Quick Checks
Thermostat on COOL and AUTO
Set the mode to Cool, the fan to Auto, and the temperature at least three degrees below room temperature. If the fan is set to On, it blows room-temperature air between cycles.
Check both breakers
Central AC has a breaker for the indoor unit and a separate one for the outdoor unit. If the indoor fan runs but the outdoor unit is silent, check the outdoor breaker and the disconnect box next to the unit.
Replace the filter
A blocked filter starves the coil of air. The coil can freeze and the air turns warm. Replace it, then let the system run with the fan only for a few hours if you see ice.
Look at the outdoor unit
With the system calling for cooling, the outdoor fan should spin and you should hear the compressor. A humming unit with a fan that doesn't spin often means a failed capacitor.
Common Causes
Failed capacitor
Call ProThe most common summer failure. The outdoor unit hums but the fan or compressor won't start. It is a quick part replacement for a technician.
Frozen evaporator coil
DIYLow airflow from a dirty filter or a slow blower lets the coil ice over. Turn cooling off, run the fan, fix the airflow cause. Repeated freezing can also mean low refrigerant.
Clogged condensate drain or tripped float switch
DIYMany systems have a safety switch that shuts cooling off when the drain backs up. Clearing the line restores cooling.
Bad contactor
Call ProThe contactor is the switch that powers the outdoor unit. When its contacts burn or stick, the unit won't start or won't stop.
Thermostat problem
DIYDead batteries, a loose wire or a wrong setting after a power outage can stop the call for cooling.
Low refrigerant from a leak
Call ProIf the coil keeps freezing or the air is only slightly cool, the system may be low on refrigerant. Adding refrigerant without finding the leak is a temporary fix.
When to Call a Professional
- The outdoor unit hums but the fan doesn't spin.
- The breaker trips again after you reset it once.
- Ice returns on the coil or refrigerant lines after thawing.
- You smell burning or see scorch marks: turn the system off first.
- New systems, replacements and ductwork: we will point you to a licensed specialist.
Safety Warning
Turn off power at the thermostat and the outdoor disconnect before any inspection. Never touch the capacitor; it can hold a charge after power is off. Don't reset a breaker more than once.
Estimated Repair Cost
The AC service call is free. The technician finds the cause and gives you the exact repair price before any work starts. Nothing is done without your approval.
Frequently Asked Questions
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