Reasons Why My Air Conditioner Keeps Running

In this article, I will help you determine the various reasons your air conditioner is continuing to run. 2

Before we get into the exact parts and reasons why the air conditioner keeps running we need to determine what exact part of the air conditioner we are talking about.

When the person asks the question why does my air conditioner keep running? Are they referring to the inside blower motor or are they referring to the outside condenser? It could possibly be that the whole system inside and outside continuously runs. I will cover the whole system but it’s important to determine if it’s the inside and outside that stay on or just one part of the system.

Air Conditioner Keeps Running

Here are some basic tools you will need to troubleshoot and determine why your ac keeps running.

  1. Flat & Phillips screwdriver
  2. 1/4″ & 5/16″ nut driver
  3. Multimeter. A cheap $12 dollar one from Walmart works fine.

Here are the top reasons your outdoor condenser portion of your air conditioner keeps running.

Defective thermostat.

Your thermostat may be defective and send voltage to the outside condenser to stay on. If this is the case it’s easy to determine if this is what’s causing your air conditioner to keep running. What the qualified person needs to do is separate the face plate of the thermostat. On the vast majority of thermostats separating the control portion from the wall-mounted plate will stop the flow of low voltage. By stopping the flow of low voltage the signal going through the wires to the outside condenser may shut it down.

The low voltage thermostat wire goes from your thermostat to the control board on the inside unit. The inside unit may be an air handler or a furnace it doesn’t really matter. What does matter is preventing the thermostat from completing a circuit and sending a signal to the condenser to come on? In most applications, the yellow wire will be the wire sending voltage to the condenser. If the thermostat is defective the circuitry in the thermostat will not stop the flow of voltage.

Think of the thermostat as a light switch in your home. If the light switch is in the on position the light stays on. If the light switch is in the off position then the light will be off. However, if the internal metal contacts are defective then even when the light switch is off the light may still be on.

This is like the thermostat in which something on the inside of the thermostat is making a constant connection and not allowing it to turn off.

By removing the yellow wire or the whole face plate of the thermostat you will stop the flow of voltage to the condenser. Doing this will tell you if the thermostat is one of the problems. This may not be the only problem causing the air conditioner to keep running but it’s a good start to troubleshooting.

Stuck Contactor.

The contactor on the outside condenser may be the reason your air conditioner keeps running. The picture below is of a contactor that was stuck and causing the compressor and condenser fan motor to continue running.

Reasons Why My Air Conditioner Keeps Running?

In this situation, the contactor receives low voltage and when the thermostat reaches its desired temperature it stops the voltage. When the condenser air conditioner keeps running even after it hits its desired temperature it may be because the contactor is stuck.

As you can see in the picture the metal contacts can become burned and sometimes weld together. When the contacts stick together the condenser won’t shut off even when the thermostat stops the low voltage.

This picture directly below here is of a new contactor. The metal on the portion of this contactor is not burned or welded like the one in the above picture. If your air conditioner keeps running and you determine it’s the contactor that’s doing it then I would replace it with a new one.

Outside Air Conditioner Condenser Unit Not Turning Off
The air conditioner keeps running

Damaged low voltage wire.

If the wire going to your outside condenser has only 2 wires then this section doesn’t apply to you. The wires going outside would need a constant power (red) wire in the bundle. So if your low voltage wire only has 2 wires skip this section.

The low voltage wire is the wire that feeds low voltage to your outdoor condenser. In many parts of the country, the low-voltage wires come out of the house and swing over to the condenser. Some contractors don’t cover the low voltage wires and they can become sun rotted and damaged. If the sun dry rots the wires and the copper is exposed it may fuse together causing the voltage to keep the condenser on.

why does my ac keep blowing the 3 amp fuse
Low voltage HVAC communicating wire

The sun, rain, and elements can deteriorate the insulation and expose the copper. If that happens there is a potential for the copper wires to touch. Most of the time when this happens the copper touches and the fuse on the inside circuit board blows.

In the case of the air conditioner keeps running it would be only 2 wires touching that send voltage to the contactor. This type of situation doesn’t happen very often but when it does happen it’s often the last thing to be checked.

Simply inspect the wire outside going to the condenser to ensure the wire has no broken insulation or defective splices. If the wire appears in good condition this is most likely not the problem.

Defective circuit board.

The circuit board may be defective and cause the air conditioner to keep running. The picture below is of a fried circuit board that caused some strange problems in the system I took out. When a circuit board goes bad you may experience several different problems. One of those problems may be the cause of why your air conditioner keeps running.

why does my air conditioner keep running
why does my air conditioner keep running

Here is a picture of a circuit board that has nothing wrong with it. Sometimes the board appears to be in good shape however the relay may be stuck internally. If that’s the case you will need a voltage meter to troubleshoot the board.

my does my air conditioner keep running
good air conditioner circuit board

The air conditioner keeps running conclusions.

When trying to troubleshoot and determine the reason your air conditioner keeps running It’s important to take your time. Take your time and start at the thermostat and go through the sequence of operation of the air conditioner.

Remember to think of the thermostat as a light switch. The thermostat sends voltage through specific wires to engage various components. When the green wire has voltage applied it will turn on the inside blower motor. When the yellow wire has voltage applied the condenser will come on.

With this in mind, you can go to the various components and determine what needs to be repaired or replaced.

I hope this post helped you in some way.

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