Why Won't My AC Turn On?
An AC that will not start usually has a thermostat problem, a tripped breaker, or a safety switch that shut it down because water backed up. Check the thermostat first. Put in fresh batteries and set it to COOL. Then check the breaker panel and reset a tripped breaker once. If that does not do it, call.
What stops an AC from turning on?
Dead thermostat batteries or wrong settings
If the thermostat screen is blank or dim, the system never gets told to cool. A mode left on HEAT or OFF does the same thing. Fresh batteries and a look at the mode and the temperature setting are the first steps, and both are safe.
Safe to check yourselfTripped circuit breaker
The outdoor unit and the indoor unit are usually on their own breakers, and a storm or a power surge can trip either one. Reset a tripped breaker one time only. If it trips again, there is an electrical fault. That needs a technician, not another reset.
Safe to check yourselfTripped water safety switch
Your AC makes water as it runs, and that water drains away through a pipe. Most systems have a small switch in the drain pan that cuts the power if the water backs up. You can look near the indoor unit and see whether the pan is holding water. Clearing the drain is our job.
Safe to check yourselfBlown low-voltage fuse
A small fuse on the control board protects the low-power circuit that runs your thermostat. A thermostat wire nicked outside by a shovel or a trimmer will blow it. Putting in a new fuse without finding the damaged wire only blows the next one. We trace it.
Technician repairFailed capacitor
The capacitor is the part that gives the motors the push they need to start. When it weakens, the outdoor unit may hum or click but never spin up. A capacitor holds an electric charge even after the power is off, so testing it is technician work.
Technician repairFailed contactor
The contactor is the heavy switch that sends power to the outdoor unit when the thermostat calls for cooling. When its contacts burn or stick, the unit stays silent even though the rest of the system is fine. Checking it means working inside a live electrical box.
Technician repairDamaged wiring or a safety lockout
Chewed or damaged low-power wiring, or a control board that has locked itself out after repeated faults, will keep the system from starting. These hide inside cabinets and wall runs. Tracing them takes a meter and training.
Technician repairWhat can you check yourself?
- Put fresh batteries in the thermostat and see whether the screen comes back on.
- Set the mode to COOL and drop the setting at least five degrees below the room.
- Find the breakers marked for the AC and the indoor unit. If one is tripped, reset it one time only.
- Look at the drain pan under the indoor unit. Check whether it is holding water or the safety switch has tripped.
- Wait five minutes after any change. Most systems hold off for a few minutes to protect the compressor.
Safety note: If a breaker trips again after one reset, leave it off and call. A breaker that keeps tripping is protecting you from an electrical fault.
When should you call for repair?
Call when the thermostat has fresh batteries and the right settings, the breakers are on, and the system still will not start. Call right away if a breaker trips a second time, if the outdoor unit hums or clicks without starting, or if you smell anything burning near the equipment. Each of those points to an electrical fault, and none of them is safe to chase on your own.
The older side of Rockville is full of 1950s ramblers in Twinbrook and College Gardens, and the age of the electrical panel matters in them. A modern outdoor unit often got added to wiring laid out for a much smaller house. A summer storm flickers, the breaker trips or the capacitor dies, and the AC will not start. Check the panel and the outdoor shutoff box first. If the breaker trips again after one reset, stop and call.
Related questions
Why is my thermostat screen blank?
A blank screen usually means one of four things. Dead batteries. A tripped breaker on the indoor unit. A tripped water safety switch. A blown fuse on the control board. Change the batteries and check the breaker first. If the screen is still blank after those two steps, the low-power circuit has a fault we need to trace.
Why does my AC breaker keep tripping?
A breaker that trips again and again is protecting you from a real fault. It could be a shorted compressor, a failing motor, damaged wiring, or a seized fan. Reset it one time only. If it trips again, leave it off and book a visit. Holding or resetting it over and over can overheat the wiring.
The outdoor unit hums but will not start. What does that mean?
A unit that hums and never spins up usually has a failed capacitor or a stuck fan motor. The hum is the motor trying to start without the push it needs. Turn the system off at the thermostat so the motor stops straining, then book a repair. A capacitor holds a charge even with the power off.
How long should I wait after resetting the breaker?
Give it about five minutes. Most outdoor units hold off for a few minutes after power comes back, so the compressor does not restart under pressure. If nothing runs after ten minutes with the thermostat calling for cooling, the problem is somewhere else and it is time to call.
If your AC still will not turn on after these checks, call Mora Heating & Air and we will find the fault.
Or tell us what your system is doing
Send us the details and we will call you back. If the house is very hot or very cold right now, calling is faster.