Why "Running But Not Cooling" Is So Common in Arizona
In extreme heat, your AC system is working at or beyond its design limits. A system sized for a 95°F design day struggles when temperatures hit 115°F. That's why "running but not cooling" calls spike in July and August — it's not always a broken system. Sometimes it's a system that's simply overwhelmed. Here are the seven most common causes.
1. Dirty or Clogged Air Filter
A clogged filter restricts airflow across the evaporator coil. When airflow drops, the coil can't absorb heat efficiently — and in extreme cases, the coil freezes over, completely blocking airflow. Check your filter first. In Arizona, 1-inch filters should be replaced every 30–45 days during peak season.
2. Low Refrigerant (Refrigerant Leak)
Refrigerant is the substance that absorbs heat from your home's air. When the charge is low — almost always due to a leak — the system loses cooling capacity. Signs include ice on the refrigerant lines, hissing sounds near the unit, and warm air from vents despite the system running. This requires a licensed technician to diagnose and repair.
3. Dirty Condenser Coils
The outdoor condenser unit releases the heat absorbed from your home into the outside air. When the condenser coils are coated with dust, cottonwood, or haboob debris, they can't release heat efficiently. The result: the system runs longer and can't keep up. Bradford cleans condenser coils as part of every tune-up.
4. Failed Capacitor
Capacitors are small cylindrical components that start and run the compressor and fan motors. They're one of the most common failure points in Arizona — extreme heat degrades them faster than in cooler climates. A failed run capacitor causes the compressor or fan to run inefficiently or not at all. Bradford technicians carry replacement capacitors on every service truck.
5. Undersized System
If your system was improperly sized when installed — or if you've added square footage, windows, or insulation changes since installation — it may simply not have enough capacity for your home. This shows up most clearly on 110°F+ days when the system runs continuously but can't get below 80°F inside.
6. Duct Leaks
Leaky ductwork in an unconditioned attic (which can reach 160°F in Arizona summers) allows cooled air to escape before it reaches your living space. A system can be perfectly functional and still fail to cool your home if 20–30% of the conditioned air is leaking into the attic.
7. Thermostat Issues
A miscalibrated or failing thermostat can misread the room temperature, causing the system to short-cycle (turn off before the space is cooled) or run at the wrong times. If your thermostat is more than 10 years old and you're having cooling issues, it's worth testing or replacing.
When to Call Bradford
Causes 1 and 7 you can often address yourself. Causes 2, 3, 4, 5, and 6 require a licensed technician. If your system is running but not cooling and a filter change doesn't help, call Bradford at (623) 624-6246. Same-day service is available for most calls received before 3PM.