AC Not Blowing Cold Air: Causes and Repair Cost

Check Before You Call a Technician

Before spending $75 to $150 on a service call, check these things yourself. First, verify that the thermostat is set to "cool" and the temperature is set below the current room temperature. This sounds obvious, but thermostat settings get bumped accidentally, and it accounts for a surprising number of service calls. Also check that the fan setting is on "auto" rather than "on," because the "on" setting runs the blower continuously even when the compressor is off, pushing unconditioned air through the vents and making it feel like the system is not cooling.

Second, check your air filter. A severely clogged filter restricts airflow across the evaporator coil so much that the coil cannot absorb heat effectively, resulting in warm air from the vents. If the filter is visibly dirty, replace it ($5 to $30), give the system 30 to 60 minutes to recover, and see if cold air returns. If the filter was severely clogged, the evaporator coil may have frozen over, in which case you need to run the system in "fan only" mode for one to four hours to let the ice melt before trying cooling mode again.

Third, check the outdoor unit. The condenser needs clear airflow to release heat. If vegetation, debris, or a damaged fence panel is blocking the unit, clearing a two-foot perimeter around it may solve the problem. Also verify that the outdoor fan is spinning. If the unit is silent or only humming, move on to the electrical checks below. Fourth, check your circuit breaker panel. The indoor and outdoor units are on separate breakers, and if the outdoor breaker has tripped, the indoor fan will blow air through the vents but the compressor will not run, so the air will be warm. Reset the breaker once, but if it trips again immediately, do not reset it a second time because this indicates a short circuit or ground fault that requires professional repair.

Low Refrigerant: $200 to $1,500

Low refrigerant is the most common cause of warm air from an AC that is otherwise running normally. Refrigerant does not get "used up" during normal operation, so a low charge always means there is a leak somewhere in the system. The repair involves finding the leak, sealing it, and recharging the system with the correct amount of refrigerant.

A simple recharge without major leak repair runs $200 to $500. When the leak is in a brazed joint, valve, or service port, finding and repairing it before recharging adds $300 to $1,000 to the total. R-410A refrigerant now costs $50 to $90 per pound installed, and a typical system needs 6 to 16 pounds for a full charge. Our refrigerant recharge cost guide has current pricing details and explains how the R-410A phase-down is affecting costs.

You can sometimes identify low refrigerant before calling a technician. Check the larger copper line (the suction line) running from the outdoor unit to the wall of your house. During normal operation, this line should be cold and sweating with condensation. If it is warm or dry, the system is likely low on refrigerant. If you see frost or ice forming on this line, the refrigerant is critically low and the coil is probably frozen.

Dirty or Frozen Evaporator Coil: $100 to $1,500

The evaporator coil is the indoor component that absorbs heat from your home's air. When it gets coated with dust and grime (typically from running without a filter or with a very old filter), its heat absorption drops and the air coming out of the vents feels barely cool. Professional coil cleaning costs $100 to $400 and should be part of your annual maintenance.

If the coil has frozen over, you will see ice buildup on the copper lines near the indoor unit, and the system will blow room-temperature air. Common causes include restricted airflow (dirty filter, closed vents), low refrigerant, or a failing blower motor. Turn the system off and let the ice melt completely before having a technician diagnose the underlying cause. Do not try to chip or scrape ice from the coil, as the fins and tubing are delicate and easily damaged. See our full guide on why your AC freezes up for all the causes and their repair costs.

Failed Capacitor: $150 to $400

If the outdoor unit hums but the fan is not spinning, or if the fan starts slowly and then struggles, a failed capacitor is the likely cause. Without a working capacitor, the compressor may not start at all, which means no cooling. This is one of the cheapest and most common AC repairs, with the full replacement (part plus labor) running $150 to $400. The repair usually takes 15 to 30 minutes.

A weak capacitor can also cause partial symptoms where the system starts and runs but produces noticeably less cooling than normal. The compressor runs at reduced efficiency because it is not receiving the full electrical boost it needs, drawing more power and producing less cooling. If your system seems to cool the house but takes much longer than usual, a weakening capacitor may be the cause.

Compressor Failure: $800 to $2,800

When the compressor fails, the system cannot circulate refrigerant at all, and the air from your vents will be room temperature or slightly warm. Compressor failure often presents as the outdoor unit running but making unusual noises (clicking, buzzing, or rattling) or the unit tripping the breaker repeatedly. In some cases, the outdoor unit will not start at all and may only hum briefly before the safety overload shuts it down.

Compressor replacement is the most expensive AC repair at $800 to $2,800. For systems older than 10 years, most HVAC professionals recommend replacing the entire system rather than investing in a new compressor for aging equipment because other components are likely approaching the end of their service life as well. Before authorizing a compressor replacement, have the technician verify the diagnosis by testing the capacitor and contactor first, since these cheaper components can mimic compressor failure symptoms.

Condenser Fan Motor Failure: $200 to $700

The condenser fan draws air across the outdoor coil to release heat. If this fan stops working, the system overheats and either blows warm air or shuts down on a high-pressure safety switch. You can often diagnose this by listening to the outdoor unit. If you hear the compressor running (a steady electrical hum or vibration) but the fan is not spinning, the fan motor has likely failed.

In some cases, a failed fan motor allows the compressor to run long enough to superheat the condenser coil, which means the system cannot reject heat and the indoor air stays warm. If you catch a stopped condenser fan early and turn the system off, you prevent the compressor from overheating and potentially suffering damage. Replacement costs $200 to $700 depending on the motor type and brand.

Thermostat or Wiring Issues: $100 to $500

A malfunctioning thermostat can send incorrect signals to the system, causing it to run the fan without activating the compressor. Wiring problems between the thermostat and the air handler or outdoor unit can produce the same symptom. Thermostat replacement costs $100 to $300, while wiring repairs run $150 to $500 depending on the complexity and accessibility of the wiring. If your thermostat display is working and showing correct readings but the system is not responding to temperature changes, the issue may be in the wiring between the thermostat and the equipment rather than the thermostat itself.

Ductwork Leaks: $200 to $1,000

If your AC is producing cold air at the unit but the air coming from the vents is barely cool, the ductwork may be leaking conditioned air into the attic, crawl space, or walls. Duct systems can lose 20 to 30 percent of airflow through leaks, disconnected joints, and poor insulation. This is especially common in older homes where duct connections have loosened over time or in homes where the ductwork runs through unconditioned spaces like attics where the temperature can exceed 140 degrees in summer.

Professional duct sealing costs $200 to $1,000 depending on the extent of the leaks and how accessible the ductwork is. The technician uses mastic sealant or metal tape (not standard cloth duct tape, which fails within a few years) to seal joints and connections. In some cases, adding duct insulation in unconditioned spaces is necessary to prevent the already-cooled air from absorbing heat as it travels through hot attic spaces to the registers.