When your AC is running but not cooling, it's frustrating—especially in the Texas heat. This guide walks you through 12 common causes, which ones you can fix yourself, and when it's time to call a professional.
A dirty or clogged air filter is the #1 reason ACs stop blowing cold air. It restricts airflow, causing the evaporator coil to freeze. Replace your filter, turn off the AC for 2-4 hours to let any ice thaw, then restart. If that doesn't work, keep reading.
Before you call for service, run through these checks—you might solve the problem in 5 minutes:
If you checked all of these and the AC still isn't cooling, one of the causes below is likely the culprit.
Here's every common cause, organized from easy DIY fixes to problems that need professional repair:
Symptoms: Weak airflow, warm air, ice on indoor unit
Why it happens: A clogged filter blocks airflow over the evaporator coil. Without enough air, the coil gets too cold and freezes. Ice insulates the coil, preventing it from absorbing heat.
Fix: Replace the filter. If there's ice, turn off the AC (leave fan on AUTO) for 2-4 hours until ice melts completely, then restart.
Symptoms: AC doesn't turn on, runs at wrong times, or blows room-temp air
Why it happens: Dead batteries, wrong settings, or the thermostat isn't communicating with the AC properly.
Fix: Replace batteries, verify settings (COOL mode, fan on AUTO, temp set below room temp). If it's a programmable thermostat, check the schedule.
Symptoms: Fan blows but air isn't cold (indoor breaker on, outdoor breaker tripped)
Why it happens: Your AC has two breakers—one for the indoor air handler, one for the outdoor condenser. If only the outdoor breaker trips, the fan runs but the compressor doesn't.
Fix: Reset both breakers. If it trips again immediately, there's an electrical problem—call a technician.
If your AC breaker trips repeatedly, don't keep resetting it. This indicates an electrical fault that could damage equipment or create a fire hazard. Call for professional service.
Symptoms: Some rooms cool, others don't; system struggles to reach set temperature
Why it happens: Closed supply vents, furniture blocking returns, or ducts disconnected in the attic.
Fix: Open all vents and registers. Ensure furniture isn't blocking return air grilles. Check accessible ductwork for obvious disconnections.
Symptoms: AC runs but doesn't cool well; may cycle on and off frequently
Why it happens: The condenser releases heat from your home. If it's covered in dirt, leaves, or debris, it can't release heat effectively.
Fix: Turn off the AC. Gently rinse the condenser coils with a garden hose (from inside out). Remove any debris. Maintain 2 feet of clearance around the unit.
Symptoms: Ice visible on indoor unit or refrigerant lines, weak or warm airflow
Why it happens: Dirty filter, low refrigerant, or blower motor problems cause the coil to freeze. Once frozen, it can't absorb heat.
Fix: Turn off AC, let ice thaw completely (2-4 hours), replace filter. If it freezes again, you have low refrigerant or an airflow problem—call a technician.
Symptoms: AC shuts off unexpectedly, water around indoor unit, musty smell
Why it happens: The drain line removes moisture from your home. When clogged with algae or debris, water backs up. Many systems have a float switch that shuts off the AC when this happens.
Fix: Locate the drain line (usually PVC pipe near indoor unit). Try clearing it with a wet/dry vacuum or flushing with vinegar. If unsuccessful, call for service.
Symptoms: Gradual loss of cooling capacity over time, higher energy bills
Why it happens: Dust and debris bypass the filter and accumulate on the evaporator coil, insulating it and reducing heat absorption.
Fix: This requires professional cleaning. The evaporator coil is inside the air handler and needs careful handling to avoid damage. Include this in annual AC maintenance.
Symptoms: Warm air, ice on refrigerant lines, hissing sound, AC runs constantly without cooling
Why it happens: Refrigerant doesn't "run out"—if it's low, there's a leak somewhere in the system.
Fix: Requires professional diagnosis. A technician will find the leak, repair it, and recharge the system. Simply adding refrigerant without fixing the leak is a temporary (and expensive) bandage. See AC repair costs →
Symptoms: Outdoor unit hums but doesn't start, or doesn't run at all; no cooling
Why it happens: The compressor is the "heart" of the AC. It fails due to age, electrical problems, lack of maintenance, or running with low refrigerant.
Fix: Compressor replacement costs $1,200-$2,500. If your AC is over 10 years old, replacement may be more cost-effective than repair.
Symptoms: AC doesn't start, makes clicking or humming sound, outdoor fan doesn't spin
Why it happens: Capacitors store energy to start the compressor and fan motors. They fail due to age, heat damage, or power surges.
Fix: Capacitor replacement is a common, affordable repair ($150-$300). However, capacitors store dangerous electrical charge—this is not a DIY repair.
Symptoms: Some rooms won't cool, AC runs constantly, high energy bills
Why it happens: Leaky ducts in the attic lose cooled air before it reaches your rooms. Disconnected or crushed ducts block airflow entirely.
Fix: Duct inspection and sealing requires professional assessment. In Dallas-Fort Worth, attic temperatures reach 140°F+, so duct leaks are extremely costly.
Here's exactly how to handle the DIY-friendly issues:
Never use a pressure washer on your condenser coils—it bends the delicate aluminum fins and damages the unit. A regular garden hose with moderate pressure is all you need.
Call an HVAC technician if:
Professional diagnosis costs $75-$150 (often waived if you proceed with repairs) and ensures you fix the right problem the first time. Learn more about what AC repairs cost.
LEX Air offers emergency AC repair with technicians arriving in 25-35 minutes. Call (972) 466-1917.
Most AC failures are preventable with basic maintenance:
Our Cool Club maintenance plan includes 2 tune-ups per year, 15% off repairs, priority scheduling, and no overtime charges. Members rarely experience unexpected breakdowns because we catch problems early.
The most common causes are a dirty air filter restricting airflow, low refrigerant due to a leak, a frozen evaporator coil, or a malfunctioning compressor. First, check and replace your air filter, then inspect the outdoor unit to ensure it's running. If the problem persists, call an HVAC technician.
Sudden warm air often indicates a refrigerant leak, a tripped circuit breaker to the outdoor unit (so only the fan runs indoors), or a failed compressor. Check your thermostat settings first—someone may have accidentally switched it to heat mode. Then check your circuit breaker panel for tripped breakers.
Absolutely. A severely clogged filter restricts airflow over the evaporator coil, causing it to freeze solid. A frozen coil can't absorb heat from your home, so your AC blows room-temperature or warm air. This is the #1 cause of AC cooling problems and is easily preventable.
Signs of low refrigerant include: warm air from vents even when the AC is running, ice buildup on the refrigerant line or evaporator coil, hissing or bubbling sounds (indicating a leak), higher than normal electric bills, and the AC running constantly without ever reaching the set temperature.
Yes, especially if you notice ice on the unit or if the outdoor unit isn't running. Running an AC with a frozen coil or failed compressor can cause additional damage. Turn the system off, let any ice thaw for 2-4 hours, then call for service.
This suggests your AC is undersized or struggling with extreme heat. During the hottest part of the day, the system can't remove heat fast enough. It might also indicate dirty coils, low refrigerant, or duct leaks that become more apparent under heavy load. Have a technician assess your system's capacity.
If quick checks (filter, thermostat, breakers) don't solve the problem, call for service. In Texas summer heat, waiting allows your home to heat up significantly, making the AC work harder to recover once fixed. Most repairs can be completed same-day if you call early.
Our NATE-certified technicians arrive in 25-35 minutes with the parts and expertise to fix your AC today.
