AC not cooling? 8 things to check before you call a tech

Published April 25, 2026 · By the Pomona Valley Plumbing HVAC team

It is 95 degrees outside. You walk into your house expecting relief and the air coming out of the vents feels... warm. Or barely cool. Or like the system is running nonstop but the house will not get below 80.

Before you call us (or anyone), there are a few things worth checking. Some of them are free fixes you can do yourself in 5 minutes. Others will at least help you describe the problem accurately when you do call, which saves time and money.

1. Check the air filter

This is the number one cause of AC problems we see on service calls, and it is the one thing most homeowners forget about. A clogged air filter chokes off airflow to the evaporator coil. When the coil does not get enough warm air blowing across it, it gets too cold and eventually freezes solid. Once it is frozen, no cool air can get through.

Pull out your filter and hold it up to a light. If you cannot see through it, replace it. A new one costs $5 to $15 at Home Depot or Lowe's. If you see ice on the indoor unit after pulling a dirty filter, turn the system to "fan only" for 2 to 3 hours to let it thaw, then put the new filter in and switch back to cooling.

2. Look at your thermostat

It sounds obvious, but we get calls where someone accidentally bumped the thermostat to "heat" or "fan only." Check that it is set to "cool" and the temperature is set below the current room temp. If you have a programmable thermostat, check that the schedule did not revert to a default setting after a power outage.

If the thermostat screen is blank, try replacing the batteries. Some wired thermostats do not have batteries, so a blank screen on those usually means a tripped breaker or a blown fuse at the air handler.

3. Check both breakers

Your AC system uses two breakers: one for the indoor air handler (or furnace) and one for the outdoor condenser. They are usually in different spots on your breaker panel. If the outdoor breaker tripped, the fan inside will still blow air, but it will be room temperature air because the compressor is not running.

Flip both breakers fully off, wait 30 seconds, then flip them back on. If one trips again immediately, do not keep resetting it. That means there is an electrical issue that needs a technician.

4. Go look at the outdoor unit

Walk outside and look at your condenser. Is the fan spinning? If the fan is not running but you can hear humming, the fan motor or capacitor might be dead. If the unit is completely silent, it is probably a breaker or contactor issue.

While you are out there, check if anything is blocking the unit. Overgrown bushes, leaves, patio furniture, or a pool cover stored against the unit can restrict airflow enough to cause problems. The condenser needs about 2 feet of clearance on all sides.

5. Check the condensate drain

Your AC pulls moisture out of the air and drains it through a small PVC pipe, usually routed to the outside of the house or to a floor drain. If that drain line clogs (algae buildup is common in our climate), the drain pan fills up, and many systems have a safety float switch that shuts the whole system down to prevent water damage.

Find where the drain line exits your house. If water is not dripping out while the AC runs, the line might be clogged. You can try pouring a cup of white vinegar into the drain pan access point to clear a minor clog. If that does not work, it needs to be blown out with compressed air or a wet vac.

6. Check if the supply vents are open

Walk through the house and check every supply vent. We have been on calls where 3 or 4 vents got closed at some point, maybe during winter or when rearranging furniture, and nobody reopened them. Closing too many vents increases pressure in the ductwork and forces the system to work harder while delivering less total cooling.

7. Consider the age and condition of your system

If your AC is 12 to 15+ years old and this is the second or third problem this year, the compressor or refrigerant system might be failing. Older systems that use R-22 (Freon) refrigerant are especially expensive to repair since R-22 has been phased out and the remaining supply is expensive.

We can still repair many older systems, but at some point the math favors installing a new system over paying $500 to $1,000 per repair visit. We will be straightforward with you about where that line is.

8. Check if it is actually the hottest part of the day

This one catches people off guard. Most residential AC systems are designed to cool the house 20 to 25 degrees below the outside temperature. On a 110°F day in Pomona, your AC working at full capacity might only get the house down to 85 to 90°F in the peak afternoon hours. That does not necessarily mean anything is broken. It means the system is at its limit.

If the house cools down to the set temperature by evening and stays comfortable overnight, your system is probably working fine. Close blinds on south and west facing windows during the afternoon to help it out.

When you should skip the checklist and just call

Some situations need a technician right away:

• You smell something burning or electrical coming from the unit
• The outdoor unit is making a loud grinding or screeching sound
• You see ice on the outdoor refrigerant lines (the thicker insulated pipe)
• The breaker trips repeatedly after resetting
• You have elderly family members, infants, or pets and the house is above 90°F inside

For those situations, give us a call at 909-764-3214. We do same-day AC repair in Pomona and surrounding areas, and we do not charge overtime or weekend rates.