Why is my AC turning on but no airflow?
The indoor blower is not delivering air even though the outdoor unit is running. Most often this points to issues inside the air handler or furnace, such as a faulty blower, a tripped safety switch, a clogged filter, or a thermostat/control problem. Quick checks can reveal whether it’s a simple fix or a sign of a larger repair.
Air conditioning relies on two halves: the outdoor condenser that cools refrigerant and the indoor air handler or furnace that moves air through the ducts. When the compressor runs but you feel no airflow from the vents, the fault usually lies with the indoor blower, an interlock or safety switch, or an obstructed air path. The following guide covers common causes and practical steps to diagnose and address them.
Common causes and fixes
Below are the main categories of causes, followed by practical checks you can perform. The list focuses on indoor-unit issues, electrical/control problems, and air-path troubles.
Indoor-side issues
These problems occur inside the air handler or furnace and directly affect the blower’s ability to push air through the ducts.
- Dirty or blocked air filter restricting airflow or triggering a system shutdown.
- Thermostat or fan settings that prevent the indoor blower from running.
- Indoors blower motor or capacitor failure, stopping the blower even when the outdoor unit runs.
- Tripped safety switch or blown fuse on the indoor unit, cutting power to the blower.
- Blower relay or control board fault, failing to energize the fan.
- Condensate overflow switch engaged due to a clogged drain, shutting down the system for safety.
If you suspect any of these indoor issues, start with the simplest checks and avoid handling electrical components if you’re not trained.
Electrical and control issues
Power delivery or control signaling problems can keep the blower idle even when the outdoor unit appears to operate.
- Blown fuse or tripped circuit breaker to the indoor unit.
- Damaged wiring, loose connections, or a faulty control board that fails to energize the blower.
- Worn or collapsed capacitor in the blower motor (a common failure that stops the fan).
Electrical problems can pose shock or fire risks. If you see sparking, burning smells, or signs of overheating, shut off power at the breaker and contact a professional.
Airflow and ductwork
Even when the blower runs, blocked ducts or closed dampers can prevent air from reaching rooms.
- Closed or blocked supply registers and dampers restricting airflow to living spaces.
- Blocked or collapsed ducts, especially in attics or crawl spaces, reducing or stopping airflow.
- Leaks in ductwork causing loss of pressure and weak or no airflow.
Thorough duct inspection and repair often require professional assessment and equipment, especially for hidden or collapsed sections.
What to do next
If basic checks don’t restore airflow, contact a licensed HVAC technician. They can safely test electrical components, verify blower motor operation and capacitor health, inspect the control board, and evaluate duct integrity. Early diagnosis can prevent further damage and ensure safe, efficient cooling.
Safety notes and when to call a pro
Do not bypass safety switches or attempt complex electrical work if you’re not trained. If you smell burning, hear buzzing, or notice signs of overheating, shut off power at the breaker and call a professional immediately. HVAC systems can involve high voltage, moving parts, and refrigerant that require specialized tools and training.
Summary
When your AC turns on but you get no airflow, the culprit is usually on the indoor side: the blower, safety interlocks, or the air pathway. Start with simple steps like replacing a dirty filter, confirming thermostat and fan settings, and ensuring safety switches are engaged. If airflow remains absent, seek professional diagnosis to address blower motor or capacitor issues, electrical/control faults, or duct problems and restore proper cooling.
