AC Unit Not Cooling Your Home? Start Here

It's the second 90°F day in a row in San Jose, the AC is running but the house won't cool, and the unit just sounds like an expensive paperweight. Before you call anyone, here's what to check, in the order I check it.

Step 1: change the air filter

Half of "my AC isn't cooling" calls — genuinely — get fixed with a clean filter. A clogged filter starves the system of airflow, the indoor coil ices over, and the unit blows warm because it can't move enough air across the cold coil. Replace the filter, run the system in fan-only for an hour to thaw any ice, and try again.

Step 2: check the thermostat

Set the thermostat to "cool" and 5°F below current room temp. If the screen is blank or behaving oddly, replace the battery. On smart thermostats (Nest, Ecobee), confirm the schedule isn't overriding your manual setting.

Step 3: walk to the outside unit

Is the condenser fan spinning? You should hear and see it. If the unit is silent, the breaker may have tripped — check the electrical panel and the disconnect on the side of the house. If the fan is spinning but no air is coming out of the vents inside, the indoor blower is the suspect.

Step 4: clean the outside coils

The outdoor unit needs to dump heat into the air. If the coils are caked with dust, leaves, or cottonwood (Bay Area: this is a thing in late spring), the unit can't reject heat efficiently and the cooling output drops. Spray the outside of the coils gently with a hose — never high-pressure. Don't bend the fins.

What needs a pro

• Low refrigerant. If the system is short on refrigerant, it has a leak — refilling without finding the leak just buys you a few weeks. Refrigerant handling requires EPA certification.
• Failed capacitor. The most common AC repair we do, hands down. Symptom: outside fan won't spin, or hums for a few seconds and stops. $200–$300 fix on average.
• Bad contactor. Outside unit won't even try to start. Quick fix.
• Compressor failure. The big-ticket repair. On older units this is often the moment to look at replacement instead.

We do AC repair across the Peninsula on split, window, portable, and packaged units. Same-day service is normal during heat waves — we extend the day to handle them.

House getting hot? Call (650) 691-3065 and we'll get to you today.