Air Conditioners | 7 Min.

Why Is My Air Conditioner Making a High Pitch Whistle?

Written by Chris

Your AC system can break at some point, producing a high-pitched whistle sound that is so irritant to the ears. This happens when the air conditioner system has a low return flow of air.

It means that the air conditioner is not getting enough air through vents. Various conditions and factors contribute to the air conditioner high pitched whistle. This article lists the five most common causes.

Why is Your AC Making that High Pitched Whistle?

A high-pitched whistling sound coming from the air conditioner means that there is not much airflow going through the vents and ductwork. So the Air conditioner puts more effort to pull enough air into the system making that whistle noise.

Cause 1: Dirty Air Filters causing the whistle noise

The air filters are designed to filter unwanted particles and dust from getting into the air conditioner. If dust is in the air conditioner’s system, proper functioning might have some challenges. When these air filters become dirty, they restrict the airflow, causing overheating.

As a result, the air conditioner will make a high-pitched sound due to airflow resistance. You can try cleaning the air filters by yourself so it gets enough airflow. This one is probably relatively easy to deal with. However, it can be quite challenging to unclog an air conditioner that has a complex structure.

Cause 2: Blocked Return Vents

blocked returning vent making whistle noise in ac

Blocked return vents are the massive vents mostly located in hallways and other open areas. If anything is blocking them, then a proper function of the ducts is not possible. Things such as heavy dust and furniture might create some interference and affect the process in which the air gets in. The supply vents help the AC get airflow into the system, maintaining the airflow. The only solution to this is the removal of any blockages and ensuring all the supply vents are open all the time.

Cause 3: Closed Dampers leading to the whistle sound

closed and open damp

These are metal valves located in the ductwork and are used to prevent air delivery to specific parts of the building. The only possible solution for this issue is to put your unit on the inside of the room ensuring proper alignment with the ductwork. This is important to get more airflow to the AC system.

In a room where there are too many closed doors, the air supply is affected. If there is minimal airflow in the room, the blower will have to work harder and pull more air. This process of overworking the blower will automatically create the whistling noise experienced by the AC. The possible solution is to ensure that the room is well ventilated to increase airflow.

Cause 4: Copper lines rubbing against each other

Need for alarm? No. When the copper lines outside or inside start rubbing against each other, it produces a loud screeching noise. It could be an issue with the thermostat. When you experience this issue, you will need to change a condenser coil or an air filter.

However, this problem would require some keen scrutiny as it could be a little challenging to discover. People often think the issue is more significant than it is, while it could just be some minor problem.

Cause 5: Refrigerant Leaks

refrigerant making ac whistle noise

If you hear loud rattling whistle noise after switching on the air conditioner – chances are that it’s a refrigerant leak. Refrigerant leaks can be another reason for the air conditioner’s high-pitched whistle. It could be due to increased internal pressure inside your compressor.

This could be very dangerous, so it’s better to call a professional HVAC technician. When this happens, it is highly advisable to switch off the whole AC central power station. If left as it is, it could cause damage. Unfortunately, this problem could only mean one thing the system has come of age and needs to be replaced. It is because continued use could one day result in major malfunctioning.


Those are some of the common factors that can contribute to the malfunctioning of the air conditioner system. Most of the problems are airflow-related problems. With an increasing number of households using ACs, it is essential to be aware of this. The good news is that a little over ninety percent of these issues that cause whistling sounds can be fixed. It is therefore recommended not to panic when you notice such issues. Call an expert to repair your AC system.

If you are facing issues with your AC, Smile HVAC will help you repair your AC in Toronto.