So for my next edition of the ‘Ask The HVAC Tech’ newsletter. I answer a question from Marion H. from Springfield, IL, who is experiencing air coming out of her air vents even though the AC is not running. There are a few reasons why this will happen, which I will go over in detail below.

So imagine you’re at home, and there is air coming out of the vents, even though your air conditioner is switched off. It’s an odd sensation, and many individuals have been baffled by this question. The solution, it turns out, is relatively straightforward.

There are 3 possible explanations as to why air is coming out of your vents while the AC is off: 1) is that the unit has electrical difficulties. 2) It’s also conceivable that you mistakenly set your air conditioner’s fan to ON rather than AUTO. 3) Your thermostat may cause the issue.

So, if you want to know if you can solve this problem on your own, and save time and money without calling an AC tech, it’s recommended that you continue to the end of this page to understand how to go through each of these troubleshooting steps first. 

Let’s get started without further ado!

Reasons Why Air Can Come Out of Vents While Your AC Is Off

It is inconvenient to have an air conditioner that constantly blasts air even when switched off. Furthermore, it continues to use energy.

There are three major reasons for this problem are:

1. Electrical Problems

Problems are mainly caused by the wiring or elements of an air conditioner. And these usually need the assistance of a certified specialist. However, before consulting a professional, you should inspect your air conditioning unit if you are comfortable with opening the system.

Look for any obvious electrical problems, like burned wires, disconnects, cut wires, signs of burning, etc… Any of these could trigger the continual blowing of air, even if the system is off.

• Contactor Problems

The contactor is a component of an air conditioning unit that regulates the flow of electricity into its components, mainly the compressor and condenser. It may become stuck if you do not regularly clean and maintain your air conditioner. 

You might want to consult with an HVAC specialist on this one. As touching wires are components that could give you a strong electrical shock if you don’t disconnect and terminate power to the unit altogether.

• The fan motor has failed.

If your air conditioner is switched off and producing airflow, power regulation to either or both of the inside and outside fan motors could malfunction. A faulty fan motor will result in overall airflow concerns, such as your current issue. So either a switch that controls the power to the fans is stuck, or there is a ‘disconnect’ of sorts to the power control to the fans.

• Wiring Problems

To add to the previous issue, damage to any of the air conditioner’s wiring might result in short circuits or disconnection from any place in the unit, so if you see what looks like damaged wires, corrosion, rust, etc.. on the wiring, then it will be good to call out an experienced AC tech. Wear and tear, amateur repair efforts, and power outages can all cause damage.

• The circuit breaker has been tripped

This is just a matter of power. It is usually due to an overheated circuit breaker, which causes the air conditioner to shut off. You can fix it in a minute by flicking the breaker switch if you see that it is tripped. It may, however, be far worse.

In this instance, you may want the assistance of a specialist, especially if it trips regularly.

• Start Capacitor And Run Capacitor

In an air conditioning machine, there are two types of capacitors: start and run, which need differing amounts of energy to keep the motor going. If your capacitor is malfunctioning, this might be the source of your air conditioning difficulties. 

• Issues With The Fuse

Perhaps some dust and dirt are already interfering with your fuse’s connection – it’s possible that you haven’t cleaned or vacuumed in a long time.

2. The Thermostat Is Out of Date

This is not as prevalent as electrical issues. A thermostat, like any other electrical device, can degrade and fail. It may often survive up to ten years, although it can begin to malfunction owing to subtle changes, average age, wiring difficulties, or dust buildup.

Over time, relay switches might get blocked or destroyed, rendering the thermostat’s communication with the fan impossible. It means the fan is not receiving the orders you provide to the thermostat.

As a result, even if your air conditioner is turned off, it could cause the fan to run continuously. It will, in particular, continue to blow air to your vents even if you repeatedly try to turn it off.

Furthermore, it is uncommon for thermostats to turn off when the air conditioner is turned on, but it is possible. 

Be aware that issues may still arise even if the thermostat is brand new.

3. Inadvertently turned on the fan

When cleaning, there are times when you may inadvertently switch something on.

For example, you may have set the fan on your air conditioner to On rather than Auto. After you turn it on, your fan will continue to blow air even when it is turned off. If you discover this is the problem’s actual cause, you must return it to Auto.

How To Stop Air Coming Out of Vents When the AC Is Off

Stopping the chilly airflow from the vents when the heat is turned off is typically a simple remedy. Simply switch your thermostat’s fan setting from ON to AUTO.

By adjusting the fan speed, you are effectively instructing the furnace’s blower motor to work only when it creates heat during its heating cycles (the furnace usually cycles between 3 and 8 times per hour).

When the fan is turned on, air will stream out of the vents only when the furnace actively burns natural gas to create heat.

On the other hand, the fan will not force air through the vent when the furnace is turned off since the furnace solely powers it.

Switching the fan to AUTO will help minimize your monthly energy expenditures because it will only work while the furnace is actively operating.

If changing the thermostat fan setting does not resolve the problem, you may have a more serious issue. In that circumstance, the best course of action is to contact an HVAC professional. They have the necessary knowledge, expertise, and abilities to isolate and resolve issues appropriately.

Once the problem has been identified, they can advise you on the best course of action and proceed with the repair. In addition to repairing the problem, an HVAC specialist can ensure that your system is in good working order.

Alternatively, see this instruction if your furnace spews chilly air while the heat is turned on.

If your furnace isn’t working correctly or requires HVAC repair, we recommend having an HVAC professional inspect your system.

How Do I Prevent My AC From Blowing Air When off in the Future?

The simplest and most important thing to keep your air conditioner in excellent working order is to replace the blocked air filter! Set quarterly reminders and keep backup filters on hand for quick swaps.

It’s also a good idea to have expert maintenance performed in the spring before your air conditioner’s duty increases for the summer (especially if your AC system is old).

A skilled HVAC professional will inspect your:

• Thermostat
• The fuse box
• Levels of refrigerant
• Compressor
• To keep your air conditioner from freezing, clean the coil.
• Clear the drain line on your air conditioner to keep it from leaking water.

Plus a lot more…

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.