Car AC Making Hissing Noise – Causes and Fixes

Is it normal for car AC to make noise? You don’t expect your home or car AC system to be quiet. Air conditioning systems make noise as they are running, but some noise will call your attention to malfunctioning components. One of the easiest ways to determine a fault in your air conditioner is to listen to how it runs.

One noise that signifies issues within the AC unit is the hissing noise. Do not ignore this noise. The probable causes of a hissing noise are internal valve leaks, leaky refrigerant lines, worn-out AC clutch, and faulty compressors.

If the hissing is emitting from the air vents, consider inspecting the air ducts for leaks. Hissing sounds are annoying and unnerving but don’t pose a catastrophic danger to the AC units. However, repair it before it escalates to a more serious issue.

In this article, we’ll discuss the causes of car AC making a hissing noise. We’ll outline some repair procedures on how to fix the hissing sound in a car AC.

car ac making hissing noise and not cooling

Why Is the Air Conditioner of Your Car Making A Hissing Noise?

If you think hissing sounds are likely signs of a refrigerant leak, faulty compressor, and leaky ductworks, it’s not always the case. If the hissing sound is evidence only when your AC unit is active, it is emitting from the ductworks. That said, car AC making noise from vents is a minor issue.

It’s not a severe problem to warrant your attention and may not escalate. So, if the noise doesn’t irritate or embarrass you, ignore it.

If the hissing noise is emitting from the AC unit itself, there’s a much bigger problem that needs urgent attention. Do not ignore it for an extended period. It can cause severe system damage and drop expensive repair bills on the table.

The air conditioner hissing when off and on shows, there’s a refrigerant leak on the lines or fittings. A refrigerant is a gas that is used in the air conditioning system to expel heat from the surrounding air. It helps in sending icy air into the cabin.

Some experts call refrigerants, Freon. This is just a brand name that produces refrigerants. You can check out this article that compares Freon vs refrigerant.

Indeed, hissing means there’s a leak somewhere around the system. Sometimes it can emit from the internal AC valves. This type of issue can quickly affect the smooth running of the compressor.

The compressor is one of the major and most expensive AC components. For this reason, it is important to seek professional help whenever you notice hissing sounds.

As alluded above, a hissing sound shows a refrigerant leak, but if a shrieking and screeching sound accompanies the hiss, you have compressor issues. A faulty AC compressor and defective clutch are some reasons car AC makes a hissing sound when turned on.

If you switch on your Ac unit with a lousy compressor, it’ll cause catastrophic system damage over time. The repair cost will go uphill. Immediate attention is all you need to keep enjoying your ride.

Ways to Fix Hissing Sound in Car AC

As explained above, hissing noise can be caused by either refrigerant leaks, internal leaks, or a faulty compressor. So fixing hissing sound may require different approaches since there are various causes.

Refrigerant line leaks

If you find a refrigerant line leaks on the evaporator or condenser, repair or replace the entire faulty unit. To repair it, cut and crimp the tubes to seal the pinhole cracks. Of course, you can choose to solder the punctures on the tubes. The choice is yours.

In any case, if you discover a bigger hole, you’ll need to contact an expert HVAC technician to repair it. Such work requires professional help.

If the refrigerant leak is coming from along the refrigerant lines, you will need an AC repair seal to fix the leaks. It is a pretty easy and inexpensive way of fixing leaks along refrigerant lines.

AC repair seals can also fix leaks on air conditioner metal components and remove accumulated moisture from the system. These conditioners and seals also seal leaks on rubber materials.

Here are the procedures you should follow to fix the hissing noise caused by refrigerant leaks.

  • Find the low-pressure line service port of the refrigerant lines. It is a bigger aluminum pipe that connects to the compressor and goes to the firewall.
  • Take off the valve handle on the refrigerant recharging hose.
  • Gently attach the AC repair seal can. Ensure that it is snugged properly before moving to the next step.
  • Start the vehicle and switch the AC and fan to max or high settings.
  • Fix the hose coupler end onto the low line port.
  • Pierce the recharging can by turning the valve on it clockwise.
  • Turn the valve in the opposite direction to inject the AC repair seal into the refrigerant.
  • Turn the can and hold it upside-down until the seal empties into the refrigerant.
  • Disconnect the hose and take off the can.
  • Check the refrigerant pressure and add more if necessary.
  • Cover the recharging port with the cap you removed earlier. Start the engine and allow it to idle for 25 to 35 minutes.

