Learn how AC leak sealer can damage your car’s AC

Understanding AC leak sealer and how it can harm your car’s AC system

Using an AC stop leak sealer in your car’s air conditioning (AC) system might seem like a quick and easy solution for fixing leaks, but it can cause more harm than good. Here are several reasons why you should never use an AC stop leak sealer in your car’s AC system.

AC stop leak sealer is not a new product. It’s been used in the natural gas industry for decades to seal small leaks on pipelines. The sealers are sold as just a leak sealer or as a combination leak sealer and seal conditioner. It’s also included in many AC recharge kits as an added selling feature.

How AC leak sealer works

The product is injected into the AC system as a liquid or along with a refrigerant recharge kit. The leak sealer remains a liquid and circulates throughout the system until it reaches a leak area. As the refrigerant leaks out of the system, it creates a cold spot at the leak site. The cold spot causes moisture in the air to condense. The moisture then interacts with the sealer to form a hadr epoxy-like “scab”, sealing the leak.

Sounds good so far, right? Just wait. It’s not such a rosy picture

How AC leak sealer damages your AC system

Unfortunately, AC leak sealers can’t distinguish between moisture in the air at the leak site and moisture in your AC system. It’s important to understand that when an AC system leaks refrigerant, it also takes in air, along with any moisture in the air.

Some of that moisture is absorbed by the desiccant in the receiver/drier or accumulator. However, the desiccant isn’t designed to absorb moisture from a leak; it’s designed to absorb the very small amount of moisture in the hoses at the initial charge. So if you have a leak, and air gets in, that moisture will flow with the refrigerant.

When the moisture reaches the coldest part of the orifice tube or expansion valve, it will condense and interact with the leak sealer, forming a hard epoxy-like scab right in the expansion device. And THAT is where the problem arises, because it blocks the flow of refrigerant.

When AC stop leak sealer combines with moisture, it clogs the orifice tube, expansion valve, receiver drier and accumulator

Adding leak sealer to a “wet” system can cause far worse problems than the original leak.

This image shows a completely clogged expansion valve caused by adding a leak sealer to an AC system that contained moisture.

That’s why the instructions for the professional AC leak sealers require a complete system evacuation to dry out the system. Some even require a new receiver drier or accumulator before adding the sealer. If you just add AC sealer to a wet system, don’t be surprised when it makes things worse.

AC leak sealers reduce cooling performance

This one is a mixed bag. If the sealer works to seal small leaks in the condenser or evaporator, it automatically improves system performance. No leaks = better performance. But, since the leak sealer isn’t a refrigerant, it doesn’t provide any cooling effect as it travels through the orifice tube or expansion valve. In other words, if you evacuate the system to dry it out and then add leak sealer and refrigerant, the combination can reduce cooling by up to 7%.

AC leak sealers can’t seal many leaks

When the sealer interacts with moisture, it forms a hard seal. That’s great

Compressor shaft seal

for pinhole leaks in the evaporator or condenser. But it won’t stop leaks at seals around rotating parts or at rubber O-rings, hose fitting, or the compressor shaft seal—which, ironically, are the most common sources for leaks.

AC stop leak sealers cause other problems,

Here’s an exact quote from industry trade magazine MOTOR from its April 2003 issue

“Pinhole sealing is a valuable function. But there’s no evidence that stop leak will seal anything else with any reliability, whether it’s cracked welds or a bad compressor shaft seal, or even severe pinhole leakage from the evaporator. Because the sealer works by reacting with moisture in ambient air, it also can produce clumps that restrict refrigerant flow, if there’s enough moisture in the system. In addition, the seal sweller in some sealing products could distort some O-ring materials.”

Worse yet, manufacturers of refrigerant recycling machines are reporting problems with refrigerant recovery when a customer has used an AC leak sealer product in the system. The sealer can plug the solenoid

This image shows how leak sealer clogged the shop’s refrigerant recycling machine equipment. That’s why shops charge extra to remove refrigerant that’s been contaminated with leak sealer

valve in the recovery equipment and also damages the seals in the equipment. Recover machine manufacturers like Skye, RTI, Visteon, Ford, Delphi Harrison, Four Seasons, and NAPA will void the warranty on the equipment if they find any evidence of an AC leak sealer.

Recovery machine manufacturers respond to the problems

To prevent damage to the machines, shops must install a separator/filter to prevent the leak sealer from entering the recovery equipment. The filters remove sealer clumps, oil, dye, and seal swellers. These filters must be replaced on a regular basis to allow the recovery equipment to work properly. The increased replacement cycle is why shops charge extra to remove contaminated refrigerant from your car’s AC

Here’s what you can expect if you use an AC leak sealer

• The sealer will probably work for very small pinhole leaks in the evaporator or condenser
• It will not work for leaks at the compressor shaft seal or O-rings.
• It will clog the desiccant in the receiver drier or accumulator if the system contains moisture
• It will reduce cooling by up to 7%
• If you ever take the vehicle to a repair shop, you will incur additional costs to evacuate the system because it is contaminated with sealer.

The most effective way to use AC leak sealer

To get the greatest benefit from a leak sealer, you must fully evacuate the system and replace the receiver/drier or accumulator. Then, pull a vacuum to remove any remaining moisture before refilling it with refrigerant and a leak sealer.

Or, evacuate the system and fix the leak, skipping leak sealer completely.

©, 2018 Rick Muscoplat