Why Is My AC Not Cooling in Houston?

When your AC is running but your home won't cool down, something is wrong. Here's how to troubleshoot the most common causes — and when to call a pro.

By Multipoint AC & Heating | Serving Greater Houston

It's the middle of summer, the thermostat is set to 72°F, and your AC has been running for hours — but your house still feels like an oven. If you're a Houston homeowner, this scenario is all too familiar. The good news is that most AC cooling problems come down to a handful of common causes, and some of them you can fix yourself in minutes.

Here's what to check first, and when it's time to call Multipoint AC & Heating.

1. Dirty or Clogged Air Filter

This is the number one cause of AC cooling problems we see across Houston, and it's also the easiest to fix. A clogged filter restricts airflow through your system, which means your AC is running but barely moving air through your home. In extreme cases, it can cause your evaporator coil to freeze over — which makes cooling even worse.

What to do: Pull out your air filter and hold it up to the light. If you can't see through it, replace it immediately. In Houston's climate, most homes need a new filter every 30 to 60 days during peak cooling season.

2. Frozen Evaporator Coil

If your AC is blowing warm air or very weak airflow, a frozen evaporator coil could be the culprit. This happens when airflow is restricted (often due to a dirty filter) or when refrigerant levels are low, causing the coil to ice over and stop transferring heat effectively.

What to do: Turn the system off and let it thaw for 2 to 3 hours with just the fan running. Check and replace the filter. If it freezes again after restarting, you likely have a refrigerant issue and need a technician.

3. Low Refrigerant / Refrigerant Leak

Your AC doesn't "use up" refrigerant like a car uses gas — it circulates in a closed loop. If refrigerant levels are low, it means there's a leak somewhere in the system. Low refrigerant means your AC physically cannot remove enough heat from your home, no matter how long it runs.

Signs of a refrigerant leak include:

• Warm air blowing from vents despite the system running

• Ice forming on the refrigerant lines or outdoor unit

• A hissing or bubbling sound near the unit

• Higher than normal electric bills

What to do: This requires a licensed HVAC technician. Refrigerant handling is regulated by federal law and cannot be a DIY fix. Call Multipoint AC & Heating for a leak diagnosis and recharge.

4. Dirty or Blocked Condenser Unit

Your outdoor condenser unit releases the heat pulled from inside your home. If it's clogged with dirt, leaves, grass clippings, or debris — or if it's surrounded by overgrown shrubs — it can't release heat efficiently, and your system's cooling capacity drops significantly.

What to do: Turn off the system and gently rinse the condenser coils with a garden hose from the inside out. Clear at least 2 feet of space around all sides of the unit. If the coils are heavily fouled, schedule a professional cleaning.

5. Thermostat Issues

Sometimes the problem isn't your AC at all — it's the thermostat. A thermostat that's incorrectly calibrated, placed in direct sunlight, or set to "fan only" instead of "cool" will cause your system to behave erratically or not cool at all.

What to do: Make sure the thermostat is set to COOL, not FAN or HEAT. Check that the set temperature is below the current room temperature. If you have an older thermostat, consider upgrading to a programmable or smart thermostat — it's a small investment that pays off in comfort and energy savings.

6. Undersized AC System

Houston summers are brutal. If your AC unit is too small for your home's square footage, it will run continuously and still struggle to cool your space — especially during heat waves when outdoor temperatures push above 95°F. This is a common problem in older Houston homes that have had additions or renovations without upgrading the HVAC system.

Signs your system may be undersized:

• The AC runs all day without ever reaching the set temperature

• Some rooms are always warmer than others

• Your energy bills are unusually high despite the system running constantly

What to do: Have an HVAC professional perform a load calculation to determine the right size system for your home.

7. Ductwork Leaks

Your ducts carry cooled air from your AC to every room in your home. If ducts are leaky, poorly insulated, or disconnected — which is common in older Houston homes — a significant portion of that cooled air never reaches its destination. Studies suggest leaky ducts can reduce system efficiency by 20 to 30 percent.

Signs of duct problems include:

• Rooms at the far end of the house that never cool properly

• High energy bills despite the system running well

• Dust buildup around vents

What to do: Schedule a duct inspection. Sealing and insulating ducts is one of the highest-return HVAC improvements a Houston homeowner can make.

8. AC System Is Too Old

If your system is 12 to 15 years or older and just isn't keeping up anymore, age may simply be the issue. Older systems lose efficiency over time, and no amount of maintenance will restore a unit that's past its service life — especially in Houston's demanding climate.

What to do: Use the $5,000 Rule (age × repair cost). If the number exceeds $5,000, replacement is likely the better investment. See our previous post for a full breakdown of how to make that decision.

Houston Pro Tip: Don't Wait Until It Breaks

In Houston, your AC is not a seasonal appliance — it's an essential system that runs nearly year-round. The worst time to discover a problem is during a heat wave when every HVAC company in the city is slammed with calls. Schedule a tune-up in the spring before peak cooling season, so any issues get caught and fixed before the summer heat arrives.

Still Not Cooling? We Can Help.

If you've checked the basics and your AC still isn't cooling your Houston home, it's time to call in a professional. At Multipoint AC & Heating, our certified technicians diagnose and fix AC cooling problems fast — across Houston, Katy, Sugar Land, The Woodlands, Pearland, Friendswood, Missouri City, Cypress, Humble, Pasadena, and the entire Greater Houston metro area.