Thermostat Working but AC Not Cooling? Here's What to Check

It's one of the most frustrating summer surprises: the thermostat clicks on, the system hums to life, air moves through the vents — and the house just keeps getting warmer. If your thermostat is working but your AC is not cooling, you're dealing with one of the most common service calls we run in Central Ohio every June. The photo above is a recent one: a New Albany homeowner's system was running but not cooling, so we put gauges on it, traced the problem, and had the house comfortable again the same day.

The good news is that an AC not cooling doesn't automatically mean an expensive repair. Several of the most common causes are things you can check yourself in ten minutes. Here's how to narrow it down.

Why is my thermostat working but my AC not cooling?

When the thermostat is doing its job — calling for cooling, turning the system on — but the air never gets cold, the problem is almost always downstream of the thermostat. The usual suspects, roughly in order of how often we find them:

• A dirty air filter — the single most common cause. A clogged filter chokes airflow, the system can't move enough air across the cold coil, and the air from the vents feels weak and barely cool.
• A frozen evaporator coil — restricted airflow or low refrigerant can ice the indoor coil over. Once it's a block of ice, almost no cooling reaches the house, even though everything sounds like it's running.
• A dirty or blocked outdoor unit — the condenser outside needs to shed heat. Cottonwood fluff, grass clippings, leaves, and shrubs crowding the unit make it run hot and cool poorly.
• Low refrigerant from a leak — refrigerant doesn't get "used up." If it's low, it leaked, and the system will run constantly without ever catching up. Hissing or bubbling sounds and ice on the copper lines are telltale signs. Our post How Do I Know if My AC Needs Coolant? covers this in detail.
• A failing capacitor or compressor — if the indoor fan runs but the outdoor unit won't start (or starts with a hum and click), a weak capacitor is a frequent culprit. These are professional repairs.
• Thermostat settings or placement — occasionally the thermostat really is the issue: set to ON instead of AUTO (so the fan blows even when the system isn't cooling), set to HEAT, or mounted where sunlight or a nearby lamp fools its sensor.

Quick checks before you call for AC repair

Run through these five steps first — they solve a surprising share of "AC running but not cooling" calls:

• 1. Check the thermostat settings. It should be set to COOL, the fan to AUTO, and the target temperature at least a few degrees below the room temperature.
• 2. Replace the air filter. If you can't remember the last time you changed it, change it. Hold it up to a light — if you can't see light through it, it's choking your system.
• 3. Check the power. Look for a tripped breaker in the panel and make sure the outdoor disconnect (the small box on the wall near the condenser) is switched on. A breaker that trips repeatedly is a sign to stop and call — don't keep resetting it.
• 4. Look at the outdoor unit. Clear leaves, grass, and debris from around it, and gently rinse the coil fins with a garden hose (system off). Keep at least two feet of clearance on all sides.
• 5. Look for ice. Ice on the copper lines or indoor coil means turn the system off and let it thaw completely — running it frozen can damage the compressor. If it freezes again after thawing, the system needs professional diagnosis.

One more habit worth keeping: when the AC shuts off, give it three minutes before turning it back on. That pause lets internal pressures equalize and protects the compressor from hard starts.

Why is my AC running but not cooling the house enough?

Sometimes the air is cool — just not cool enough. The system runs all day and the house hovers a few degrees above the setpoint. In Ohio's humid summers, that's often a capacity or efficiency problem rather than a breakdown: an aging unit losing ground, a duct leak dumping cold air into the attic, or a system that was undersized to begin with. High humidity makes it worse, because a struggling AC removes less moisture and 75 degrees feels like 85. We covered the humidity side of this in Preparing Your HVAC System for Ohio's Humid Summers.

If your AC is on and blowing but never quite gets there, our post Why Is My Air Conditioner On But Not Cooling? digs deeper into that specific pattern. And if the system is 12–15+ years old and falling behind every summer, it may be worth comparing repair costs against a new high-efficiency unit — Should I Repair or Replace My AC Unit? walks through that decision, and our team can quote a professional air conditioning installation sized correctly for your home.

What we check on a not-cooling service call

When a Bryant technician arrives for an AC that's running but not cooling, the diagnosis is systematic: we verify thermostat operation, measure the temperature drop across the coil, put gauges on the system to read refrigerant pressures (like the service call pictured above), test capacitors and electrical components, and inspect the coils and condensate drain. That's how we find the actual cause instead of guessing — and why an accurate diagnosis usually costs far less than parts-swapping or waiting for a full breakdown on the hottest week of the year.

A seasonal tune-up catches most of these problems before they leave you sweating. If your system hasn't been looked at this year, an air conditioning inspection now is the cheapest insurance you can buy for July.

When to call Bryant Heating & Cooling

If you've checked the filter, the settings, and the breakers and the air still isn't cold — or you see ice, hear hissing, or the breaker keeps tripping — it's time for a professional. Bryant Heating & Cooling provides air conditioning repair for all makes and models across Columbus and Central Ohio, including New Albany, Gahanna, Westerville, Newark, and the surrounding communities, with 24-hour emergency AC repair when the heat won't wait. Call (614) 855-9010 or visit the contact page to schedule service.