It turns on and off automatically thanks to capacitors (which control motors) and a contactor (to turn the condenser on and off). Most residential HVAC systems use an air-cooled condenser, which passes air over the condenser coil to release heat.
Make sure the outside unit is turned on (there's probably a switch near the unit). If the outside unit has a separate circuit breaker, check your circuit box and make sure it hasn't been tripped. A more serious issue if the outside air conditioning unit's not working is a broken compressor, capacitor or fan.
Your thermostat not only sets your indoor temperature, but it also tells the AC units when to turn on and blow cold air. Make sure that the thermostat is on and that the screen is lit. If it's turned off, that's a simple fix.
In AC systems, the air conditioner reset button is on the outside unit's lower edge, typically close to the ground. Some models have the reset button located behind the service panel, which may require tools to remove. Reset buttons are usually red or yellow with a clear “reset” label.
FIND THE RESET BUTTON
In most cases, the small red reset button is inside the AC's compressor. If unsure, you can always refer to the user's manual to find the exact location.
If your outside AC unit is not turning on, it could be a thermostat issue. If your thermostat clicks but the AC does not turn on, you could have an issue with the thermostat itself. Broken thermostats often fail to properly communicate with the rest of your heating and cooling system.
Typically, you can find the switch for the indoor unit near your system's furnace or air handler. You can find the switch for the outdoor unit next to the outdoor unit, usually in a metal box on the exterior of your home.
Check Your Circuit Breaker
Locate your main circuit breaker and switch it back to the "On" position. Wait 30 seconds and turn on your air conditioner again. If it still doesn't work, you'll need to call a professional for help.
Blowing the fuse cuts the power to the unit to prevent electrical damage. If your AC has shut down and won't start again, especially if you've noticed odd electrical behavior immediately before the shutdown, chances are the fuse has done its job and will need to be replaced.
When the outside unit breaks down but the inside unit is running, the culprit may well be a broken compressor in the outside unit. That's typically a major repair, something that might even warrant a system replacement.
A sure sign of a bad AC capacitor is a humming sound from within the access panel. Any humming noises indicate a problem with the air conditioning system or the components of the AC unit. Try turning the power on and off again to see if it was a one-time issue with the motor or a recurring problem.
The AC fuse on most HVAC systems is typically on the unit's control board. You'll normally find the board behind an access panel on the unit's lower compartment. While you sometimes have to unscrew areas to access the control board, others have clips.
The main reasons your AC unit outside is not turning on could be something that has tripped the circuit breaker, something is blocking the fan's airflow, or the condensing unit is damaged. Other potential issues could be the thermostat isn't set correctly or the compressor could be malfunctioning.
The outside unit may not run if it's shut off or the safety switch is engaged. Worn parts, like fan motors or contactors, can prevent the unit from turning on. Debris inside or outside of an AC unit can keep it from running properly. If a bad compressor is to blame, you'll need to install a new cooling system.
In this case, there are two ways that you could notice a breaker switch for your HVAC system. The breaker switches will either be located in a breaker box in your garage or outside near the unit in a smaller metal box. Most of the time, there are multiple breaker switches.
A tripped circuit breaker can be a major cause of why an outside AC unit isn't turning on. This occurs when the current is too high in the outdoor unit, causing the breaker in the fuse box or main electrical panel to switch off power to the unit, resulting in it not receiving any electricity.
Look for it first around on the exterior of your machine, especially along the bottom edge near the ground. An AC's reset button is typically red and visible, so it should be easy to spot. If you don't see a reset button on the outside, it could be located inside the unit behind the service panel.
Common Reasons Why Your Air Conditioner is Not Turning On
Resetting your thermostat is often all that's necessary to get it working again. A tripped circuit breaker is another common reason why your AC won't turn on. Using too many appliances at once can trip the circuit breaker.
Look for a Tripped Breaker
If your AC won't turn on, you can check two places for a circuit breaker or electrical panel. Older homes have a main electrical panel on the outside of the home or a circuit panel on newer homes. Check the electrical panel to see if the breaker is tripped. Reset it if it is.
If your outside AC unit is not turning on, one of the most common (and simplest) reasons is an electrical issue like a tripped circuit breaker cutting the power to the unit. Other potential reasons with simple fixes include the thermostat being set incorrectly and the unit being low on refrigerant.
The short answer: Definitely not. (Unless you have manually engaged your outside fan to run constantly, but it shouldn't be running for hours on it's own.) If your HVAC is functioning correctly, it should keep your house cool by cycling on for 15-20 minutes at a time—with distinct pauses in between each cycle.
You'll want to have the unit examined for signs of a blown fuse, tripped circuit breaker, broken thermostat, or dirty air filters. Dirty or clogged filters commonly make AC compressors stop working. When it comes to operating your cooling system properly, be realistic with the temperature setting on your thermostat.
Let's start with the obvious – if your outdoor fan isn't getting ANY power at all, well…it's not going to spin! A tripped circuit breaker or blown fuse cutting electricity could easily be why that fan motor hasn't engaged. Loose or corroded wiring connections to the unit are another power problem to investigate.