Photograph of attic air conditioning air handler, condensate drips on floor A/C - Heat Pump Refrigerant Leak Sealant Guide
Sources of leak sealants, refrigerant leak sealant procedures

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Sealants for air conditioning, heat pump or refrigerator / freezer refrigerant gas or liquid leaks:

This article describes the use of air conditioning and heat pump refrigeration system leak sealants: a canister or container of sealant, a mixture of gases and an active sealing product, is attached to and fed into the A/C or refrigeration system's low-pressure side where it flow to and seals small-diameter leaks in the refrigerant piping system, cooling coil or evaporator coil. Refrigerant leaks up to about 0.5mm can be sealed using this method.

Warnings about failure to follow the manufacturer's recommendations and about possible damage to the refrigeration equipment are included.

This article series discusses how to repair refrigerant leaks in air conditioning and cooling systems, using as an example, repairing a leaky or damaged air conditioning the cooling coil (evaporator coil) in the air conditioning air handler unit. Our photo at page top shows the cooling coil in the attic air handler component of a central air conditioning system.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Using an A/C or Refrigeration System Refrigerant Leak Sealer

AC system refrigerant access ports (C) Daniel Friedman

Reader Question: 20 July 2015, A/C issues-blowing warm air said:

My A/C unit is blowing warm air. The repairman added a pound of freon and recommended I add a stop leak additive to the system. I added it but the air still wasn't as cool as it should be.

He came back out, said I had "low head pressure" and may need new TXV if adding more freon didn't help.

It didn't, so I called him out to replace the TXV and he found the A-coil was extremely dirty. He cleaned it as well as he could with my vacuum and said He could cut it out, acid bathe it and reinstall for around $550 or I could try cleaning it myself with coil cleaner.

I opted to try it myself. After he left, I noticed the condensor fan outside only runs for about 15 minutes then shuts off.

[Click to enlarge any image]

I have to turn off the system and let it set for 30 minutes or so before trying again but it still shuts down. With the thermostat set to 73 degrees, it's running closer to 80 (I had to buy a window unit to survive our 100 degree days). Any ideas?

This question was originally posted at DIAGNOSTIC GUIDES A/C / HEAT PUMP



Although some HVACR repair contractors use leak-stop products in refrigeration systems, I'm not a fan of using a "stop leak" product inside refrigeration systems as am nervous about the prospect of the "stop leak" product clogging up the thermostatic expansion valve (TXV).

While I never encountered the problem myself, I've read claims by some HVACR techs that these products might damage a compressor - I'll say more about that below. According to ACHR News, Cliplight, a manufacturer of Super Seal refrigerant leak stop agent, says the products are tried and tested, help eliminate water from the system [sic], and contain a UV tracer dye to find largter leaks. (Rajecki 2016).

Watch out: That same article quotes from Danfoss, and from Emerson Climate Technologies, both large manufacturers of HVACR equipment, warning that

Without testing each of the leak additives, Danfoss cannot guarantee they won’t negatively impact the long-term reliability, so we will not endorse these type of additives. If detected during a warranty claim, it would void our warranty terms. - (Danfoss in Rajecki 2016)

The typical refrigeration or air conditioning system has multiple designed orifices with restriction from cap tubes and thermal expansion devices to injection ports and oil feed holes. Adding a substance intended only to block refrigerant leaks, thereby blocking the orifices, creates a host of potentially negative implications.

The substance also brings with it unknown effects on the system’s components, seals, oils, and even manufacturing process fluids over time. Because there are so many unknown effects at this time, Emerson does not approve the use of additives in the presence of refrigerants. - (Emerson in Rajecki 2016)

Certainly one would not use a generic piping leak sealant in a refrigeration system because of the risk that it would clog up the expansion valve, capillary tube or other components. But a product specifically designed for refrigeration systems and approved by HVACR manufacturers should have wide application for repairing smaller leaks.

A complaint I have and one that is voiced by some HVACR repair contractors is that refrigerant leaks should be found and repaired properly: if you don't know where the leak is there is a risk that you are leaving a bigger problem un-attended, generating a nasty pond of leak sealant outside the system, and causing an un-necessary and recurrent addition of refrigerant to the system.

