AC Compressor Noise At Idle: 4 Possible Reasons

If there is an AC compressor noise at idle in your car, you might be shocked: why would an AC make noises when clearly the car is shut off? Here are some reasons why this happens.

Whenever you turn AC on your car, you hear a noise from the vehicle. The noise is because of the compressor, a vital part of the air conditioning system.

The compressor is connected to the engine by a serpentine belt. When you turn on AC, the engine RPM increases because of the extra load on the engine.

The blower motor consistently produces cool air inside the car, so you hear noise from the vehicle.

AC compressor noise at idle is normal, but if you hear a rattling or humming sound, it is a matter of concern, and you need to take help from a professional to fix the issue.

AC Compressor Noise At Idle 4 Possible Reasons

Also read – AC Pro Gauge Not Working? Have you checked these reasons?

What Is An AC Compressor?

You simply turn your car AC whenever you feel hot while driving and get cool, refreshed air from the vents. The moment you turn on the AC, you activate the compressor. So, do you know about the working of AC compressors? Well, many car owners and occupants inside the car are unaware of the function of the compressor. Let’s discuss it in detail.

The compressor helps compress the refrigerant, i.e., it helps in increasing the temperature and pressure of the refrigerant. It then enters into the condenser, where the refrigerant is condensed into liquid form. But there will be no change in pressure and temperature in this case.

Next, the refrigerant passes into the expansion valve, where its temperature is reduced drastically. Now the refrigerant passes into the evaporator, which is a heat exchanger. The refrigerant exchanges heat with the warm air inside the car cabin; thus, the blower blows cold air.

Remember, turning on the AC puts a lot of load on the engine, so it is normal for the compressor to produce noise. But if it produces some strange loud noise, there is something wrong with your car.

Also read – what should you do if you find that air only blows through defrost vents

Different Types of AC Compressor Noise At Idle

The compressor is an essential component of the car air conditioning system. Its primary work is to compress the refrigerant at low pressure and low temperature to high pressure and high temperature.

There are numerous types of air compressor noise at idle conditions, like whirring, rattling, squealing, humming, and loud whining.

You don’t need to worry if you hear whirring noise from the AC compressor when the car is idle. But if you hear other noises like humming, squealing, rattling, or a loud whining sound from the Ac compressor, then it is something unusual, and you need to take your vehicle to the mechanic.

AC Compressor Noise At Idle 4 Possible Reasons

What Are The Different Types of Noises An AC Compressor Makes?

#1. Whirring Noise

The whirring sound from the AC compressor during idle conditions is normal. The noise comes because the engine motor and fan are working together. Although the sound is normal, every car owner must consider the whirring sound.

If the noise becomes louder, there must be an issue with the car’s mechanical components, which is a matter of concern. There can be issues with the blower, fan, or outdoor unit.

Sometimes paper or any derbies gets stuck inside the fan and causes such loud whirring noise. You can fix the issue easily by removing paper or debris from the fan. But if the fan and blower are not functioning properly, then take the vehicle to the nearest mechanic. Replace these parts if they are poorly damaged to resolve the problem.

#2. Rattling Noise

A rattling noise is the next compressor noise you may hear when the car is idle. It seems as if something is rubbing against the compressor. There can be numerous reasons for it.

Low or less oil on the compressor shaft can be the reason for producing noise. So, try to lubricate the shaft from time to time.

Also, loose bolts and screws are another reason you may hear a rattling sound. Try to supervise all the bolts and screws of the compressor. If you find them loose, then tighten them.

The next reason can be because of the worn serpentine belt. The compressor connects to the engine by belt. The life span of the belt is usually 100,000 miles. It has to bear constant stress and tension every time you operate the car AC; hence, it can get damaged in time.

Check the serpentine belt, and if you find it damaged, then it’s better to replace it with a new one.

AC Compressor Noise At Idle 4 Possible Reasons

#3. Loud Whining Noise

If you hear a loud whining noise, it can be because of two reasons, i.e., bad bearings or a damaged serpentine belt.

