AC Running But Not Cooling the House

Your AC sounds like it's working — the fan is blowing, the outdoor unit is humming — but the temperature inside keeps climbing. This is one of the most frustrating HVAC problems, especially when Austin hits triple digits and your system can't keep up. The cause is usually one of a few common issues, some fixable in minutes and others requiring a technician.

Key Takeaways

Replace the air filter and rinse the outdoor condenser coils with a garden hose first — these two DIY steps resolve many cases of an AC that runs but won't cool.
During extreme Austin heat (105+), most residential AC can only maintain about a 20-degree differential from outdoor temps — running continuously at that point is normal, not a malfunction.
Duct leaks in unconditioned attic space are a hidden culprit: the average home loses 20-30% of cooled air through duct gaps, with attic temps reaching 150 degrees in summer.
Close blinds on south- and west-facing windows, run ceiling fans, and avoid using the oven during peak afternoon heat to reduce the load on your system.

Possible Causes

Dirty condenser coils (outdoor unit) DIY Fix

The outdoor unit releases heat absorbed from inside your home. When the condenser coils get coated with dirt, cottonwood fluff, grass clippings, or Austin's ubiquitous live oak debris, they can't dissipate heat efficiently. The system runs but can't complete the cooling cycle.

Low refrigerant charge Call a Pro

Refrigerant is the chemical that carries heat from inside to outside. If a leak has reduced the charge, your system will run continuously without ever reaching the set temperature. You might notice the supply air is slightly cool but not cold.

Severely clogged air filter DIY Fix

A filter that's been neglected for months (especially through Austin's cedar season from December through February) can reduce airflow so much that the evaporator coil can't absorb enough heat. The system runs but delivers warm or lukewarm air.

Duct leaks or disconnected ductwork Call a Pro

Many Austin homes have ductwork running through unconditioned attic space where temperatures can reach 150 degrees in summer. If ducts have gaps, disconnections, or deteriorated insulation, cooled air escapes into the attic before reaching your rooms.

Undersized system or extreme heat Call a Pro

When Austin sees sustained temperatures above 105, even properly functioning systems struggle. Most residential AC is designed to maintain a 20-degree differential from outdoor temps. At 108 outside, holding 88 inside may be the best it can do.

What to Do Right Now

Replace the air filter if it hasn't been changed in the last 30 days.
Go outside and look at the condenser unit — if the fins are caked with debris, gently rinse them with a garden hose (not a pressure washer).
Close blinds and curtains on sun-facing windows to reduce heat load.
Make sure all supply vents inside are open and not blocked by furniture.
If the system has been running for hours without progress, turn it off for 15 minutes to let the coils thaw if there's any ice buildup, then restart.

Get Same-Day Help From a Licensed Contractor

Frequently Asked Questions

Why is my AC running but not cooling my house?

The most common reasons are dirty condenser coils, a clogged filter, low refrigerant, or duct leaks. Start with the filter and the outdoor unit — those are things you can check and fix yourself in minutes.

Why can't my AC keep up when it's really hot outside?

Residential AC systems are typically designed to maintain about a 20-degree temperature difference from outside. During Austin's most extreme heat (105+), your system may run continuously and still not reach your preferred temperature. That's within normal operating range for most units.

How can I help my AC cool better in Austin summers?

Change filters monthly, keep the outdoor unit clear of debris, close blinds on south and west windows, run ceiling fans to circulate air, and avoid using the oven during peak afternoon heat. If your system is 12+ years old, it may be time to consider a higher-efficiency replacement.