Watch out: I would certainly not attempt to repair leaks in a refrigeration system in which the cooling coil or other components are badly corroded and fragile by using an additive-sealant nor by brazing because you are probably throwing good money after bad. Corroded leaky HVACR coils should be replaced.

And I would be alert for broken, cracked, or poorly-brazed refrigerant-tubing that is way too big for these products to work at all, even if you don't mind clogging the TEV.

The bottom line that I think the industry reaches on the "should I use refrigerant leak seal agents" is ... it depends. For a small, remote, hard-to-find refrigerant leak the products may work successfully, while larger leaks need to be found and fixed in more traditional means such as replacing a damaged section of refrigerant tubing or re-brazing a bad joint.


Reader follow-up:

re: A/C issues-blowing warm air said: The service technician used A/C Leak Freeze™.

Reply: Information about A/C Leak Freeze™ and other refrigerant system eak "Stop-Leak" products

That's a valid product intended for refrigeration leak repair and according to the manufacturer, is OEM approved for nearly all refrigerants. "Stop leak" products have been in use for decades, particularly in the automotive industry where they were used to address leaks in automotive cooling systems.

Those products traditionally used a carrier and fibers (originally asbestos) - an approach not suitable for refrigeration systems whose refrigerant metering devices may not tolerate particulates, even small ones.

Since the 1980's several inventors (e.g. Packo & Bailey 1980, 1982, 1984) have patented other approaches (and chemistry) for sealing small leaks in refrigeration systems.

We don't know the active ingredient in A/C Leak Freeze™ but similar products use triethoxyl (vinyl) silane that forms a seal when exposed to air and can seal small openings in refrigeration systems without clogging up the capillary tube or thermostatic expansion valve.

AC Leakfreeze products provided by Universal Technologies Inc are provided in three versions given below. The sealant is intended for injection into the A/C or heat pump system's refrigeration piping system via a service port, usually on the low-side. Injection is accomplished using a syringe type injector provided by the manufacturer.

Installation instructions discuss the appropriate pressure levels in the system, the injection procedure, and sequence of operations. After the sealant is injected into the refrigerant system where it is mixed with refrigerant, the running compressor circulates the refrigerant/sealant mix through the refrigeration piping system with the intention that the sealant will find and seal leaks in the coils or piping system up to 0.5mm in size.

Universal Technologies Inc. provides three refrigeration stop leak products:

  1. AC Leak Freeze™ is a sealant product sold in a 1.5 oz. dose for AC & Refrigeration systems from 1-6 tons in size or in a 2.0 oz dose for system between 6-12 tons in capacity. Larger doses are required for AC or refrigeration systems of larger size. The company says that this product ...

    Will stop leaks of refrigerant gas in appliance and refrigeration systems. AC Leak Freeze™ is compatible with ALL refrigerants and oils except ammonia. Our R22 leak sealer products will permanently seal your air conditioner leak or refrigerator gas leak.
  2. AC Leak Freeze™ with "Magic Frost Dose" includes the sealant product and additives the company reports will improve compressor lubrication and clean the system, extending compressor life and reducing noise. The product is sold in the same dosage sizes as AC Leak Freeze™
  3. AC Leak Freeze™ R Dose - intended for smaller refrigeration appliances using 4-16 oz of refrigerant, and in a dose size of 0.5 oz. The company warns that the sealant cannot exceed 10% of the system refrigerant charge volume.

The following is an excerpt from the manufacturer's product literature:

AC Leak Freeze™ will stop leaks of refrigerant gas in HVACR air conditioning and refrigeration systems in homes and commercial buildings. This HVAC maintenance ensures that any air conditioner leak will be permanently sealed. AC Leak Freeze™ is suspending until it mixes with the refrigerant.

AC Leak Freeze™ is activated by refrigerant escaping at the site of a leak — forming a chemical weld and sealing the leak.

AC Leak Freeze™ is compatible with all standard refrigerant gases. It’s polymer-free, tested to be non-clogging to the A/C compressor and recovery unit — it’s a permanent fix. AC Leak Freeze™ with Magic Frost provides all the benefits of AC Leak Freeze™ plus extends compressor life and reduces noise, improves A/C system lubrication and reduces friction.