The bearings can get damaged with time; hence, inspect all the bearings if you hear such a sound. If you find any of them damaged, then it’s better to replace them.

The next reason is the serpentine belt. The belt is quite a simple component of Ac, but it serves the primary function. It helps connect the AC compressor clutch to the crankshaft; thus, the compressor runs by the engine power supply.

The belt can become contaminated with water or oil, hence not effectively producing loud whining noise. Additionally, it can become damaged with time and can have more grip on the pulleys. There can be cracks on the belt because of bearing constant heat, stress, and temperature fluctuation. Hence it cannot work effectively.

Sometimes it slips off from the pulleys because of excess damage. It can be the reason why you hear such a loud whining noise.

Remember, the compressor will stop working if the AC belt does not work. Hence the air conditioner will stop providing cool air inside the car cabin. Additionally damaged belt is not good for the car engine.

Inspect the belt as soon as you hear such noise. If you find the belt damaged, replace it with a new one.

AC Compressor Noise At Idle 4 Possible Reasons

#4. Humming And Squealing Noise

Humming noise is another noise from the AC compressor when the car is idle. There can be mainly two reasons behind it: refrigerant lines and loose components.

If the nuts, bolts, and screws become loose or not lubricated enough, then you are going to hear this noise from the compressor. So inspect the parts and if you find them loose, then tighten them. You can even lubricate the oil to avoid friction and such irritating noise.

Again, if excess or low refrigerant flows through the pipes, you will hear such noise.

The squealing noise can be because of AC compressor electric motor windings, fans, and blowers. Damaged fan blades can b the reason for producing such noise.

Similarly, malfunctioning of the blower housing and blower can be the reason. The motor windings can also get worn out with time. So, inspect the blower, fan, and windings once you hear such noise, and if required, replace them.

Frequently Answered Questions

#1. What does a bad air compressor sound like

When there are some issues in the air compressor, it will produce below noise that needs to be addressed immediately.

  • Rattling noise

This noise is produced when internal parts inside the compressor get loose with time. For instance, the motor is moving inside the sealed compressor because it has become loose and is producing a rattling sound.

  • Hissing or Humming sound

It indicates refrigerant is leaking from the pipes to the environment.

  • Banging or clanking noise

This noise is produced when loose parts are inside the compressor, like the piston pin and connecting rod.

AC Compressor Noise At Idle 4 Possible Reasons

#2. How do I stop my AC compressor from making noise?

Sometimes you hear AC compressor noise when debris like paper gets attached to the blower. It can be easily solved by removing the paper. But if the problem is severe, like loose parts inside the compressor or a worn-out belt causing loud sounds, you need to take the help of a professional.

#3. Why does my car idle loudly when AC is on

If the car AC is making a louder sound in idling conditions, there can be several reasons. For instance, the blades can get damaged with time, producing a loud sound. There can also be faulty air conditioner control valves.

The word of the air conditioner control valve is to allow a minimum amount of air to bypass the throttle body. But when it becomes faulty, it will enable more air to bypass, putting extra load on the engine. Hence the car idle becomes loud when you turn the AC.

#4. Will the AC compressor make noise if low on Freon?

Yes AC compressor makes noise when low refrigerant (Freon) passes through the pipes. It indicates that the refrigerant is leaking somewhere from the pipe to the surrounding, which is dangerous. The air conditioner cannot produce enough cooling effect, and you hear a bubbling or humming sound from the AC. Try to take the help of a professional immediately after hearing such a sound.

Wrap Up

The AC compressor is essential in providing cool air inside the cabin. But the piston rod, connecting rod, or serpentine belt can become loose or damaged with time and produce irritating noise when the car is idle. Take the help of a mechanic as soon as you hear such a loud sound from the compressor.

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Sean Mendez

Hi, I am Sean, a self-confessed petrolhead. I live in Boise, Idaho with a busy family of four and our energetic Labrador retriever. Thank you for visiting my website. You can find my email on the contact page.

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