Cooling Emergency
AC Won't Turn On at All?
You set the thermostat, nothing happens. No fan, no compressor, no air. Here's what to check before you panic.
What's Going On
Understanding the Problem
You're adjusting the thermostat and getting nothing — no fan, no air movement, no sound from the outdoor unit. The house is getting hot and the system seems completely dead. This can be caused by something as simple as a tripped breaker or as complex as a failed control board.
Diagnosis
Common Causes
1Tripped circuit breaker
Power surges, storms, and electrical issues can trip the breaker for your HVAC system. Most homes have separate breakers for the indoor air handler and outdoor condenser — both need to be on.
2Thermostat lost power
If your thermostat screen is blank, it may have dead batteries or a wiring issue. Without the thermostat sending a signal, the system won't start.
3Safety switch tripped
Your AC has several built-in safety switches. If the condensate drain pan is full (float switch), the system shuts off to prevent water damage. This is common in Houston's humidity.
4Blown capacitor
The capacitor gives the compressor and fan motors the boost they need to start. When it fails, the system tries to start but can't. You might hear a clicking or humming sound. This is very common in Houston summers due to the extreme heat load on the system.
5Contactor failure
The contactor is an electrical switch in the outdoor unit that turns the compressor on when the thermostat calls for cooling. Worn contacts or burnt coils prevent the signal from reaching the compressor.
6Blown fuse in disconnect box
There's a disconnect box on the wall near your outdoor unit. Inside are fuses that can blow during power surges. If these are blown, the outdoor unit gets no power even when the breaker is on.
DIY Troubleshooting
What You Can Try
Check the circuit breakers
Go to your electrical panel and look for breakers labeled AC, HVAC, Air Handler, or Condenser. If any are in the middle (tripped) position, flip them fully OFF, then back ON. Check both indoor and outdoor unit breakers.
Check the thermostat
If the screen is blank, replace the batteries. If it's hardwired and blank, check the breaker for the air handler (the thermostat is powered by the indoor unit's transformer). Try setting it to COOL and lowering the temperature 5 degrees below room temp.
Check the condensate drain pan
Look at the drain pan under your indoor unit (usually in the attic or utility closet). If it's full of water, the float switch has shut the system off. You can carefully empty the pan and try restarting, but the clogged drain line still needs to be cleared.
Check the outdoor disconnect
Find the gray metal box on the wall near your outdoor unit. Open it and check if the pullout switch is in place and the fuses look intact. If a fuse looks burnt or blackened, that's your problem — but replacing it requires a tech.
Wait 5 minutes after a reset
If you reset a breaker, give the system 5 full minutes before expecting it to start. AC systems have a built-in time delay to protect the compressor from short-cycling.
Know When to Call
When to Call a Pro
If the breaker keeps tripping when you reset it, stop resetting it — there's an electrical problem that could damage the system or cause a fire. If you hear clicking or humming but the system won't start, it's likely a capacitor or contactor and needs professional repair. In Houston heat, no AC is an emergency. Call us.
Pro Tip
After a Houston thunderstorm or power outage, many AC systems won't restart automatically. This doesn't mean something is broken — the safety delay just needs to time out. Wait 15 minutes after power returns before worrying. If it still won't start, check the breakers.
More Troubleshooting
Other Common HVAC Issues
AC Keeps Tripping the Breaker
Resetting the breaker only for it to trip again minutes later? Stop resetting — here's what's going on.
Read guide →HVAC After a Power Outage
After a Houston storm or power outage, your HVAC system may need a manual reset. Here's the step-by-step.
Read guide →Thermostat Screen Blank
No display, no response, no HVAC. Here's how to troubleshoot a dead thermostat.
Read guide →