If your air conditioner has been running almost nonstop this week and your house still feels warm, you are not imagining things. When temperatures push past 100 degrees across Murrieta, Temecula, and Vista, every AC system in the region gets tested. This is the time of year our phones ring the most. After more than 20 years servicing homes across Riverside and San Diego counties, our NATE-certified technicians see the same handful of issues every summer. Here is how to tell the difference between normal heat stress and a real problem.
The 20-Degree Rule: What a Healthy AC Should Actually Do
A properly working central air system is not designed to make your house feel like a walk-in freezer on a 105-degree day. Its job is to cool the air passing through it by about 18 to 22 degrees compared to the air going in. That means if the air entering your return vent is 100 degrees, air coming out of your supply vents around 78 to 82 degrees is actually normal performance, even though the house may still feel warmer than you would like.
Here is a simple check anyone can do. Hold a thermometer near a return air grille, then near a supply vent in another room. If the difference is close to 20 degrees, your system is doing its job. The heat outside is simply winning. If the difference is much smaller, something is actually wrong.
Six Reasons Your AC Can’t Keep Up Right Now
A dirty air filter A clogged filter blocks airflow across the indoor coil. Less air moving across the coil means less heat gets removed from your home, and in bad cases the coil can freeze solid, which makes cooling stop altogether. This is the single most common cause of a struggling AC, and it is also the easiest to fix.
A dirty outdoor condenser coil The unit outside your home dumps heat from inside your house into the outside air. Dust, pollen, and debris from Santa Ana wind events build up on those coil fins over the summer. A dirty coil cannot release heat efficiently, so the whole system works harder for less cooling.
Low refrigerant from a leak Refrigerant does not get used up like fuel. If a system is low, it is losing refrigerant somewhere through a leak. A system running low struggles to pull heat out of your home no matter how hard it runs, and the problem gets worse, not better, over time.
A system that was sized for an average day, not a heat wave Some homes in Murrieta, Temecula, and Vista have systems that were sized correctly on paper but are now working against additional attic heat, aging insulation, or added square footage. On a 75-degree day, an undersized system can keep up just fine. On a 108-degree day, the same system may fall behind by several degrees no matter what you do.
Closed vents in unused rooms Closing vents to save energy is one of the most common habits we see, and it usually backfires. Central systems are designed around a certain amount of airflow. Closing too many vents raises pressure in the ductwork, which can reduce total airflow and stress the system.
Leaky ductwork in the attic A Southern California attic can reach 140 degrees or more on a summer afternoon. If your ducts have gaps or disconnected sections up there, conditioned air is escaping into the attic and hot attic air is being pulled into the system before it ever reaches your rooms.
What Is Just Normal Heat Stress, Not a Repair Issue
Some things that feel alarming during a heat wave are actually expected. A system running almost continuously during the hottest part of the afternoon is normal on extreme days. Taking longer than usual to pull the house down a few degrees after being off is normal. A noticeable difference between how the house feels at 4pm versus 9pm is normal, since the sun load on the roof and windows changes throughout the day. None of these things mean the system is broken. They mean the system is working exactly as hard as it should.
Quick self-check before you call anyone
- Replace or check the air filter, it should not be visibly gray or clogged.
- Walk outside and clear leaves, dirt, or plants away from the condenser unit.
- Confirm the thermostat is set to Cool, not Auto, with the fan set to Auto.
- Check that the breaker for the outdoor unit has not tripped.
- Open any vents you may have closed off in unused rooms.
When It’s Time to Call a Professional
Call for service if the difference between your return air and supply air is well under 15 degrees, if you notice ice on the refrigerant lines or indoor coil, if you hear grinding or squealing that was not there before, if you smell anything burning, or if your utility bill has spiked far beyond what the extra heat alone would explain. These are signs of an actual mechanical problem, not just tough weather.
Our technicians serve Murrieta, Temecula, and Vista, along with the surrounding Riverside and San Diego county communities, with same-day appointments during peak summer months. If your system is genuinely struggling and not just working hard, we would rather diagnose it properly than have you ride it out through August.
Written with Cool Air Solutions’ NATE-certified technicians, serving Southern California homeowners in Murrieta, Temecula, Vista, and surrounding communities for over 20 years.
