Few things are worse on a 100-degree day in the San Fernando Valley than an air conditioner that runs but blows warm air. The good news: some causes are simple to fix yourself. Others need a licensed technician. Here are the most common reasons we find when we answer “AC blowing warm air” calls across Los Angeles.
1. Thermostat settings
Make sure the thermostat is set to Cool, the set temperature is below the room temperature and the fan is on Auto. With the fan on On, the blower keeps running even when the outdoor unit is off, which can feel like warm air. Replace batteries if the display is dim.
2. A dirty air filter
A clogged filter restricts airflow, reduces cooling and can even cause the indoor coil to freeze. Check the filter first — it is the cheapest fix there is. In Southern California, dust, pets and wildfire smoke can clog filters quickly.
3. The outdoor unit is not running
Go outside and check the condenser. If the indoor fan runs but the outdoor fan and compressor are silent, check for a tripped breaker or a pulled disconnect near the unit. If power is fine, a failed capacitor or contactor is one of the most common summer repairs we make — especially after a heat wave.
4. A dirty outdoor coil
The outdoor coil releases heat from your home. When it is covered in dust, leaves, grass clippings or cottonwood fluff, the system cannot shed heat and cooling drops. Keep at least two feet of clear space around the unit. Gentle rinsing with a garden hose (power off) can help; a professional cleaning is more thorough.
5. Low refrigerant from a leak
Air conditioners do not “use up” refrigerant. If the charge is low, there is a leak. Signs include warm air, ice on the refrigerant lines, hissing sounds and longer run times. Adding refrigerant without finding the leak is a temporary fix at best. A technician should locate the leak and recommend the right repair.
6. A frozen evaporator coil
Restricted airflow or low refrigerant can make the indoor coil freeze. Airflow drops and warm air comes from the vents. Turn the system to Off and the fan to On to let the ice melt, replace the filter, and call for service if it happens again. See why your AC freezes up for more.
7. Leaky ductwork
If some rooms cool and others do not, ducts in the attic may be leaking or disconnected. In summer, LA attics can reach 130–150°F, so leaking ducts pull in very hot air.
8. A worn-out compressor or an aging system
If your AC is 12–15 years old or more and has had several repairs, a failing compressor may be the cause. Older systems using R-22 refrigerant are especially expensive to repair. At that point it is worth comparing repair against replacement — read our guide on whether to repair or replace.
When to call a pro
If you have checked the thermostat, filter, breaker and outdoor unit and the air is still warm, it is time for professional AC repair. Do not keep running a system that is iced up or making grinding or buzzing sounds — that can damage the compressor.
Need cool air today?
Orion HVAC serves La Crescenta, Glendale, Burbank, La Cañada Flintridge, Tujunga, Santa Clarita and the San Fernando Valley. Call (323) 736-3737 or book online. You get the price before any work begins, and every repair is backed by our parts and labor guarantee.