It cleans and revitalizes the A/C system while reducing energy consumption. - Universal Technologies Inc., A/C Leak Freeze product information at, retrieved 21 July 2015

The sealant is injected into the low side of the A/C or refrigeration unit by the low side service port. After injecting the sealant, if additional refrigerant is needed it is added at this time. The compressor should be kept running for at least 30 minutes after sealant injection.

A review of the AC Leak Freeze™ MSDS does not disclose any information about the ingredients of this product except that it is a mixture. The product literature notes that the sealant is not a polymer.

Reader follow-up

A/C issues-blowing warm air said:

Last summer, the system wasn't cooling. The repairman added 2 lbs of refrigerant and everything was okay. This summer, again, the system wasn't cooling.

The same repairman came out, added a pound of refrigerant and said I should put in the AC Leak freeze because it shouldn't have lost a pound. I added it but was still having issues.

Called repairman back out. that was when he said it could be the TXV, but he found the a-coil extremely dirty and cleaned it as well as he could without cutting it out and bathing it.

When I say "With the thermostat set to 73 degrees, it's running closer to 80..." I mean with the thermostat set to 73, it registers 80 degrees for the indoor temperature. Sorry for the confusion. The coil as well as the outside line is barely getting cool to the touch.

The system is barely cooling and the outside (condensor) fan runs for about 15 minutes then shuts off. It used to run as long as the inside blower was running.

I'm not sure what else to try but I'm getting tired of paying the service guy $100+ every week with no change. The entire system is only 4 years old.

Reply: more on diagnosing low refrigerant vs a blocked cooling coil


Adding 2 lbs of refrigerant means your system was probably close to empty. That's a pretty big leak. A pound a year is a big refrigerant leak for a residential A/C or heat pump system.

Normally a refrigeration system loses ZERO refrigerant. The charge is permanent unless there is a leak.

A dirty evaporator (cooling) coil will also reduce the cooling out put of a system because it blocks air flow. You may find the cooling coil also ices over because of the reduced air flow across it.

To distinguish between low refrigerant and a dirty coil (or dirty air filter or other duct defect) for the homeowner is relatively simple. If the air flow at your supply registers is weak I suspect one of the latter issues. If the air flow is strong but the air is not cool I suspect low refrigerant or a TEV that's not metering refrigerant properly.

at AIR CONDITIONER TEMPERATURES we give typical A/C system temperatures you should find.

at AIR CONDITIONER TEMPERATURE MEASUREMENT we describe how to measure A/C temperatures for diagnostic purposes.

If your A/C system can't get the indoor temp below 80, unless you've got windows and doors open or some unusual heat gain situation, your A/C system is not working.

Where to Buy AC Refrigerant Leak Sealants

A/C refrigerant system sealant products include both sealants and refrigerant re-charge kits with a leak sealant included.

Watch out: most of these refrigerant leak products include instructions that require that the stop-leak product be added by a trained HVACR technician and some require measurement of the air conditioner, heat pump, or other refrigeration equipment pressure levels as part of the procedure.

Special equipment and education are required to perform those tasks properly and safely, and failure to do so can result in personal injury or expensive damage to the cooling equipment.

How do A/C Refrigeration Leak Sealants Work - Research

Using triethoxyl (vinyl) silane, probably the active ingredient that acts as a sealant in A/C Easy Seal™ as an example, the silane adheres to the metal surfaces around a pinhole leak in the refrigerant tubing to form a seal.Packo (1982 and others) patented this method, and Flis (2006) notes the role of exposure to air in this process. A nice benefit of the coating that is formed is the increased resistance to future corrosion at the leak site.

Watch out: inappropriate or incorrect application of a refrigerant leak sealant product can damage a refrigerant metering device such as a capillary tube or thermostatic expansion valve and might damage the HVACR compressor as well. (Glaeser (1999) discusses compressor failure due to reed valve fracture - an event more likely to occur from overcharging and liquid slugging.)

References & Research About A/C Refrigerant System Leaks & Sealants

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS.

As we explain in our articles on lost cooling capacity or air conditioning systems or heat pumps that are not working, a refrigerant leak in your air conditioner or heat pump means that eventually it will just not produce cool air (during air conditioning) nor warm air (during heating if it's also a heat pump).


Continue reading at DIAGNOSE NEED to REPLACE COOLING COIL or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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