An AC unit humming but not turning on is often caused by a faulty capacitor, a tripped circuit breaker, or a malfunctioning compressor. When the AC capacitor fails, the fan motor does not receive power, resulting in a noticeable humming or buzzing sound.
If the capacitor is faulty or damaged, the motor may struggle to start, resulting in a humming noise. Loose or Damaged Wiring: Loose or damaged wiring can disrupt the flow of electricity to the motor, causing it to hum without starting properly.
This problem of getting a humming noise along with little to no spinning is very common with motors that do not have good quality capacitors. You should replace the capacitor with a good one and the blower motor will work smoothly. Once again, this may initially trace back to a simple blocked filter.
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.
If your air handler is running but not blowing air, there are two likely scenarios: either a broken AC blower belt or an issue with the motor itself. If the air handler is humming or buzzing but not making the mechanical sounds of a motor running, you're most likely talking about an issue with the motor itself.
An AC unit humming but not turning on is often caused by a faulty capacitor, a tripped circuit breaker, or a malfunctioning compressor. When the AC capacitor fails, the fan motor does not receive power, resulting in a noticeable humming or buzzing sound.
It's a small, red button usually located on or around the unit. The button should have a clear 'reset' label. Once you find the button, press it for around three seconds and observe the AC. Check whether the AC kicks on immediately and if it doesn't, press the button again for another three seconds.
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 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.
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.
If the voltage supplied to the motor is lower or higher than what's required, the motor might hum but not start. Under-voltage doesn't provide enough amperage to the air compressor motor, and over-voltage could cause overheating or damage to the motor windings.
If this describes your situation, you most likely have a bad fan capacitor. A damaged capacitor will prevent the AC fan motor from receiving power. Then, the system can't transfer and dump heat from inside your home outdoors, which is why you feel warm air blowing out of your vents.
Refrigerant pipes are vibrating – If the refrigerant lines are undercharged, it can cause vibration. This vibration may sometimes sound like a humming noise. There may be other causes for a vibrating refrigerant line, like an improperly mounted expansion valve.
If the motor hums but doesn't run, and if it's hard to turn, its because the bearings are seized. If it hums and turns freely but doesn't run, then it's probably the capacitor connected to the motor, and if it doesn't even hum, it's the motor's thermal fuse, switch, or power cord.
If, on inspection, you hear chattering, whining, squealing, chirping, or rattling sounds coming from the AC compressor, it is time for AC service. Sometimes the commotion only erupts when you engage the AC switch. Some noises remain constant. Compressor noises result from either a faulty clutch or a seizing shaft.
A faulty capacitor – whether it's the wrong size, blown, or damaged – can be the root cause of your motor hum. Solution: Test and replace any faulty capacitors. Both the start and run capacitors are usually located on the exterior of the motor housing, often in dedicated metal or plastic casings.
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.
AC Fuse, Circuit Breaker, or Relay Replacement Cost
Expect to pay between $15 and $300 to have AC fuse and circuit breaker issues addressed or relays in your AC unit replaced. These projects do not usually take more than a couple of hours.
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.
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.
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.
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.
The easy explanation for your AC not turning on is a thermostat issue. Double check your thermostat is on, set to “cool,” and that the temperature is set to a few degrees colder than the normal ambient temperature of your home. You may also need to replace the batteries.