This exercise is to allow the supper seal to mix properly with the refrigerant and seal the leaks. The hissing sound should be gone and you now have icy feelings inside the cabin.

Internal leaks

Hissing because of leaky internal valves will start slowly and intensify with time. If you observe this, diagnose the AC system ASAP before it escalates to a more serious issue.

Remember, the compressor valve controls Freon pressurization. So, if the Freon is not pressurized, the system will not produce cool air.

Replacing a leaky valve is pretty easy. Anyone can do it. Suppose the refrigerant leak is emitting from the high-pressure line, you’ll have to discharge the refrigerant first. This is because the high-pressure line does not have a Schrader valve. Instead, it uses a ball-type valve.

You’ll need the proper equipment to evacuate the refrigerant. If the proper equipment is not in your garage, you need to visit a nearby auto garage.

Here are the steps needed to replace a leaking internal valve.

  • Locate the low-pressure line and take off faulty the Schrader valve. You’ll have to get a stem valve remover to carry out this work properly.
  • Insert a new Schrader valve.
  • Ensure there’s no air in the system
  • Recharge the AC unit until it gets to the required PSI.
  • Determine if the air conditioner is giving icy air via the air vents.

Compressor issues

Other causes of air conditioner hissing sounds are compressor problems. It could be you have a defective AC clutch or a lousy compressor. Hissing sound from car AC when accelerating shows you have a faulty compressor idler pulley or clutch.

Repairing or replacing the faulty component will resolve the problem. Of course, you’ll recharge the AC refrigerant.

how to quiet a noisy car ac compressor


Q: Why is my air conditioner making a whistling noise?

A continuous whistling sound is an obvious sign of a refrigerant leak, which can lead to low Freon in no time. As alluded above, refrigerant leaks can come from internal valves or refrigerant lines.

Refrigerant leaks can give hissing, whistling, and bubbling sounds. Leaky internal valves will escalate if ignored for an extended period. Diagnose and fix any leak in the system if you want icy air into your cabin.

Q: Is it normal for car AC to make noise?

It is pretty normal for a car AC to make noise. However, some noise projects an underlying problem in the system units.

Noises like rattling, hissing, knocking, clicking, squealing, screeching, and buzzing signify a system problem from one component or the other.

Q: How do I stop my AC from whistling?

Did you hear a high-pitched whistling noise when you switched on your air conditioning system emitting from the air vents? It is most likely caused by limited airflow. It means enough air is not getting into the vents. Whatever the reasons are, you want to stop it.

Stopping AC from whistling is super-easy. It requires cleaning or replacing dirty air filters. As the name implies, air filters prevent dust and dirt from getting into the cabin. Over time, the filtered dirt and dust will clog the system and cause restricted airflows.

You need to unclog the air vents. The air vents do similar work with air filters. They should be clean from dirt and dust.

Q: Can I drive with a hissing noise?

Hissing noise shows several issues exist in a vehicle. It could be exhaust leaks, faulty AC valves, or air conditioning system issues like refrigerant leaks. Depending on the cause of the noise and when it started, it can mean several problems.

While a hissing sound may not stop you from driving your car, the AC system may not function. In addition, if a defective AC clutch is the culprit, it can cut the serpentine belt and affect other belt-driven components.

If this happens, it can lead to catastrophic damage to the power steering system, charging system, etc. It can even result in engine overheating.

Q: How much does it cost to fix the hissing noise?

The first step in stopping a system leak is to determine where the leak is coming from. If you consult an expert HVAC technician to run the inspection, it’ll cost you around 100 to 300 dollars. This includes checking the connections, drive belts, hoses, and recharging the system.

Fixing and replacing faulty system components like lousy condenser and compressor will be around 100 to 800 dollars. This also involves recharging the AC refrigerant.

Final words

This article has provided sufficient information on the causes of car AC making a hissing sound. It has also provided a simplified guide on how to fix the hissing sound of car AC.

If you have a hissing sound on your car AC, first diagnose the AC systems and follow the above instructions to fix it.

If you don’t have the tools or don’t trust your guts, visit a professional HVAC technician. They have all the tools to fix the problems professionally.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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