AC Not Cooling? 12 Causes & Fixes

When your AC stops cooling in the middle of a Central Texas summer, it's more than uncomfortable — it can be dangerous with temperatures exceeding 100°F. Before you call for service, there are several things you can check yourself. This guide covers the 12 most common reasons your AC isn't cooling and what to do about each one.

Quick DIY Checklist (Try These First)

Before calling a technician, check these 5 things that take less than 5 minutes and fix the problem about 30% of the time:

12 Common Reasons Your AC Is Not Cooling

1. Dirty or Clogged Air Filter

How common: Very common — causes about 25% of AC cooling problems.
Symptoms: Weak airflow, AC runs constantly, ice on indoor coil, warm air from vents.

A clogged filter restricts airflow across the evaporator coil. Without enough air, the coil drops below freezing and ice builds up, blocking airflow completely. The AC runs but produces little or no cooling.

Fix: Replace the filter. In Central Texas, replace every 30-60 days during summer due to high dust and pollen. Use our Filter Size Finder to find the right replacement. Cost: $5-$25.

2. Thermostat Issues

How common: Common — about 10% of service calls.
Symptoms: AC doesn't turn on, runs at wrong times, wrong temperature reading.

Sometimes the fix is as simple as dead batteries, the mode being set to HEAT or FAN ONLY, or the set temperature being above room temperature. Smart thermostats can also lose Wi-Fi connection and revert to default schedules.

Fix: Replace batteries, verify COOL mode, set temperature 3-5°F below room temp. If the display is blank even with fresh batteries, the thermostat may need replacement ($150-$350 installed).

3. Low Refrigerant (Refrigerant Leak)

How common: Very common — about 20% of cooling failures.
Symptoms: Warm air from vents, hissing/bubbling sounds, ice on refrigerant lines, higher electric bills.

AC systems don't "use up" refrigerant — if it's low, there's a leak. Low refrigerant means the evaporator coil can't absorb enough heat, so the air coming from your vents is warm. The system works harder and harder but can't reach the set temperature.

Fix: Professional only. A technician must find and repair the leak, then recharge the system. Cost: $150-$400 for a recharge, $200-$1,500 if the leak requires a coil repair. Check current refrigerant costs for your system type.

4. Frozen Evaporator Coil

How common: Common, especially in summer.
Symptoms: Ice visible on indoor unit or refrigerant lines, water leaking when ice melts, warm air from vents.

A frozen coil is usually a symptom of another problem: dirty filter, low refrigerant, failed blower motor, or dirty coil. The coil freezes because it's not getting enough heat transfer from airflow.

Fix: Turn the AC off and set the fan to ON for 2-3 hours to thaw. Replace the filter if dirty. If it refreezes, call a technician — you likely have a refrigerant leak or blower motor issue.

5. Dirty Condenser Coil (Outdoor Unit)

How common: Common in Central Texas due to dust, cottonwood, and grass clippings.
Symptoms: AC cools poorly in afternoon heat, compressor overheats and shuts off, high electric bills.

The outdoor condenser coil releases heat from your home into the outside air. When it's coated in dirt, grass, or debris, it can't release heat efficiently. On hot days, this causes the compressor to overheat and shut down on a safety switch.

Fix: Turn off the AC. Gently spray the outdoor coil fins with a garden hose (not a pressure washer) from the inside out. Clear all vegetation at least 2 feet from the unit. Cost: Free (DIY). For heavy buildup, a professional coil cleaning costs $75-$200.

6. Failed Capacitor

How common: Very common in Texas — heat kills capacitors.
Symptoms: AC hums but won't start, fan doesn't spin, clicking sounds, intermittent cooling.

Capacitors are like batteries that give the compressor and fan motors the jolt of energy needed to start. Texas heat degrades capacitors faster than in cooler climates. A failing capacitor causes the compressor to struggle to start — it might work sometimes but fail in peak afternoon heat.

Fix: Professional only — capacitors store lethal voltage even when the power is off. Cost: $150-$300 for the part and labor. This is one of the most common and affordable AC repairs.

