4 Causes of Hissing Sound after Recharging AC

Sounds are natural in vehicles due to the numerous working components. The air conditioner also makes noise as the HVAC system runs. However, some sounds are signs that something could be wrong with one or more components within the AC.

If you hear a hissing sound after recharging AC, the air conditioner has a refrigerant leak. The sound is a sign that the HVAC system is losing pressure due to escaping refrigerant. The leaks usually appear under the hood around the AC compressor, within the cabin, or under the vehicle.

Some of the probable causes of such a hissing noise are leaky refrigerant lines, internal valve leaks, overcharging, and a defective compressor. Inasmuch as these faults may not directly impact your vehicle’s drivability, do not ignore them.

In this article, we’ll look in-depth into the causes of the hissing sound from car AC after recharge and the step-by-step procedure on how to fix the problem ASAP.

hissing sound from car ac

Reasons of Hissing Sound after Recharging AC

Several potential issues may be responsible for producing a hissing sound after recharging a car’s air conditioning system. However, these causes vary depending on the specific circumstances and condition of the AC system. Here are some common causes of the hissing sound coming from your car AC.

#1. Leaky refrigerant lines

Refrigerant leak is the chief of all the causes of a hissing noise from car AC after a recharge. Leaky refrigerant lines are the major culprits in this case.

If you consistently hear a hissing noise coming from your AC after refrigerant recharge, ensure to check the refrigerant lines for any damage. A refrigerant leak can lead to poor AC cooling performance and potential damage to the compressor if left unchecked.

#2. Overcharging the AC 

Overcharging the air conditioning system with refrigerant can also cause a hissing sound. When the AC system is overfilled with too much Freon, excessive pressure can build up within. This can cause refrigerant to escape via relief valves or other weak points in the HVAC system, resulting in a hissing noise.

Meanwhile, it is important to avoid these two extremes – overfilling your air conditioning system or running low on refrigerant. You can gradually damage your air conditioning system through any of these.

#3. Internal leaks

Loose/faulty connections or damaged seals can result in internal leaks in the AC system. This can further trigger a hissing noise from car AC. Meanwhile, it is important to state that vibrations and regular wear can result in ac recharge hose loose connections and damaged seals.

Since the air conditioning system is pressurized, any slight opening caused by a loose connection or broken seal can possibly trigger a hissing noise. Failure to fix this as soon as possible can cause a more severe problem to the AC.

#4. Faulty compressor

The HVAC system consists of vital components that work in synergy. If the compressor, expansion valve, or pressure relief valve gets damaged, they can contribute to generating a hissing sound after recharging the AC.

If your car AC makes hissing noise when turned on, these faulty components may be directly responsible for the sound. On the other hand, they can also contribute to abnormal pressure levels in the system, leading to leaks and, thus the hissing noise.

How to Fix Hissing Sound in Car AC

Ignoring any minor AC malfunction is an invitation for more severe problems. Therefore, if you’re battling a hissing sound after recharging your AC, the following procedure will help you fix the problem ASAP.

Fixing Car AC Hissing Noise YouTube

Diagnose the actual cause

Assuming a cause and fixing any random component without any clarity is not a wise thing to do. Hence, you must carefully diagnose the hissing air conditioning system to ascertain the exact cause of the problem. If you’re not an experienced DIYer, you may need to contact a professional auto technician for this job.

Repair leaky refrigerant lines

If you identified one or more leaky refrigerant lines as the cause of the hissing noise, ensure to repair or replace them immediately. The components are relatively cheaper compared to some other sophisticated AC parts.

Replace damaged seal

If you have a damaged seal, kindly get a new replacement immediately. Also, ensure to tighten all loose connections in the air conditioning system. This may be all you need to do in some circumstances.

Replace faulty AC components

Lastly, a damaged compressor will definitely affect the entire AC system. So, if you have a malfunctioning compressor or expansion valve, kindly repair/replace the components ASAP.

However, a compressor can be pretty expensive. Nevertheless, your car’s AC can be completely grounded due to a damaged compressor. So, ensure to repair the component if the fault is relatively minor; otherwise, you may be in for a whole new replacement.

Some of the repairs or replacement parts above can be pretty costly. However, you can easily avoid labor costs if you’re a DIYer. In any case, it is recommended to have a professional technician diagnose the issue if a hissing sound occurs in your car after AC recharge.

This kind of repair requires some expertise. Also, you may not have the tools necessary to identify the specific cause and provide appropriate solutions to resolve the problem effectively. 


How long does an AC recharge last with a leak?

The refrigerant in a recharged AC will only last a few weeks to a few months with a leak. However, the speed of exhaustion depends on the severity of the leak. If there is more than one leaking spot in the AC, the refrigerant may be exhausted sooner than expected.

So, it would be best to respond swiftly to a refrigerant leak issue. This will help you prevent wastage and other secondary AC problems associated with refrigerant leaks.

Is it normal for AC compressor to make noise?

A car’s AC compressor works quietly under normal circumstances. Hence, if the component starts producing humming, clanking, buzzing, or rattling noise, it’s simply a sign of malfunction.

The air conditioner compressor is the heart of the HVAC system. The component is also the most expensive to replace in the system. Therefore, it’s vital to rectify any suspected malfunctions immediately before they escalate.

Is it OK to run AC without refrigerant?

A vehicle’s air conditioning system cannot function without refrigerant. However, the system can run with a low refrigerant level. Nevertheless, this will impact the air conditioner’s efficiency to a large extent.

Always ensure to maintain the recommended refrigerant level for your AC. Low refrigerant level comes with a lot of inconveniences. What more? You could cause serious damage to your AC if you fail to always keep the recommended amount of refrigerant.

How much does it cost to fix ac hissing noise?

Fixing your air conditioner’s hissing noise costs around $100 – $300. This cost covers the checking of hoses, connections, and refilling of the refrigerant.

Furthermore, you may spend around $100 – $800 if you need to replace some faulty components. Fixing an AC problem can be somewhat tricky. Therefore, it would be best to contact an expert to do the job.


Generally, most vehicle components make noise when running. However, a hissing sound after recharging AC is abnormal. In other words, ensure to check it out as soon as possible. Such a situation may appear to be insignificant.

However, a tiny leak in the air conditioning system can degenerate into a more severe problem. From just having a hissing sound, you could experience poor AC cooling. Other faults may be triggered if you fail to check for the main cause of the hissing noise.

Meanwhile, your car’s air conditioning system is a delicate component, especially the compressor. That being said, kindly ensure to consult a professional auto technician to handle repairs related to the HVAC system.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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