Auto AC stop leak — Why you should never use it
Why Using AC Stop Leak Can Cause More Harm Than Good
When the AC system starts to malfunction, one of the most common causes is a refrigerant leak. To address this issue quickly and inexpensively, some people turn to auto AC stop leak products. These products are marketed as quick fixes that can seal minor leaks in the AC system without the need for expensive repairs. However, despite the convenience they promise, using an auto AC stop leak product can cause more harm than good. In this article, we will explore what Auto AC stop leak products are, how they work, and why you should avoid using them in your vehicle.
What Are Auto AC Stop Leak Products?
Auto AC stop leak products are chemical additives designed to seal small leaks in a vehicle’s air conditioning system. They are typically sold in cans and can be added directly to the AC system through the low-pressure service port. These products claim to seal leaks in the AC system’s hoses, seals, and other components by forming a chemical bond or by hardening when they come into contact with air or moisture.
How They’re Supposed To Work
The working mechanism of Auto AC stop leak products varies depending on the brand and formulation, but they generally operate in one of two ways:
• Sealing by Chemical Reaction With Outside Moisture— Some stop leak products contain chemicals that react with moisture and air to create a hard seal over leaks. The idea is that as the refrigerant and the stop leak chemical circulate through the AC system, the chemical will find the leak, leak out, react with outside moisture right at the leak site, and harden, effectively sealing the hole.
• Swelling of Seals— Other stop leak products work by causing the rubber seals within the AC system to swell, temporarily closing off any gaps or cracks. This method aims to restore the seal’s integrity and stop the leak.
Unfortunately, auto AC stop leak products damage AC refrigerant recovery machines
Due to all the DIY kits with auto AC stop leak and the substitute refrigerants, shops always test the refrigerant before working on a vehicle. If you’ve added refrigerant with an AC recharge kit that contains an AC stop leak additive, you’ll have to pay a hefty upcharge to the shop to evacuate and dispose of the contaminated refrigerant. Auto AC stop leak products clog up the filters in the recovery machines. Someone has to pay for those damaged filters and that someone is you.
The Dangers of Using Auto AC Stop Leak Products
While the idea of a quick and easy fix for an AC leak might sound appealing, there are several reasons why using an auto AC stop leak product can be detrimental to your vehicle’s AC system.
1) Potential Damage to the AC System Components— The chemical reaction type sealers are not selective in where they form seals. If your car’s AC is leaking refrigerant, chances are it also has air in the system and that air has moisture in it. The chemical reaction type sealant can react with the air an moisture and cause a clog wherever it finds the air and moisture.
For instance, the sealant might harden within the small passageways of the AC compressor, condenser, evaporator, or expansion valve, leading to clogs that disrupt the system’s operation. These clogs can reduce the efficiency of the AC system or, worse, cause component failures that require expensive repairs or replacements.

This DIY never expected the stop leak product in his recharge kit to react with moisture in the system to clog up the expansion valve. Now, instead of fixing just the leak, they have to also replace the expansion valve.
2. Risk of Contaminating the AC System— AC systems are designed to operate with a specific type and amount of refrigerant and oil. Introducing a foreign substance, like a stop-leak product, can contaminate the system. This contamination can result in poor lubrication, leading to increased wear and tear on the AC compressor and other components. Over time, this can cause a decrease in cooling performance and, eventually, system failure.
3. Incompatibility with Modern AC Systems— Modern automotive AC systems are more complex and sensitive than those of the past. They are designed to operate with specific refrigerants, such as the newer R-1234yf. Stop-leak products may not be compatible with these refrigerants or the materials used in modern AC systems, leading to unintended chemical reactions or damage to the system’s components.
4. Difficulty in Diagnosing and Repairing the AC System— Once a sealer product has been added to the system, diagnosing the original problem can become much more difficult for a professional technician. The stop leak product can mask the symptoms of the leak, making it harder to pinpoint the exact location and severity of the issue. Moreover, if the stop leak has caused blockages or contamination, additional steps may be required to clean or flush the system before any repairs can be made. This can lead to increased labor costs and longer repair times.
5. Voiding of Warranties— Many vehicle manufacturers and extended warranty providers explicitly state that the use of sealants in the AC system will void any remaining warranty coverage on the system. This is because these products are seen as a temporary and potentially damaging fix rather than a proper repair.
Why these products usually don’t work
Some AC stop leak manufacturers claim their products will seal leaks in rubber hose connections, O-ring seals, or a combination metal rubber gasket. However, since rubber components flex and the chemically reactive sealer additive forms a rigid patch, any movement will break the seal, and the system will leak again. Also, they never work on a leaking compressor shaft seal because it’s a rotating component. Lastly, all modern auto AC systems use HNBR O-rings that are highly resistant to seal swelling chemicals
©, 2020 Rick Muscoplat
Posted on by Rick Muscoplat