Direct Answer
If your AC is running but not cooling, the most common causes are: dirty filter, low refrigerant, failed capacitor, frozen coil, or broken compressor. Start with the simplest checks (filter, thermostat, debris clearing) before calling a technician. If you get no results, call same-day — running a failing AC can worsen the problem.
6 Reasons Your AC Is Running But Not Cooling
Here's how to diagnose the problem and when to call a technician:
Dirty or Clogged Air Filter
AC blows weak airflow, but house is warm
Look at the filter — if it's dark gray or black, it's clogged
Filters trap dust over 30–90 days. In Phoenix's dusty climate, filters clog faster
Replace filter ($15–$30) — do this yourself or call for service
Low Refrigerant (Leak)
AC runs but blows cool air instead of cold air
None — this requires refrigerant gauges and EPA certification
Small leaks in line sets, evaporator, or condenser coils. Arizona's heat accelerates leaks
Licensed tech locates leak, seals it, recharges system ($250–$500+)
Failed Capacitor
System won't start, or compressor shuts off after 10–20 seconds
None — high voltage risk. A tech can test in minutes
Capacitors degrade in Phoenix's summer heat. Most fail after 10–15 years
Capacitor replacement ($150–$300) — fastest, easiest fix
Frozen Evaporator Coil
AC blows warm air, and ice builds up on indoor unit
Turn system OFF. Leave it off for 4 hours to let ice melt
Low refrigerant, dirty filter, or blower motor failure causes ice to form
After thaw, replace filter, check refrigerant, test blower ($200–$500)
Failed Compressor
AC runs, fan spins, but no cooling at all and clicking sounds
Listen for clicking from outdoor unit — that's often a failed compressor
Compressors wear out over 12–15 years. Lack of maintenance accelerates failure
Compressor replacement ($800–$2,500) or full system replacement ($5,000–$10,000)
Thermostat Misconfiguration
Blower runs but compressor never starts
Check thermostat: is it set to COOL? Is setpoint above room temperature?
Wrong setting, dead batteries, or loose wiring
Check batteries, verify COOL mode, ensure setpoint is lower than current temp
Your AC isn't cooling and you're not sure why?
Call Sapper HVAC now — we can often diagnose over the phone and get you back to cooling same-day. (602) 206-7359
Call NowEmergency AC Tips While You Wait for a Technician
Don't keep running it
If the AC is not cooling and compressor won't shut off, turn the system OFF. Running it can cause major damage.
Close interior doors
Close doors to rooms you're not using. Concentrate cooled air in the spaces where you need it most.
Use fans
Ceiling fans and portable fans circulate existing cool air and create air movement.
Open windows at night
After sunset, open windows to let cooler air in. Close them first thing in the morning before it heats up.
Close blinds and curtains
Block direct sunlight, especially on west- and south-facing windows.