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Car AC Hissing and Not Cold: 6 Reasons and Solutions Listed

If you are a car owner, you have probably encountered the problem of your car AC hissing and not cold. Luckily, you’ve found the right place to help you fix this malady. I will outline some of the causes of this issue and give you clear remedies.

Without further ado, let’s get into it straight away!

Car AC Hissing and Not Cold: 6 Common Reasons

Your AC’s production of a hissing noise can stem from multiple reasons. While sometimes it could simply be the AC acting up, it could indicate a key problem in some instances.

Let us review these instigators!

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1. Moving the Refrigerant Gas in the Expansion Valve

In any car AC, there is always a refrigerant. This gas is responsible for creating the cold air. As this gas travels through the unit and valves, it may make a hissing noise. This occurrence happens often and shouldn’t startle you because, after a while, it dies down.

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However, in some instances, the problem could be the air filters:

  • In an AC, the air filters prevent dust from accessing integral parts of the unit.
  • If you let this dust and debris pile up over a long period, they obstruct airflow.
  • This feature births the hissing sound when freon moves across the AC system.

2. Refrigerant Leaks in Your AC

Another reason you may hear the hissing sound on your vehicle’s AC is if the refrigerant is leaking. The easiest way to notice a refrigerant leak is a failure in the cooling system. It could leak at any point in the AC, rendering it unable to absorb and dissipate heat correctly.

Refrigerant leaks could result from several reasons, including:

  • Wear and tear of refrigerant lines: These passages conduct the coolant throughout the air conditioner.
  • Broken seals: These breakages could happen in several areas in the AC unit.
  • Schrader valve leaks: These valves are the designated places to measure the pressure for most air conditioners. They also serve as the coolant refilling point. Leaks are likely to occur at this spot.

3. Issues With the Condenser Fan Motor

The condenser is vital in dissipating heat from the refrigerant in your car AC. When faulty, it results in several issues, including:

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  • Reduced efficiency in the cooling process: The condenser’s primary function is blowing air over the coils, compromising hot, high-pressure freon. This process aids in liberating heat from the coolant to the environment. A fault in the condenser disrupts the whole process.
  • Pressure builds up in your AC: This build-up stems from the refrigerant leaving the condenser, becoming hotter and at a higher-than-average pressure.

In some instances, there could be debris piled up, restricting airflow. The hissing noise thereby results from the air trying to escape.

4. Occurrence of an Overcharged System

Overcharging occurs when the AC system is overloaded with refrigerant. When this phenomenon occurs, your compressor is forced to work double time, which may lead to its malfunction due to the pressure build-up. If this problem causes the hissing sound, it’s because the gas is trying to escape.

Furthermore, the system overcharging may lead to:

  • Excessive evaporator coil cooling;
  • Creating ice or frost.

Important! If left unattended, this ice may damage the coil and obstruct air flow, resulting in reduced cooling.

5. Leaking of the Internal Valve

Internal valves are crucial to pressurize the freon in your car AC system. Just like tire valves, leaks experienced in this part can be simply fixed. However, this doesn’t mean you should take it lightly. Ignoring it may result in multiple casualties for your AC. Some include:

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  • Inefficient cooling: It results from the loss of coolant.
  • System inefficiency: Due to the refrigerant leak, the AC will use more energy. In your vehicle, this feature will be reflected in our fuel consumption, which will be proportionately increased
  • Compressor mutilation: When there is a refrigerant leak, the compressor works more. While it can put up for a while, it is eventually at risk of failure. Replacing compressors is also expensive.

6. Compressor Faults

Most drivers know that the compressor is the most costly part to replace in an AC unit. This component pressurizes the freon and distributes it throughout the AC system. Most often, when the compressor is damaged, it results from the high pressure built-up. However, other causes include:

  • Used-up seals: Once worn out, these seals can no longer serve as barriers. They begin letting out the coolant gradually.
  • Broken valves: Through them, the coolant can escape.
  • Mechanical failure: Sometimes, your AC may fail as all appliances are subject to error.

The Major Reason Behind a Hissing Noise When You Turn Off Your Car

If, at one point, you were halting your vehicle, powered down, and noticed a hissing sound that alarmed you, I am pleased to inform you that you shouldn’t be startled. When you hear this noise, it simply indicates that your AC is balancing the pressure.

Your car’s AC system is separated into:

  • The low-pressure side;
  • The high-pressure side.
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The coolant travels through the tubes and shifts from each side when functional. Often, you’ll discover that one side bears more gas than the other. The hissing sound thereby results from gas in the high-pressure side flowing into the low-pressure compartment.

