AC Not Cooling? 12 Common Causes and What Each Fix Costs

Your air conditioner is running but your house isn't getting cooler. Before you panic-call an HVAC contractor at emergency rates, understand that 70% of AC cooling failures fall into just 12 categories — and four of them you can diagnose and fix yourself in under 30 minutes. This guide ranks every common cause by frequency, explains what's happening inside your system, and tells you exactly what the repair will cost.

Run through these four checks first. They resolve roughly 30% of "AC not cooling" calls and cost you nothing:

The single most common reason your AC stops cooling effectively. A clogged filter restricts airflow across the evaporator coil, causing the coil to drop below 32°F and freeze over. Once frozen, the system can't absorb heat from your home's air. Fix: Turn off the AC, let the coil thaw for 2–4 hours, then replace the filter. Cost: $5–$25 for a new filter. If you haven't changed your filter in 90+ days, this is almost certainly your problem.