What if my AC is running but not cooling?
The unit may be on and blowing air, but you’re not getting the cool air you expect. In many cases the cause is a simple airflow or thermostat issue, while refrigerant leaks or a failing compressor require professional intervention. Here’s how to understand and address the problem.
Common causes of an AC that runs but won’t cool
Breakdowns fall into a few broad categories. Understanding where the problem likely sits helps you decide what to fix yourself and what to leave to a pro.
Airflow and filtration problems
Blocked or restricted airflow can prevent the evaporator from removing heat, making the space feel warm even with the unit running.
- Dirty or clogged air filters reducing airflow.
- Blocked or closed vents in rooms or ducts with restricted airflow.
- Malfunctioning blower motor or fan in the indoor air handler.
Clearing obstructions, replacing dirty filters, and addressing duct issues often restore cooling performance. If ducts are severely leaky or damaged, a professional assessment is advised.
Refrigerant and cooling cycle problems
Without sufficient refrigerant or a faulty cooling cycle, the evaporator coil can’t absorb heat properly, leading to warm air.
- Low refrigerant due to leaks or improper charging.
- Faulty metering device, expansion valve, or other refrigerant-control components.
- Ice buildup on the evaporator coil indicating airflow or refrigerant problems.
A refrigerant issue is not a DIY fix; handling refrigerant requires EPA-certified professionals and can require leak repair before recharging.
Mechanical and electrical issues
Even when air is flowing, the outdoor compressor or other electrical components may fail to deliver cooling.
- Faulty compressor or failing start capacitor/relay.
- Tripped breaker, blown fuse, or a failed contactor in the outdoor unit.
- Thermostat or sensor problems causing incorrect cooling signals.
- Age-related wear or component damage in older systems.
Electrical or mechanical problems can pose safety risks; if you suspect a fault with power or wiring, contact a pro promptly.
What homeowners can safely check now
Before calling a technician, you can perform a few safe, noninvasive checks to narrow down the issue. Always shut off power at the breaker before inspecting equipment.
Thermostat and power checks
Configuration and power issues are common culprits that homeowners can verify quickly.
- Confirm the thermostat is set to cool and the target temperature is lower than room temperature.
- Check that the thermostat display is active; replace batteries or reprogram if needed.
- Ensure the outdoor disconnect switch is on and the indoor blower is operating.
Adjusting the thermostat and confirming power may resolve simple misconfigurations that mimic a non-cooling problem.
Air filter and duct checks
Airflow begins with clean filtration and clear pathways for air to move through the system.
- Replace disposable filters and keep the air return and supply vents unobstructed.
- Inspect the outdoor unit for leaves, debris, snow, or other obstructions; clear around the condenser.
- Check for obvious signs of duct damage or loose connections that could reduce airflow.
Improving airflow often yields noticeable cooling gains without professional work.
Basic power and outdoor unit checks
Power supply and outdoor unit condition influence whether cooling actually occurs.
- Listen for a hum from the outdoor unit indicating the compressor is trying to start; if nothing runs, check the circuit breaker or fuse.
- Reset a tripped breaker and see if the outdoor unit starts functioning.
- Look for ice on refrigerant lines or the evaporator coil; persistent icing requires professional diagnosis.
If these checks don’t restore cooling, the issue may be refrigerant, compressor, or other components that require expert service.
When to call a professional
Some issues demand licensed HVAC technicians due to safety, refrigerant handling, and the complexity of modern systems. If you notice any of the following, contact a pro promptly.
- You suspect a refrigerant leak (hissing sounds, oily residue on lines, or persistent icing) or the system cannot be charged correctly.
- Ice persists on the evaporator coil or refrigerant lines even after basic checks and de-icing, indicating deeper airflow or refrigerant problems.
- Unusual noises, burning odors, or visible electrical arcing coming from the outdoor unit or controls.
- The thermostat seems to be functioning, but the system fails to reach or hold the set temperature consistently.
- The unit is older (roughly 10–15 years or more) with reduced efficiency and ongoing cooling problems, suggesting replacement vs. repair.
Note: Handling refrigerants requires EPA certification. Technicians will diagnose, repair leaks, evacuate and recharge refrigerant as needed, and verify system performance after service.
Preventive maintenance tips
Regular upkeep reduces the likelihood of running-but-not-cooling scenarios and extends the life of your system.
- Replace filters every 1–3 months, or more often in dusty environments or with pets.
- Schedule annual professional inspections for coil cleaning, refrigerant checks, and overall system performance.
- Keep the outdoor unit clear of leaves, debris, and vegetation; provide at least 2–3 feet of clearance for proper airflow.
- Inspect insulation on refrigerant lines and seal any duct leaks to maintain efficiency.
- Use a programmable thermostat to optimize cooling and energy use.
Proactive maintenance is the best defense against future episodes of “running but not cooling.”
Summary
When an air conditioner runs but fails to cool, the root cause typically lies in airflow, refrigerant issues, or a failing component. Start with safe, basic checks—thermostat settings, filters, vents, and power—before consulting a professional, especially if you suspect a refrigerant leak or electrical problem. Regular maintenance remains the strongest defense against this frustrating issue and helps extend system life.