Other Factors Causing a Hissing Sound from Car AC

There are multiple reasons that can prompt your vehicle to give off a hissing sound. While some of them are no cause for alarm, you should not ignore others. They constitute the following:

  • Extreme pressure builds up in the system: In this instance, the air conditioner will respond by letting off some steam, which is where the hissing noise results.
  • Leaks in the system: If you experience an inefficient supply of cool air, this is most likely an outcome of the freon leak. During its breakout, you’ll encounter the hissing nose.
  • Inadequate refrigerant: When left unused for a bit, your car’s air conditioner may let off some hissing noise due to the leaked refrigerant. Think of it as the hunger cue for the air conditioning unit.
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Guide to Fixing a Hissing Car Air Conditioner

Depending on the magnitude of the cause, correcting the features that cause a hissing noise isn’t that much of a hassle. Let’s review these steps.

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1. Search for Refrigerant Leaks and Low Refrigerant Levels

The first step in solving any malady is identifying what is the cause. Searching for leaks and diminished refrigerant levels is a good place to start. As mentioned above, losing the coolant renders your AC unit ineffective.

Before beginning this process, make sure that you have protective gear on. You can visually inspect the car’s air conditioner to spot any leaks. As you can’t see, there are other ways to identify leaks, including:

  • Using a pressure gauge: Fix the appliance to the low service pressure point and note the measurements.
  • Electronic leak detector: This sensitive gadget can detect freon leaks in the atmosphere. Move it around the air conditioner to locate the obstacle source.
  • UV dye inspection: Introduce the dye to the air conditioner through the low-pressure service port. Turn on the engine and let the AC run for a short while. After this, use a UV light to identify the source of the leaks.

2. Review and Clean the Air Conditioning System Elements

After continued usage, your car’s air conditioner will likely acquire a lot of dust and dirt. This phenomenon can clog various appliances, including:

  • Air filters;
  • Condensers;
  • Evaporators.

This problem makes it harder for your air conditioner to blow cold air, resulting in the hissing noise.

Clean all these parts using compressed air and their passages, like the expansion valve, to make it easier to pass air. Furthermore, clean your air filters. AC gadgets free of obstruction allow the air conditioner to pass cool air easily.

Note: If the filters are worn out, the most preferred solution is to replace them.

3. Assess and Fix All the Damaged AC System Parts

In some instances, the air conditioner hissing sound can be traced back to particular elements like the compressor or expansion valve. Fixing these parts may need an expert opinion. Messing around with delicate and vital components can result in more damage than good.

Contact your car dealer or a qualified professional to fix the hissing sound by tinkering with these parts.

Price of Fixing the Hissing Noise in Car AC

The price of repairing a car AC to ensure it is blowing cold air regularly will vary based on what component is faulty:

  • Visiting your mechanic will force you to cough up at least $100 to diagnose the issue.
  • If the parts demanding repair are minor, like Schrader valves, the furthest, it can go up to $800.
  • However, if the issue is more serious, like substituting the compressor, you’ll have to pay a few thousand bucks.
Important! It is essential to note that sometimes, repairing one part after the other is costly in the long run. It is better to replace the entire AC unit.


Why Is My Car AC Blowing Air but Not Cooling?

Your car AC is blowing air but not cooling because the refrigerant levels are likey low. Furthermore, your car’s air conditioning system could be dispelling freon through damaged leaks.

Can Low Freon Cause Hissing Noise?

Yes, low freon can cause hissing noises. This observation happens since, in most instances, the car hasn’t been in use, and the coolant has been and is still leaking, making it cause a hissing noise.

How Do I Stop My AC From Whistling?

You can stop your AC from whistling by substituting the cabin air filter. Additionally, you can inspect for obstructions and clear them.

What Does a Bad AC Compressor Sound Like in a Car?

Abad AC compressor may produce several annoying sounds in a car. The most obvious one, however, is a high-pitched squealing or screeching sound.


That’s all we rounded up regarding your car AC hissing even when it’s not cold. This occurrence is no stranger to most drivers. While in some instances, like when the pressure is equalizing, it is not alarming, it can indicate serious issues sometimes.

Some reasons behind the hissing sound in your car air conditioner include issues with the condenser fan motor, internal valve leaks, refrigerant leaks, overcharged system and compressor problems. To fix these issues, start by inspecting the problem cause and then cleaning out the debris. If there are any faulty components, replace them.

So, have you encountered any issues with your car air conditioner regarding the hissing sound? Notify us in the comment section below.

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