Why Won’t My Lennox Air Conditioner Turn On?

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The Lennox air conditioner is a reliable cooling system, but there are times you may run into troubles such as it not turning on. What could be causing this problem? Below, we have listed the possible culprits causing this issue.

If your Lennox air conditioner doesn't turn on, it could be due to the following:

  • Failed Wall Thermostat
  • Bad Capacitor
  • Tripped Breaker
  • Blown Fuse
  • Failed Control Board
  • Bad Electric Contactor
  • Failed Run Capacitor
  • Bad Fan Motor
  • Broken Fan Blad
  • Clogged Air Filter
  • Dirty Evaporator Coils
  • Failed Thermostat Sensor
  • Dirty Condensor Lines
  • Refrigerant Leak
  • Bad Internal Thermostat

As you can see, there are several reasons as to why your Lennox AC unit isn't working. But, don't worry; in this article, we will explain the functions of each part and how it can affect your AC from turning on. In addition, we will answer other frequently asked questions about the Lennox air conditioner, so read on!

Air conditioners condenser units working on wall. Why Won't My Lennox Air Conditioner Turn On

Why Won't My Lennox Air Conditioner Turn On?

It can be frustrating when your air conditioning unit won't turn on, especially when you need it the most. There are many reasons for this, and we will explain the most common ones below:

blue collar air conditioner repairman working at residential home

Failed Wall Thermostat

The wall thermostat is the main component that controls when your unit turns on and off. It works by instructing the Lennox air conditioner to cycle on when it gets too hot in your home. If it fails, it won't transmit the message to the AC unit and will need to be replaced.

Bad Capacitor

The capacitor is an electrical component that helps maintain the current and voltage of the unit. If it malfunctions, your AC won't run properly and will need replacing. Likewise, if you notice your blower fan is noisy or overheating, this is a tell-tale sign.

Tripped Breaker

Sometimes the breaker on your home will trip without warning. To fix this, reset it by flipping it back to the "ON" position.

Blown Fuse

The fuse for your air conditioner is designed to protect the unit from receiving too much power. However, if it blows, then that means you have more electricity going into your system than what it can handle and will need to be replaced as soon as possible.

Failed Control Board

The control board is a pre-programmed chip that runs the AC unit. If it malfunctions, then your AC won't turn on at all. It will need to be replaced entirely for the Lennox air conditioner to function correctly.

Bad Electric Contactor

The electric contractor is a part that controls which wire gets power and when. If it fails, then the entire unit will shut off. Therefore, you will need to have it replaced for your air conditioner to function correctly again.

Failed Run Capacitor

The run capacitor helps the compressor get power when needed. If it fails, then you will need to replace it immediately. In addition, the bad capacitor can cause other parts in the unit to work improperly and will need to be replaced.

Bad Fan Motor

The fan motor is designed to produce the cool air you receive when using your Lennox air conditioning units. It will not cycle on and needs to be replaced right away.

Broken Fan Blade

The fan blade is just what its name implies--a blade that helps produce the cool air in your home. If it is broken or cracked, you will need to replace it as soon as possible. A broken fan blade can cause other problems within the system, so have it replaced right away.

Clogged Air Filter

The Lennox air conditioner uses an air filter to clean the air in your home. If it becomes clogged, the unit will not cycle on. If possible, you will need to replace it or have someone clean out the filter for you.

Dirty Evaporator Coils

The evaporator coil is what absorbs heat from the inside of your home and transfers it to the outdoors. If it becomes dirty, your Lennox air conditioner won't turn on. You will need to have someone clean out the coils for you if you can't do it yourself.

Failed Thermostat Sensor

The Lennox thermostat sensor helps detect when the air inside of your home has become too hot. If it is no longer functional, then your Lennox air conditioner won't be able to turn on because of this. You will need to have someone replace it for you if possible or buy a new one yourself.

Dirty Condensor Lines

The condenser lines are what expels heat from the unit outside. If they become dirty, your Lennox air conditioner will not cycle on because of this. You will need to have someone clean out the line for you if possible or replace them yourself.

