Air Conditioner Running But Not Cooling?
Answer a few questions and Fixly Guide will help you understand what may be happening, how urgent it is, and whether this is a repair or a replacement conversation.
Stop and Get Help If You See This
Treat it as urgent if you see:
- A burning, electrical, or hot-plastic smell from the unit or vents
- Repeated breaker trips when the system starts
- Smoke, sparking, or scorched wiring at the outdoor unit
- Indoor temperatures becoming unsafe for infants, elderly, or medically vulnerable people
- Water pooling near electrical components or the furnace/air handler
Shut the system off at the thermostat and the breaker if you smell burning or see sparking, and do not keep resetting a breaker that trips repeatedly.
Quick answer
An air conditioner that runs but does not cool almost always has a specific restriction or failed component rather than a system that simply 'wore out.' Airflow problems (dirty filter, blocked coil, closed vents), refrigerant leaks, electrical component failures, and thermostat faults cover the large majority of cases. Which one it is depends on the system's age, whether there is ice, and whether the outdoor unit is running — which is exactly what the assessment walks through. This page is educational information, not a diagnosis of your system.
Possible causes
Dirty or clogged air filter
A restricted filter chokes airflow across the coil and is the single most common cause of weak cooling.
Frozen evaporator coil
Low airflow or low refrigerant can ice the indoor coil — the system runs, but almost no cold air moves.
Refrigerant leak
Refrigerant is not consumed. If the charge is low, there is a leak that has to be found and repaired.
Failing capacitor or contactor
A weak start capacitor is a common, inexpensive failure that keeps the compressor or fan from running properly.
Dirty outdoor condenser coil
Grass clippings, cottonwood, and dust blanket the coil so the system cannot reject heat outside.
Thermostat or wiring fault
A miscalibrated, mis-wired, or dead-battery thermostat can leave the blower running with no cooling call.
Blocked or leaking ductwork
Cool air produced at the unit can be lost into an attic or crawlspace before it reaches rooms.
Failing compressor
On older systems, a failing compressor is the point where replacement usually enters the conversation.
Undersized or aging system
A system past 12–15 years often loses capacity gradually rather than failing outright.
Clogged condensate drain
A full drain pan can trip a safety switch and shut cooling down entirely.
How this project is usually classified
General guidance for this problem type — not a diagnosis of your home.
- Typical urgency
- Urgent — within days
- Safety risk
- Moderate safety risk
- DIY suitability
- Pro recommended
- Cost level
- Moderate cost
- Repair option
- Capacitor, contactor, or leak repair on a system with remaining service life.
- Replacement option
- Replacement when the compressor fails or the system uses obsolete refrigerant.
- Typical timeline
- Same-day diagnosis in season; replacement 1–2 days
- Contractor type
- hvac
What you can safely check yourself
- Replace the air filter if it is dirty, then give the system an hour to recover.
- Confirm the thermostat is set to COOL, the fan to AUTO, and the batteries are good.
- Look at the outdoor unit: is the fan spinning and is the coil clear of grass, leaves, and debris?
- Check for ice on the refrigerant line or indoor coil — if you see ice, switch to FAN only and let it thaw.
- Make sure supply and return vents are open and unblocked throughout the house.
- Check the breaker for the air handler and the condenser.
Before the pro arrives
- • Know the system age, brand, and model number from the outdoor unit label.
- • Note the indoor temperature versus the thermostat setting over the day.
- • Have any recent service or repair records available.
- • Mention whether the problem is constant or only during the hottest hours.
Questions to ask
- • What exactly failed, and how did you verify it?
- • If refrigerant is low, where is the leak and what does repairing it cost?
- • Given this system’s age, what is the realistic remaining life after this repair?
- • What is the repair warranty, on both parts and labor?
- • What would a replacement cost, and would it change my utility bills?
Common questions
Why is my AC running but not cooling?
The most common causes are a clogged filter, a frozen evaporator coil, low refrigerant from a leak, a dirty outdoor condenser coil, or a failed capacitor. Airflow problems account for a large share of "runs but does not cool" calls.
Should I add refrigerant myself?
No. Refrigerant is not consumed during normal operation, so low charge means a leak. Adding refrigerant without repairing the leak wastes money and can damage the compressor. It is also regulated work in most areas.
What do I do if the coil or line is iced over?
Switch the thermostat to OFF for cooling and set the fan to ON so the coil can thaw, then replace the air filter. If it ices again after thawing, the system needs a professional diagnosis.
When does an AC repair stop making sense?
Generally when the system is past roughly 12–15 years, the repair involves the compressor or a significant refrigerant leak, or repair costs approach a large share of replacement. Age plus repeat failures is the deciding pattern.
Keep reading
Other common home problems
Start with the symptom and get likely causes, safety guidance, and a next step.
Fixly Guide provides educational guidance only. Nothing here is a professional diagnosis, an inspection, or a guarantee of contractor availability or pricing.