Why Is My AC Running But Not Cooling? (Causes & What to Do)

If your AC is running but your house isn’t getting cooler, the most common cause is a dirty air filter restricting airflow. Check your filter right now — if it looks gray, clogged, or you can’t remember the last time you changed it, swap it out and give the system 30 minutes. That fix is free and solves the problem about 25% of the time.

If the filter looks fine, keep reading. We’ll walk through every possible cause, from things you can check yourself to issues that need a technician.

Things You Can Check Right Now (No Tools Needed)

1. Check Your Air Filter

We put this first because it’s the #1 cause of AC problems, period. A clogged filter chokes your system. When airflow drops:

• The evaporator coil gets too cold and freezes
• The system runs constantly but can’t push enough cool air into your home
• Your energy bills spike

Replace it. Standard 1-inch filters should be changed every 30-60 days during summer in South Carolina. If you have pets, lean toward 30 days.

2. Check Your Thermostat Settings

Sounds obvious, but verify:

• It’s set to COOL (not heat, not fan-only)
• The fan is set to AUTO (not ON — “ON” runs the fan constantly, even when the AC isn’t actively cooling, which blows room-temperature air)
• The set temperature is below the current room temperature by at least 3-5 degrees
• The batteries aren’t dead (if it’s a battery-operated thermostat)

We’ve had service calls where someone accidentally bumped the thermostat to “heat” or a kid changed the settings. No judgment — it happens.

3. Check Your Outdoor Unit

Go outside and look at your condenser (the big box with the fan on top):

• Is it running? You should hear the fan and compressor humming. If it’s completely silent, there may be an electrical issue.
• Is it blocked? Bushes, debris, leaves, or a cover left on from winter will prevent heat dissipation. Keep 2 feet of clearance on all sides.
• Is the fan spinning? If the fan isn’t running but you hear a humming sound, the fan motor or capacitor may be failing.

4. Check Your Circuit Breakers

Your AC system typically has two breakers — one for the indoor unit (air handler/furnace) and one for the outdoor unit (condenser). If the outdoor breaker tripped, the indoor fan will still blow air, but it won’t be cool.

• Check your electrical panel
• If a breaker tripped, reset it once
• If it trips again, do NOT keep resetting it. Repeated trips mean there’s an electrical problem. Call a technician.

Common Causes That Need a Technician

Refrigerant Leak (Most Common Professional Repair)

Your AC doesn’t “use up” refrigerant like gas in a car. If it’s low, there’s a leak. Signs:

• System runs but blows lukewarm air
• Ice forming on the refrigerant line or evaporator coil
• Hissing or bubbling sound near the indoor unit
• Higher-than-normal electric bills

Cost to repair: $200-$1,500 depending on leak location and refrigerant type. R-410A is standard in newer systems. If you have an older R-22 system, refrigerant costs have skyrocketed — it may be time to replace the unit.

Learn more: Signs of a Refrigerant Leak

Frozen Evaporator Coil

If you see ice on the indoor coil or refrigerant lines, your coil is frozen. Common causes:

• Dirty air filter (see #1 above)
• Low refrigerant
• Blocked return vents (don’t close vents in unused rooms — it causes pressure problems)
• Malfunctioning blower fan

What to do: Turn the system OFF but keep the fan running on “ON” to defrost. This can take 1-4 hours. If it freezes again after thawing, call a technician.

Dirty Condenser Coils

The outdoor unit’s coils release heat from your home into the outside air. When they’re coated in dirt, pollen, or grass clippings (very common in the Upstate), the system can’t dump heat efficiently.

DIY fix: Gently spray the outdoor coils with a garden hose (no pressure washer!). Spray from the inside out. This is also a great maintenance task to do monthly during cooling season.

Failed Compressor

The compressor is the most expensive component in your AC. When it fails:

• The outdoor fan may run, but the compressor won’t cycle
• Air from vents feels room-temperature, not warm or cool
• You may hear clicking or unusual sounds from the outdoor unit

Cost: $2,500-$4,500 for replacement. If your system is over 10 years old, it often makes more sense to replace the entire system rather than just the compressor.

Learn more: How Long Should My HVAC System Last?

Bad Capacitor

Capacitors are small electrical components that help start and run the compressor and fan motors. They’re one of the most common AC failures, especially in hot climates like South Carolina.

Signs: AC tries to start but doesn’t, humming sound from outdoor unit, intermittent cooling.

Cost: $150-$400 for replacement. This is a relatively inexpensive fix.

Ductwork Leaks

If your ductwork has gaps, cracks, or disconnected sections (common in crawl spaces and attics), cool air leaks into unconditioned space before reaching your rooms.

In the Upstate, we routinely find homes losing 20-30% of their cooled air through duct leaks. Your AC is cooling just fine — it’s just cooling your attic instead of your living room.

Why Is My AC Blowing Warm Air Specifically?

If the air coming from your vents is actively warm (not just room-temperature):

• Thermostat set to heat mode (check first!)
• Reversing valve stuck (heat pump systems) — the system is in heating mode when it should be cooling
• Compressor failure — the refrigerant isn’t cycling

When to Call a Professional

Call an HVAC technician when:

• You’ve checked the filter, thermostat, breakers, and outdoor unit — and it’s still not cooling
• You see ice on any part of the system
• The outdoor unit isn’t running at all
• The system is making unusual noises (grinding, screeching, banging)
• Your electric bill has spiked without explanation
• The system short cycles (turns on and off every few minutes)

How to Prevent This From Happening Again

• Change your filter regularly. Set a phone reminder. This is the single most impactful thing you can do.
• Schedule spring maintenance. A tune-up before summer catches issues when they’re cheap to fix.
• Keep the outdoor unit clear. 2 feet of clearance, no bushes or debris.
• Don’t close vents in unused rooms. Your system is sized for the whole house.
• Consider a maintenance plan. Our Club Wally membership includes two tune-ups per year, priority scheduling, and discounts on repairs.

How Waldrop Can Help

At Waldrop Plumbing Air Electric, our NATE-certified HVAC technicians diagnose AC problems every day. We’ll tell you what’s wrong, what it’ll cost to fix, and whether repair or replacement makes more financial sense. No pressure, no upselling — just honest answers.

If your AC isn’t cooling and you’ve tried the steps above, call us at (864) 536-0887 or schedule online — we offer same-day service for most AC repairs in Greenville, Spartanburg, and the surrounding Upstate area.

Frequently Asked Questions

Why is my AC running but not cooling my house?
The most common cause is a dirty air filter restricting airflow. Other causes include low refrigerant, frozen evaporator coils, dirty condenser coils, a failed compressor, or ductwork leaks.

How can I tell if my AC is low on refrigerant?
Signs include lukewarm air from vents, ice forming on refrigerant lines or the evaporator coil, hissing or bubbling sounds, and higher electric bills.

What should I do if my AC coil is frozen?
Turn the system OFF but keep the fan running on “ON” to defrost the coil. This can take 1-4 hours. If it freezes again after thawing, call a technician.

How much does it cost to fix an AC that’s not cooling?
It depends on the cause. Filter replacement is free (if you do it yourself). Capacitor replacement costs $150-$400. Refrigerant leak repair costs $200-$1,500. Compressor replacement costs $2,500-$4,500.

Can I fix my AC myself if it’s not cooling?
You can check and replace the air filter, verify thermostat settings, check circuit breakers, and clean debris from the outdoor unit. Beyond that, you’ll need a licensed HVAC technician.

How often should I change my AC filter?
Standard 1-inch filters should be changed every 30-60 days during cooling season in South Carolina. If you have pets, change it every 30 days.