Short answer
If the indoor fan runs but the air is warm, check the thermostat, the air filter and whether the outdoor unit is running. An outdoor unit that hums but does not spin usually has a failed capacitor or fan motor. If everything runs but cooling is weak, a dirty coil, low refrigerant from a leak or a failing compressor are the likely causes.
Check these first
These are safe for any homeowner and fix some problems outright.
- Thermostat on Cool, fan on Auto, setpoint below room temperature
- Air filter clean
- Outdoor unit breaker and disconnect on
- Outdoor unit fan spinning and the unit humming normally
- Supply and return grilles open and unblocked
- No ice on the indoor coil or the large refrigerant line
Outdoor unit is not running properly
The outdoor condenser holds the compressor, fan and the electrical parts that start them. A weak run capacitor or a stuck contactor is the most common failure, especially in the first heat wave of the season after weeks of idle mild weather.
If the unit hums but the fan does not spin, turn it off at the thermostat. Running it this way can overheat the compressor.
Not sure it is safe to keep running? A local technician can check it today.
Call NowEverything runs but it barely cools
A coil clogged with dirt, leaves or cottonwood fluff cannot reject heat. Low refrigerant means a leak, since refrigerant is not used up. A worn compressor may run without moving enough heat.
A technician measures pressures and temperatures to tell these apart rather than guessing.
When it is urgent
Treat it as urgent during extreme heat if anyone at home is elderly, very young or medically vulnerable, or if you notice a burning smell, repeated breaker trips or loud grinding from the unit.
Related questions
Can I hose off my outdoor AC unit?
Gently rinsing the outside of the coil with the power off is generally fine. Do not use a pressure washer, which bends the fins, and do not open the electrical panel.
How do I know if it's the capacitor?
Typical signs are a humming outdoor unit with a fan that does not spin, or a fan that starts if nudged. Capacitors store a charge, so only a technician should test or replace them.
Why is my AC worse in the afternoon?
Peak outdoor temperatures and sun on the house increase load. A system that was borderline in the morning may fall behind by late afternoon, especially if the coil is dirty or refrigerant is low.
Services that fix this
Central AC Repair
Systems that will not start, will not cool, freeze up, short-cycle or leak water.
Central AC repair in Fountain ValleyRefrigerant Leak Repair
Find and fix leaks instead of topping up refrigerant every summer.
Refrigerant leak repair in Fountain Valley
Emergency AC Repair
No cooling during a heat wave, burning smells, or a system that keeps tripping breakers.
Emergency AC repair in Fountain ValleyThis guide is general information for homeowners, not a diagnosis of your system. For anything involving gas, carbon monoxide, electricity or active leaks, stop and call a qualified professional.
