Temperatures in Marin County often spike 10-20°F above surrounding areas, making a working air conditioner a must for comfort and safety. Homeowners in Novato typically rely on central split AC systems to beat the heat, but even the best systems can break down in the middle of summer, and it can be frustrating. That’s why understanding the common failure points can save money and time.
As local HVAC experts since 1986, John Owens Services knows how Novato’s microclimate can strain the cooling system. And it can range from a frozen evaporator coil after a refrigerant leaks, to a stubborn start-capacitor that won’t turn on the compressor.
In this blog, we will walk you through the most frequent causes of air conditioning unit breakdowns on hot days, so you can spot trouble early. We will also cover capacitor failures, contactor problems, refrigerant leaks, dirty coils, thermostat troubles, and electrical issues in detail so that you have a clear understanding of what can go wrong with your AC and when to call a professional.
Capacitors are among the most failure-prone parts of an AC system. These small electrical components store and release energy to start the compressor and fan. Over time or under extreme strain, a capacitor can weaken or burn out. When that happens, your outdoor condenser won’t even turn on, and neither the fan nor the compressor can start without it.
The signs of capacitor failure include a humming sound from the condenser, intermittent operation (the AC kicks off and on rapidly), or the unit refusing to run at all. When you are troubleshooting, you must always check the capacitor with a multimeter or have an HVAC professional test it. Replacing a bad capacitor usually runs a few hundred dollars and is far cheaper than an overall AC replacement. So, if your AC blinks or won’t start on a hot day, call an HVAC technician because it is often the capacitor.
The contactor is essentially a high-voltage switch that connects power to the compressor and fan. These contacts can wear out, pit, or even weld shut over the years of use. A stuck or pitted contactor is one of the top reasons condensers won’t shut off or start properly. For example, if the contacts are welded closed, the outside unit may run continuously, and if the contacts fail to close, nothing happens when the thermostat calls for cooling.
Fixing a stuck contactor may be as simple as tapping or cleaning it with a wire brush, but this is only a temporary fix. Ultimately, a worn contactor should be replaced typically every 2–3 years for heavy-use systems to ensure reliable operation. In summary, if your AC is running all the time or not at all, then a failing contactor is a likely reason.
Air conditioners rely on refrigerant to transfer heat out of your home. Refrigerant leaks or simply low refrigerant levels can cause big problems. When levels drop, the system can’t cool properly, often leading to frozen evaporator coils or a hard-starting compressor. The typical causes are corroded coils or loose service valves.
Some of the common warning signs can be hot air from vents, unusually long run cycles, ice building on the copper lines, or high electricity bills. If your AC unit suddenly stopped cooling on an extremely hot day, low refrigerant is a prime suspect.
A trusted HVAC technician will check for leaks, repair any holes, and recharge the correct amount of refrigerant. In short, do not ignore weak airflow or frost; call a technician to test the refrigerant and fix leaks.
Dirt, dust, and debris can disrupt the efficiency of the AC. Over time, condenser coils and evaporator coils get grimy and block heat exchange. Likewise, a clogged air filter chokes airflow, and your AC struggles to pull in warm air or dump heat outside. This can cause the unit to short-cycle, overheat, or freeze up, leading to higher energy costs.
Typically, regular maintenance solves most of this. Clean or replace filters every 1 to 3 months, and keep the outdoor unit’s coil clear of leaves and grime. That’s why you should always check vents and ducts, as even simple obstructions can cut airflow. During troubleshooting, if the AC turns on but isn’t cooling, check for airflow issues first.
Regular professional tune-ups like coil cleanings make sure your AC isn’t failing simply because it’s dirty.
A dead battery, loose wiring, or an outdated thermostat can stop the AC unit from producing cool air. For example, if the thermostat’s batteries die or its temperature sensor fails, it may not signal the AC to run. That’s why checking the thermostat is also a good idea when you are troubleshooting an AC unit. The batteries could be out, or the wire might be loose, or it could simply be time for a new thermostat.
So if your AC is unresponsive, always confirm that the thermostat is set to cool and the temperature is below room level. Replace the batteries and make sure the display is working. In some older systems, there’s even a fuse or switch in the furnace or air handler, so check your home’s electrical panel or an emergency shutoff near the furnace. If the AC still won’t react, the thermostat itself might need replacement.
