Why Air Conditioning Unit Won’t Turn On? 3 Troubleshooting Steps

Everyone would want their AC to serve them faithfully, but one day your trustworthy unit might fail to even turn on.

There are quite a few reasons that can make your cooling unit refuse to kick in, including issues with the thermostat, a dirty filter, low refrigerant levels, a faulty capacitor or motor, and a clogged drain pan. However, the first thing that you should do is make sure that the AC is actually receiving power.

Below you will find out how to turn your air conditioner on manually and whether a simple reset is going to help.

Why Air Conditioning Unit Won’t Turn On?

Issues with the thermostat

In a lot of cases, your AC won’t turn on simply because the thermostat is not set to ‘cool’ or because the set temperature is not low enough. You might also want to make sure that there are no loose wires in the device and that it’s clean.

Read: Does Closing AC Vents Save Electricity?

Low refrigerant levels

If the level of refrigerant in the cooling system drops below a certain point, the unit’s compressor might refuse to start. Do bear in mind that the substance does not get used up during the AC’s operation which means that your system most likely has a leak.

A dirty air filter and/or frozen evaporator coil

A clogged filter will restrict airflow and this, in its turn, can make the system overheat. Another thing that can happen if the airflow is blocked is the evaporator coil will freeze up. If that’s the case, then the unit might not start, until the ice thaws.

Read: Are HVAC Service Plans Worth It? 

A faulty capacitor

A capacitor is an element that provides the initial jolt of electricity your air conditioner needs to run successfully. Capacitors can get damaged due to general wear and tear, after a power surge, or if the unit overheats. 

The AC is switched off

Your air conditioner has an on/off switch just like any other appliance. Make sure that the unit is turned on and check the circuit breaker.

A dirty outdoor unit

The part of the system that is located outside can get clogged with debris over time. If the condenser is dirty, it might trip the circuit breaker whenever you try to turn the AC on.

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A clogged drain pan

The float switch will get triggered if the drain pan is clogged and this will prevent your unit from turning on.

A damaged motor

You won’t have any airflow if the blower motor is faulty. A damaged motor can also make the circuit breaker trip.


If your air conditioner is around 15 years old, then it might be time to get a new unit. The old system might have simply broken down.

Read: How To Do Air Balancing HVAC In A House?

The Outside AC Unit Won’t Turn On

The outdoor unit has a different power source than the indoor unit. That’s why the first thing that you need to do is make sure that the outside shut-off switch is not in the ‘off’ position.

Some outside units have a reset button, so you might want to try pushing that as well.

Check the unit for any blown fuses and ensure that it’s turned on at the circuit breaker. Finally, clear the area around the outdoor unit; you might also have to clean the component.

The Inside AC Unit Won’t Turn On

  1. Check for a tripped breaker or a blown fuse. 
  2. Replace the air filter, if necessary.
  3. Check the thermostat settings. Your AC will not kick in until the room temperature rises to a certain level. To test if that’s the issue or not, lower the thermostat’s temperature even more.
  4. Inspect the condensate line and clean it, if there is such a need.

Read: Is Closing Vents Bad For HVAC?

The Window AC Unit Won’t Turn On

Find the cord coming out of your window AC. The unit might simply not be plugged in or the actual cord can be damaged.

The AC’s coils and fins can trap a lot of dust and dirt over time, and insufficient airflow, in its turn, will prevent the unit from turning on. Clean the air conditioner and replace the air filter.

AC Won’t Turn On But Fan Does

If your air conditioner is only capable of being in fan mode, then one of the following issues might be to blame:

  • A damaged compressor
  • A dirty coil and filter
  • A broken capacitor
  • Insufficient power supply

You might also want to check the wire connections between the indoor and outdoor units. If they’re not able to ‘communicate’, then the AC might not turn on, even though the fan will be running. 

How to Manually Turn On AC Unit?

A lot of us are used to turning the air conditioner on by pushing a button on the remote control. However, you should not panic, if that doesn’t happen, as you can always try turning the unit on manually.

  1. Locate the power box and make sure that the breaker labeled ‘AC’ is flipped to ‘on’.
  2. Find the power cord that’s coming from the compressor. Ensure that the cord is plugged in.
  3. Locate the AC’s power button. It can typically be found on the front side of the unit (closer to the bottom). Press the button and hold it for a few seconds – you should hear the system kick in.
  4. On some units, you might also be able to manually lower the temperature. If there is a lever or a knob on the front side of the AC, use it to set the desired temperature. 

Read: How To Remove And Replace Attic Insulation That Fell Off?

How Do You Fix an Air Conditioner That Won’t Turn On?

There are a few things that any homeowner can check if the air-conditioning unit is not turning on:

  • Check the power supply (once you’ve inspected the circuit breaker, don’t forget about the regular AC switch)
  • Double-check the thermostat settings (the device should be set to ‘cool’, the fan – to ‘auto’, and the set temperature should be lower than the current room temperature)
  • Replace the filter, if you have noticed that it’s dirty
  • Clean the area around the outdoor condenser

All the other steps, like checking the refrigerant level, the compressor, and so on, should, ideally, be performed by an HVAC technician. 

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How Do I Reset My AC?

Sometimes, your air conditioner will kick in after a quick reset.

A lot of newer models come equipped with a designated reset button, so all you would have to do is press and hold the button to reset the system.

You can also choose to turn your AC off at the circuit breaker. First, turn off the unit at the thermostat and then flip the breaker responsible for the air conditioner to the ‘off’ position. Wait for at least a minute before flipping the breaker back and then give the cooling unit 30 minutes to get back to normal operation.

How Do I Know If My AC Fuse Is Blown?

If your AC has a blown fuse, then the outdoor unit won’t turn on.

If you have experience working with electricity, then you can test the fuse with a multimeter. Check the voltage on the ‘load’ side (place the leads on the load wire lugs). If the reading is zero, then the fuse is blown. 

What Blows the Fuse in an Air Conditioner?

  • Loose electrical connections
  • A clogged filter
  • A faulty capacitor
  • Low levels of refrigerant
  • A malfunctioning condenser fan

Is My AC Broken or My Thermostat?

Sometimes, if an air conditioner is not turning on, it’s not the actual cooling equipment’s fault. A broken thermostat can also prevent your AC from kicking in.

The most common signs of a malfunctioning thermostat include:

  • The thermostat has a non-responsive or a turned-off display
  • The heating or cooling system is not responding to changes in thermostat settings
  • The thermostat doesn’t match the room temperature
  • The device forgets the programmed settings


A malfunctioning thermostat, a dirty filter, and issues with the power are the most common reasons for an AC not turning on.

If the problem didn’t get fixed after you checked the things mentioned above, then it looks like you would have to call an HVAC technician.