Refrigerant Leak

The refrigerant helps the Lennox air conditioner produce cold air for your home. If there is a leak, you will need to replace it immediately. Also, your AC unit won't be able to turn on because of this and will need to be replaced if not taken care of right away.

Bad Internal Thermostat

The internal thermostat helps control the temperature of your AC unit. If it fails, your air conditioner will not turn on, and you will need to have someone replace it.

Outdoor Home Air-Conditioner. Why Won't My Lennox Air Conditioner Turn On

How do you reset a Lennox air conditioner?

There are two ways to reset the Lennox air conditioner. Let's take a look at the first one:

  1. First, turn off the wall thermostat.
  2. Next, turn off the power breaker that controls the AC unit.
  3. Now, wait a minimum of 30 seconds before turning the breaker back on.
  4. Once the breaker is turned back on, you can turn on the wall thermostat.

The second option is to reset the unit by pressing the pressure switch. The Lennox air conditioner doesn't have an actual reset button, but the pressure switch can help reset the unit. To do this, follow these steps:

  1. First, turn off the wall thermostat.
  2. Now, turn off the breaker to the AC unit.
  3. Next, remove the back panel of the AC unit.
  4. Once removed, look for a red push button at the unit's button on the copper line.
  5. Press that switch to reset the system.
  6. Once completed, you can turn on the circuit breaker and the wall thermostat.

If, for some reason, this doesn't work, then you may have another problem that may need to be addressed by a Lennox specialist.

How do you know if your AC fuse is blown?

A Lennox AC fuse, as you probably assume, is the part that helps control the power of your AC unit. If it blows, it can cause severe damage to your device and need to be replaced right away. The warning signs are typical if your unit won't turn on or make a humming noise.

To check if the fuse has blown, follow these steps:

  1. First, turn off all circuit breakers connected to the air conditioner.
  2. Next, turn off the unit itself.
  3. Locate the disconnect box [grey on the outside of the unit].
  4. Remove the disconnect box to expose the wires.
  5. Use a voltmeter to test the incoming and outcoming lines.
  6. If there is no power running through either line, the fuse might have blown, which means you will need to replace it.
  7. If you are unsure how to do all of this yourself, then turning off this device may be a good idea so that you can call up an expert Lennox technician for help.

air conditioner Technician/Electrician services outdoor AC unit and the Gas Generator. He checks the oil in the generator.

Why is my Lennox air conditioner running but not cooling the house?

One of the more common reasons your Lennox air conditioner is running but not cooling the house is low refrigerant, dirty evaporator coils, condenser blockages, or clogged air filter.

Let's take a look at all of these problems in more detail:

Low Refrigerant

If there is a leak in the Lennox AC unit, then this can cause the refrigerant to drop. Once it drops below a certain level, your Lennox air conditioner won't produce cold air and will need to be replaced if not immediately addressed.

Dirty Evaporator Coils

If your Lennox air conditioner is old, it can be due to dirty evaporator coils. This is why proper maintenance on your device needs to be done so that you don't experience problems like this.

Condenser Blockages

A condenser, which is typically located outside the house, can easily get clogged with dirt and debris. If this problem arises, you will need to have the device cleaned because it isn't efficient if there are clogged coils or lines.

Clogged Air Filter

A clogged air filter is another common reason your AC unit isn't getting cold. You or a specialist will need to remove the filter and clear it of all debris to fix this. This should be done once every month or two.

person wearing blue gloves is holding a heavily clogged dirty air filter in hands before replacing it with the new one

Final Thoughts

There are several troubleshooting tips that you should remember when dealing with your Lennox air conditioner. If it is making strange noises, has stopped working altogether, or if the house becomes hot during the night, then you need to act on one of these problems as soon as possible.

Remember, A Lennox AC unit can be delicate, and any mishandling can cause lasting damage that may require a complete replacement. To avoid this problem altogether, you need to take care of this device and perform regular maintenance, so it doesn't break down.

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