AC Not Turning On
Air conditioner completely unresponsive with no fan, no sounds, or display showing but nothing happens.
Quick Overview
DIY: 15 minutes | Professional: 1-3 hours
Summer
Common Symptoms
You might be experiencing this problem if you notice any of these signs:
- No sounds from indoor or outdoor unit
- Thermostat display is blank or dim
- No air coming from vents when AC is on
- Outdoor unit completely silent
- Circuit breaker is tripped
- Thermostat shows cooling but nothing happens
- Outdoor disconnect switch is off
- Previous power surge or storm
Step-by-Step Diagnosis
Follow these steps to identify the exact cause of your problem:
- Check thermostat display - if blank, replace batteries
- Verify thermostat is set to "Cool" and below room temperature
- Check main electrical panel for tripped breakers
- Look for outdoor disconnect switch near condenser - ensure it's on
- Inspect emergency shutoff switch near indoor unit
- Listen for any clicking or humming sounds from units
- Check for error codes on thermostat display
- Verify indoor unit has power (look for indicator lights)
- Test outdoor unit by listening for compressor hum
- Check if outdoor fan tries to spin but stops
- Inspect for visible damage to electrical components
- Note if problem started after weather event
Most Common Causes (Ranked by Likelihood)
Tripped circuit breaker
HIGH LIKELIHOODDead thermostat batteries
HIGH LIKELIHOODOutdoor disconnect switch off
HIGH LIKELIHOODFailed capacitor
MEDIUM LIKELIHOODBlown fuse in disconnect box
MEDIUM LIKELIHOODFailed contactor
MEDIUM LIKELIHOODThermostat wiring issue
LOW LIKELIHOODFailed transformer
LOW LIKELIHOODDIY Solutions
What You'll Need:
- None for basic checks
- Screwdriver (for disconnect box)
- Replacement batteries
- Flashlight
Time Required: 10-20 minutes
Step-by-Step Instructions:
- Replace thermostat batteries if display is blank
- Reset tripped breaker by turning fully off, then back on
- Check and flip outdoor disconnect switch to ON position
- Wait 5 minutes after power restoration before testing
- Set thermostat to Cool mode, 5 degrees below room temp
- If breaker trips again immediately, call professional
- Check indoor emergency shutoff switch near air handler
- Inspect fuses in outdoor disconnect box for burns
⚠️ Safety Warnings
- Never reset a breaker more than once - repeated trips indicate serious electrical problems
- Do not touch electrical components inside outdoor unit
- Turn off power at breaker before inspecting fuses
- If you smell burning or see scorch marks, call professional immediately
When to Call a Professional
Don't attempt DIY repairs if you experience any of these situations:
- Breaker trips repeatedly after resetting
- Burning smell or visible scorch marks
- Outdoor unit hums but won't start
- Clicking sound from outdoor unit with no startup
- Recent lightning strike or power surge
- No power to unit even with good breakers
- Thermostat wiring looks damaged
- Water leaking from indoor unit
Prevention Tips
Stop this problem before it starts with these preventive measures:
- Install whole-home surge protector ($200-500)
- Replace thermostat batteries annually
- Keep outdoor disconnect switch accessible
- Schedule annual spring maintenance
- Don't turn AC on immediately after power outage
- Label all HVAC breakers and switches clearly
- Keep emergency contact info for HVAC tech handy
Frequently Asked Questions
Why won't my AC turn on after changing the filter?
If your AC won't turn on after a filter change, you may have accidentally hit the emergency shutoff switch near the air handler, or the unit's safety float switch triggered from condensate backup. Check that all switches are in the ON position and look for standing water in the drain pan.
My AC won't turn on but the fan works - what does this mean?
If the indoor fan runs but the outdoor unit won't start, the problem is typically with the outdoor unit's electrical components (capacitor, contactor, or compressor) or thermostat wiring. This requires professional diagnosis.
How long should I wait after a power outage to turn on AC?
Wait at least 5 minutes after power is restored before turning your AC on. This allows the compressor oil to settle and pressure to equalize, preventing damage to the compressor.
Related Problems
AC Short Cycling
AC turns on and off repeatedly in short bursts instead of running proper cooling cycles.
AC Making Noise
Unusual sounds from AC unit including banging, grinding, squealing, hissing, or clicking noises.
Thermostat Problems
Thermostat display issues, unresponsive controls, incorrect temperatures, or HVAC not responding to settings.