AC Not Cooling in Phoenix? Here's Why (and What to Do)
Updated for 2026 Phoenix summer season
Quick Answer
When a Phoenix AC runs but doesn't cool, the most likely culprits are a failed capacitor (outdoor unit hums but fan won't spin), low refrigerant, or a frozen/dirty evaporator coil. Start with the three checks below — if none resolve it, call a tech.
Step-by-Step: What to Check First
- 1
Thermostat settings
Make sure it's set to COOL (not HEAT or FAN ONLY) and the target temperature is at least 5°F below the current room temperature. If the display is blank, the batteries may be dead.
- 2
Air filter
Find the filter (usually at the return air vent or in the air handler). Pull it out. If it's grey and matted — replace it. A clogged filter can cause the evaporator coil to freeze, blocking all cooling. After replacing, switch the system to FAN ONLY for 2–3 hours to thaw any ice before switching back to COOL.
- 3
Outdoor unit
Walk outside and look at the condenser (the big box with a fan on top). Is the fan spinning? Is the unit making any noise? If the unit is completely silent, check your circuit breaker. If the unit hums loudly but the fan isn't spinning, you almost certainly have a failed run capacitor — a common, same-day-fixable repair.
- 4
Vents and airflow
Are all supply vents open? Check that furniture isn't blocking return vents. Restricted airflow forces the system to work much harder and can lead to freezing.
Common Causes & Typical Repair Costs
Failed run capacitor
$150–$350Outdoor unit hums but fan doesn't spin. Sometimes a clicking sound.
Typical turnaround: Same-day
Low refrigerant (leak)
$200–$600Ice on the refrigerant lines or evaporator coil. Warm air despite everything running.
Typical turnaround: Same-day
Dirty/frozen evaporator coil
$150–$300 (cleaning)Little to no airflow from vents. Ice visible on the indoor unit or copper lines.
Typical turnaround: Same-day after thaw
Faulty contactor
$150–$300Outdoor unit doesn't turn on at all even though the thermostat calls for cooling.
Typical turnaround: Same-day
Compressor failure
$1,200–$2,800Outdoor fan runs, but no compressor sound. System trips breaker repeatedly.
Typical turnaround: 1–3 days
When to Call a Tech (Don't Wait)
Phoenix indoor temps can exceed 100°F within a few hours of AC failure in summer. If any of the following apply, don't wait:
- ✓Anyone in the home is elderly, very young, or has a health condition
- ✓It's above 105°F outside and your home is already above 85°F inside
- ✓You've done the basic checks above and nothing resolved it
- ✓The outdoor unit won't start at all
- ✓You hear grinding, banging, or the breaker keeps tripping
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