Modern AC units have many electrical parts beyond the capacitor and contactor, like transformers, relays, control boards, wiring harnesses, etc. Loose or burnt wires, blown fuses, or tripped breakers can instantly cause an AC to fail. That’s why you should always check if the circuit breaker tripped or a fuse blew. If so, resetting it may restore power. The outdoor unit also has a safety disconnect switch; make sure it’s in the “on” position.
If the AC still won’t power up, internal wiring or components may have failed. After checking breakers, call an HVAC professional rather than dealing with live circuits yourself.
Before your AC completely breaks down, there are some common signs. And being able to recognize these signs early can help you troubleshoot the problem.
Here are the common signs you can look out for:
If your AC is not giving out cool air, and the airflow is also weak, then the most common causes are probably refrigerant leaks, dirty coils or air filters, or thermostat malfunctions.
If your AC is not turning on, then there might be a power issue. Check if the circuit breaker is tripped or if the thermostat setting is in cool mode before calling for help.
If there are unusual noises like grinding, screeching, or clanking from the air conditioner, then there might be a mechanical problem. Some of the possible causes can be loose or worn-out fan motors, capacitor or contactor failures, or debris inside the system.
If you are noticing water pooling around your AC unit, then it could be a possible sign of a clogged condensate drain, frozen coils, or a refrigerant leak.
If your AC is frequently turning on and off, then it is usually a sign of thermostat issues, a low refrigerant level, or overheated fan motors or compressor.
If your home is feeling more humid than usual and the indoor air quality is poor, then it could mean that the AC is not properly dehumidifying the air, the evaporator coils are dirty, or refrigerant is leaking.
There are a few things you must check after your AC unit has suddenly stopped working, and then call for AC services.
As mentioned earlier, make sure that the thermostat is on “cool” and the set temperature is lower than room temperature. Check your main electrical panel and look for any blown fuses in the breaker box or at the furnace. Many homes have a fused disconnect in the attic or basement for the AC, which can be replaced.
Furthermore, make sure that any dedicated AC power switch near the outdoor unit or inside the air handler is turned on. Sometimes, a clogged filter can also cause the AC to shut down for safety reasons. You can replace or clean it and make sure the supply vents in the house are open and unobstructed.
In California’s milder climate, a well-maintained central AC typically lasts 10-20 years. On average, you can expect around 12-17 years before a new AC installation. Factors like regular maintenance, usage patterns, and quality of AC installation can affect its lifespan. For example, high-usage households or neglected units may fail earlier. To maximize life, you should replace filters routinely, keep the coil clean, and have annual tune-ups.
The capacitor is the most common part to fail on an AC unit. It gives motors the initial jolt to start, and when it weakens or shorts out, the compressor and fans do not turn on.
Always start with the thermostat and power supply. Make sure the thermostat is set to cool and has fresh batteries. Then check that the circuit breaker or fuse for the AC has not tripped. If the AC still won’t run, call for air conditioning repair services to inspect components like the capacitor or contactor.
Central AC units generally have a fused disconnect box near the outdoor condenser and a circuit breaker in the electrical panel of the home. Some air handlers also have a small fuse or reset button on the control board. If you suspect a blown fuse, turn off the power and remove the disconnect cover to inspect.
Besides electrical issues, the single most common failure is capacitor burnout. But in Novato’s heat, failure often stems from a combination of issues like refrigerant leaks, dirty coils, and worn electrical parts, which are all frequent culprits.
When your AC struggles to keep up with Novato’s summer heat, don’t wait until it’s unbearable. Professional HVAC service is essential for a safe, efficient, and lasting repair. DIY fixes can mask symptoms; certified technicians correctly diagnose issues, test refrigerant levels, verify electrical integrity, and make sure your system meets code. John Owens Services has been Novato’s trusted HVAC company for decades. Our fully licensed and highly trained team will thoroughly inspect your system, from the thermostat to the condenser, and fix problems right the first time.
Ready to stay cool? Schedule your Novato AC repair today with John Owens Services. Our Novato team is available 24/7 for emergency breakdowns and routine maintenance alike. We guarantee quality, on-time service, and upfront pricing. Don’t sweat another minute, call us or book service online now and get back to comfort!
Our philosophy is simple, we always want to maintain equipment to give it the longest life possible. Next, we want to focus on repairing when something goes wrong. Then only as the last choice, we replace equipment when needed. That’s the John Owens Way.
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