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.
If your AC unit has a reset button on the condenser unit, you simply press it and hope that the problem resolves. 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.
Check the circuit box in your home to make sure the breaker for the outside unit hasn't tripped. If it has, turn it all the way off, then flip it back on. If this happens more than once, you'll want a licensed electrician to determine why the breaker keeps tripping. This could be a fire or safety hazard in the making.
If you think your air conditioner has blown a fuse, the first sign you'll notice is that the outside AC unit is inoperable. The best way to check for a blown fuse is by using a voltmeter. Be warned — you are working with live electricity and should use extreme caution when troubleshooting your system.
Check the thermostat
You should check if it's been set to the correct temperature and also make sure it's set to “cool”. If the AC settings are not right, it won't turn on. You can also check if the batteries in the thermostat are fresh and replace them if needed.
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.
Turn the system off through the thermostat or breaker to do a reset. Wait for a minute before turning it on again. Check if your cooling unit is back to normal. If it isn't, hire an HVAC technician to help you with further troubleshooting.
Look for a RESET Button.
Some systems have a RESET switch on the outside unit. You can push this and see if it helps. If your unit does not, you can turn off the system at the thermostat, wait 5 minutes, and try again.
A central AC system consists of indoor and outdoor units. An indoor air handler can continue running when the outside unit has shut down. While air will blow from the vents, it won't be cooled; it may be as warm as the summer air outside.
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.
Shut off your system by hitting the isolation switch, wait 30 to 60 minutes and then turn it back on. This manual reboot fully disconnects your AC unit from power, allowing all electrical components to reset.
An outside AC fan not spinning could be caused by power supply issues, a faulty capacitor, a burnt out motor, contactor issues, wiring problems, debris or obstruction, a faulty thermostat or control board, or frozen evaporator coils. Contact your local Carrier dealer to help troubleshoot the issue further.
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.
Check these issues when the unit won't kick on: Check the thermostat and adjust the settings if it isn't set to Cool and an appropriate temperature setting to call for cooling. Examine the house circuit breakers for the AC unit and reset any tripped breakers. Check the air filter and replace the filter if it's dirty.
If your thermostat is set to cool but your AC isn't turning on, there could be several potential causes ranging from a simple tripped breaker to more complex refrigerant or compressor issues. Start with the basics, like checking the thermostat settings and power supply, and work through more detailed troubleshooting.
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.
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.
There are a number of reasons why your AC unit may stop working unexpectedly, including electrical problems, blockages, thermostat issues, and more. Troubleshooting includes checking your circuit breakers, thermostat settings, and replacing your air filters.
This can happen if the system is set to "fan only," causing only the inside fan to circulate air without engaging the outside unit to cool the air. Other thermostat settings that can lead to similar problems include incorrect time or day settings, or an unresponsive touch screen.
There are a few reasons why this might happen. Some of the simpler causes may be that a vent is closed, or that the thermostat needs fixing. Some more major causes may be that the unit is low on refrigerant, signaling a leak, or that there is a problem with the fan.
One AC, Two Breakers
Most central air-conditioner systems incorporate two circuit breakers. One protects interior components such as the air handler/blower fan inside the house. Another circuit breaker protects the outdoor condenser unit, including the compressor.
It's important to be able to recognize the signs. If your device suddenly stops working, it could be a blown fuse. Check for discoloration or markings on the fuse. If you see any damage, there's a good chance the fuse needs to be replaced.
Depending on the severity of the issue, the cost to replace an air conditioner fuse, including installation, ranges from $100 to $300 or more.