AC stop leak — Why you should never use it in your car

AC stop leak products rarely work and contaminate your system

Many DIY recharge kits contain an AC leak sealer stop leak additive. Unfortunately, those leak sealers rarely work. But worse than that, they contaminate your AC system, increasing the cost of repair if you then take it to a shop.

Due to all the DIY kits with AC stop leak and the substitute refrigerants, shops always test the refrigerant before working on a vehicle. If you’ve added an AC leak sealer or stop leak, you’ll have to pay a hefty upcharge for the shop to evacuate and dispose of the contaminated refrigerant because it cannot be recovered using their regular shop equipment.

Why AC stop leak products don’t work

Some AC stop leak manufacturers claim their products will seal leaks in rubber hose connections and O-ring seals or a combination metal rubber gasket. However, since rubber components flex and the sealer additive forms a rigid patch, any movement will break the seal and the system will leak again. Also, stop leak products never work on a leaking compressor shaft seal because it’s rotating component.

The few instances where AC leak sealer might work

AC leak sealer works when it comes in contact with moisture in the air. If you have a pinhole leak in aluminum tubing like the condenser, evaporator or accumulator/receiver-drier, the stop leak product might work. The moisture causes the sealer to harden, so it “scabs” over the leak.

But just as it hardens with moisture in the air, it can also harden with moisture and air in your car’s AC system, which is what happens when the system has a leak. Refrigerant not only leaks out, but moisture and air get in. So the stop leak product can harden in the system

Can AC sealers harm your AC system?

As I said above, the sealers work by reacting with moisture to form a hard patch. If you’re a DIYer and using an AC recharging kit with AC sealer or contemplating adding a can of AC sealer, consider this:

Since your system is low on refrigerant, that automatically means you have air in the system and that air contains moisture. The desiccant in the accumulator or receiver/dryer is designed to absorb some of that moisture, but there’s a limit to how much it can hold. If your system any remaining moisture circulating in the system, it will react with the AC sealer and harden. That can plug up the orifice tube or your expansion valve.

Clogged expansion valve

©, 2020 Rick Muscoplat