When things go wrong

Your AC isn't cooling — basic troubleshooting before you call

Staff

01 May 2025 — 3 min read

This article is for educational purposes only and is not a substitute for professional advice. Local codes, regulations, and best practices vary by region.

Your air conditioner isn’t cooling. It’s running but the house is hot. You’re uncomfortable and you’re wondering if you need to call an HVAC technician right now or whether you can check a few things first. There are some basic checks that might reveal a simple problem. Sometimes you’ll save yourself a service call. At minimum, you’ll have useful information when you do call.

AC not cooling has several possible causes. Some are simple fixes. Some require professional repair. Starting with basic checks helps identify which category you’re in.

Check the Thermostat

Verify the thermostat is set to cool mode. If it’s set to heat or off, cooling won’t run. Set it to cool and a temperature below the current room temperature. The unit should start.

Check the thermostat batteries (if it has them). Low batteries prevent it from functioning. Replace them and test again.

Some thermostats have a delay when switching between modes. If you just switched from heat to cool, wait 5 minutes for the system to start.

Check Air Filter

A clogged air filter restricts airflow and reduces cooling capacity. Check the filter. If it’s visibly dirty, replace it. A dirty filter can make a functioning AC perform poorly.

Filters are inexpensive ($10-20) and simple to replace. Locate your air handler, remove the old filter, insert the new one. This single step might restore cooling.

Check the Outdoor Unit

Look at the outdoor AC condenser unit. Is it running? You should hear and see the fan running. If it’s not running, the system isn’t operating. If the breaker to the unit has tripped, reset it.

Is the unit surrounded by debris, leaves, or dirt? Clear it away. Restricted airflow prevents proper cooling.

Is ice accumulating on the coils? This can prevent cooling and suggests a deeper problem. This requires professional attention.

Listen and Feel

Does the system produce cold air at the vents? Feel the air coming out. It should be noticeably cold. If air is warm, the system isn’t cooling properly.

Are you hearing unusual sounds (grinding, squealing, hissing)? These suggest mechanical or refrigerant problems requiring professional repair.

Check Air Vents and Ducts

Are vents open and unobstructed? Closed vents or blocked ducts reduce cooling in specific areas. Open all vents.

Is the return air vent (where air gets pulled into the system) clogged with dust or debris? Clean it. Restricted return air reduces system efficiency.

Basic Troubleshooting Summary

If the thermostat is set correctly, filter is clean, outdoor unit is running, cold air is coming from vents, and nothing sounds wrong, the system is functioning but might be undersized for the heat load. This is not an emergency but should be evaluated.

If the thermostat isn’t responding, the unit won’t start, there’s ice on the outdoor unit, or air is warm, professional help is needed.

Common AC Problems Requiring Service

Refrigerant leak: The system gradually loses refrigerant. Cooling capacity decreases. Eventually, it stops cooling. Professional repair and refrigerant recharge are needed. Cost is $300-800.

Compressor failure: The compressor (the heart of the system) fails. The system won’t cool. Replacement is expensive ($1,500-3,000+). At this point, replace-vs-repair decision is necessary.

Condenser fan failure: The outdoor fan stops working. The unit can’t reject heat. Cooling performance drops. Fan replacement costs $500-1,000.

Blower motor failure: The indoor fan stops working. Even if the system cools, air isn’t distributed. Blower replacement costs $500-1,500.

When to Call an Hvac Technician

Call if the unit won’t start after checking thermostat and breaker. Call if air is warm despite the system running. Call if you hear unusual sounds. Call if ice is forming. Call if the unit isn’t cooling even with filter replaced and outdoor unit clear.

HVAC service calls cost $150-300 for diagnosis. Repairs vary widely depending on the problem. AC maintenance (cleaning, refrigerant check) costs $100-200 annually.

Temporary Coping

While waiting for service, use fans to circulate air. Close blinds to reduce solar heat gain. Use dehumidifiers if humidity is extreme.

These are temporary measures, not solutions.

Prevention

Regular maintenance prevents many AC failures. Annual cleaning and inspection catch problems early. Filters changed quarterly extend system life. Keeping the outdoor unit clear prevents debris damage.

The Bottom Line

AC not cooling might be thermostat, filter, or power issue. Check these first. If these simple checks don’t restore cooling, the system needs professional service. Don’t ignore AC failure during hot weather. Call an HVAC technician if your troubleshooting doesn’t solve the problem. Most AC failures require professional repair, but basic checks sometimes reveal simple fixes.