diagnostic fees and explain the repair price before work begins.
Help with this across Los Angeles
Technicians come to homes in the San Fernando Valley, West, Central and Northeast Los Angeles.
AC not cooling: questions homeowners ask
Why does my AC cool at night but not in the afternoon?
During the hottest hours the system has to remove far more heat. A dirty outdoor coil, low refrigerant or leaky attic ducts show up first as afternoon failures because the margin is gone. The diagnostic visit measures where the capacity is being lost.
Can I just add refrigerant myself?
No. Refrigerant is a regulated substance that requires licensed handling and the right equipment, and adding it without fixing the leak wastes money. Leave refrigerant to the technician.
How long should I wait after changing the filter?
Give the system about an hour of continuous running. If the coil had started to ice, it also needs time to thaw. If the air is still not cold after that, book a visit.
Is warm air from the vents dangerous?
On its own, no. It becomes a safety issue if it comes with a burning smell, a tripped breaker or ice on the lines, in which case switch the system off and call.
Will you tell me the repair price before fixing it?
Yes. After the diagnosis the technician explains what is wrong and what the repair costs, and only starts work when you approve it.
Tell us what’s happening. We’ll take it from there.
Call any time. We schedule a technician within 24 hours and explain the price before repair work starts.
Or dial (213) 214-0220 — available 24/7.