7. Compressor Failure

How common: Less common but serious.
Symptoms: Outdoor unit fan runs but compressor is silent, tripped breaker, warm air only.

The compressor is the heart of your AC system — it pressurizes refrigerant and circulates it through the system. When it fails, the AC produces zero cooling. Compressor failure is often caused by running with low refrigerant, electrical issues, or age (typically 10-15+ years).

Fix: Professional only. A new compressor costs $1,200-$2,500 installed. However, if the system is over 10 years old, replacing the entire system is often more cost-effective. Use our Cost Estimator to compare options.

8. Tripped Circuit Breaker

How common: Common, especially after power outages.
Symptoms: AC completely off, no response from thermostat or outdoor unit.

Your AC has two breakers — one for the indoor air handler/furnace and one for the outdoor condenser. Power surges, storms, or a momentary overload can trip either one. Check your electrical panel.

Fix: Reset the breaker by flipping it fully OFF then back ON. If it trips again within an hour, do NOT keep resetting it — there's an electrical fault that needs professional diagnosis. Repeated trips can indicate a short circuit, grounding issue, or failing compressor.

9. Clogged Condensate Drain

How common: Very common in humid climates like Central Texas.
Symptoms: AC shuts off unexpectedly, water pooling around indoor unit, musty smell.

Your AC removes moisture from the air — up to 20 gallons per day in humid conditions. This water drains through a PVC pipe. When the drain clogs (with algae, mold, or debris), a safety float switch shuts off the AC to prevent water damage.

Fix: Locate the drain line (usually a PVC pipe near your indoor unit). Pour a cup of white vinegar or bleach into the drain access point to clear algae. If the clog is severe, use a wet/dry vacuum on the outdoor end of the drain. Do this monthly during summer. Cost: Free (DIY).

10. Duct Leaks or Disconnected Ductwork

How common: More common than people realize — typical homes lose 20-30% of cooled air through duct leaks.
Symptoms: Some rooms cool fine but others don't, high energy bills, dusty house, AC runs constantly.

Leaky ducts dump cooled air into your attic or crawl space instead of into your rooms. In a Central Texas attic that reaches 140°F+, duct leaks are extremely costly. Disconnected flex ducts are also common after storms, pest activity, or poor installation.

Fix: Visually inspect accessible ductwork in the attic for obvious disconnections or damage. Professional duct sealing costs $300-$1,500 but can reduce cooling costs by 20-30%.

11. Undersized AC System

How common: Fairly common, especially in older homes that have been renovated.
Symptoms: AC runs all day without reaching set temperature, struggles on hot afternoons, high bills.

If your AC was sized for a smaller home, or if you've added square footage, insulation has degraded, or you've added more windows, the system may simply not have enough capacity. Central Texas homes typically need 1 ton of cooling per 500-600 square feet.

Fix: Use our BTU Calculator to determine the right size for your home. If undersized, the only solution is replacing the system with a properly sized unit. Check installation costs for your area.

12. Old or Worn-Out System

How common: AC systems last 15-20 years in moderate climates, but only 10-15 years in Central Texas.
Symptoms: Frequent repairs, rising energy bills, uneven cooling, R-22 refrigerant system.

After 12-15 years in the Texas heat, AC systems lose efficiency and become prone to multiple failures. If your system uses R-22 refrigerant (Freon), recharges now cost $100-$175 per pound because it's been phased out. At that point, replacement is almost always the better investment. Read our When to Replace Your AC Unit guide for a detailed cost comparison and the 8 warning signs it's time.

Fix: Use our HVAC Age Decoder to find your system's exact age from the serial number. Then use the Repair or Replace Calculator to see if replacement makes financial sense.

When to Call a Professional

Call an HVAC technician if:

• You've replaced the filter and checked the thermostat but still have no cooling
• The outdoor unit is running but the compressor isn't engaging
• There's ice on the refrigerant lines or indoor coil
• You hear unusual sounds (grinding, screeching, banging)
• The breaker trips repeatedly
• You smell burning or electrical odors
• The system is over 10 years old and needs frequent repairs

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