Everything You Need to Know About Using O-Rings in Your Vehicle’s A/C System

If you’ve ever been faced with a broken air conditioner in a car, you know how frustrating it can be. It seems to always happen right in the middle of the hottest day of the summer. If you’ve found yourself sitting in a sweltering car with a puddle of sweat, you’ll definitely be eager to figure out what’s gone wrong as soon as possible. If the problem is a weak or warm airflow, you may be dealing with a tiny leak from one of the seals in the system. 

The air conditioner in your car is a fairly complex system. It works by pushing through a phase-changing liquid/gas mixture, called a refrigerant, through a series of mechanisms. These components change the pressure on the refrigerant, therefore changing its temperature and physical state. These physical changes to the mixture allow for a steady flow of air that’s consistently cooled.

Because the system works by pushing highly pressurized refrigerant through a loop, there must be no gaps or holes in the mechanical structure of the system. The smallest leak can be detrimental to the efficiency of the system and can result in changes in temperature, or even a full break down of the cooling system. Using proper seals for the system is key. The most commonly used seal for a car’s air conditioner is an o-ring.

What’s an o-ring?

An o-ring is a type of seal used to seal off any gaps between mating materials. If you’ve ever come across any type of gasket seal, you’ll be familiar with the concept. An o-ring is a type of gasket that looks like an elastomer loop, or as some like to say, like a donut. The o-ring fits into a groove. When pressure is applied, the shape of the cross-section of the o-ring changes and fills in any gaps of air that still exist between the two materials. 

There are quite a few positive aspects of the o-ring. O-ring seals can be used in static or dynamic applications (unlike other types of gaskets). They are also much more resistant to high pressures and temperatures, and for this reason, are celebrated for their durability and malleability.

O-rings come in a huge array of sizes and colors. The size of an o-ring is determined by measuring either its internal or external diameter and by measuring its cross-section. Different cross-section widths work differently depending on the application, so knowing which width is best for your particular situation is key.

O-rings are usually made of some sort of rubber-like material. Some common types are listed below.

  1. FFKM 

This is a type of fluoroelastomer, best used at high temperatures of up to 650 degrees Fahrenheit. This type of material isn’t suitable in conjunction with alkali metals or freons.

2. Buna-N

This material is a nitrile, suitable at temperatures up to 275 degrees Fahrenheit with water, fuels, and silicone oils. This type isn’t suitable for auto fluids.

3. Silicone

This material can withstand temperatures as high at 400 degrees Fahrenheit. It’s often recommended due to its wide temperature range and its ability to withstand ozone, sunlight, and weathering.


EPDM stands for Ethylene Propylene. This material is suitable to interact with substances of up to 300 degrees Fahrenheit. It’s resistant to hot water and steam and auto fluids and is often used in plumbing scenarios. Avoid using this material with petroleum oils or fuels.

There are many other materials available. The best option is to look for an o-ring that’s made with your specific application in mind. In this case, you’ll be looking for an o-ring that works well with a common refrigerant. We recommend HNBR o-rings, which we discuss in further detail below.

Why are they commonly used in air conditioning systems?

O-rings tend to be the seal chosen by most mechanics for air conditioning systems because of their high-performance rate when confronted with extreme temperatures and pressures. The whole system relies on creating very high pressures, and then suddenly reducing these pressures. This environment would be highly volatile for a different type of seal. When installed properly, o-rings can provide a complete and reliable seal.

How to replace an o-ring

First, you’ll need to find the faulty o-ring that’s causing the leak. This can be a challenging undertaking. Refrigerant is designed to be phase-changing, and for this reason, doesn’t leave behind any puddles or pools to indicate where the leak is coming from. First, try to detect any signs of damage or malformation on any of the o-rings in the A/C system.

If you’ve identified a leak in your car’s air conditioning system, it’s very possible that one of the o-rings has been damaged in some way. This can occur naturally over time or can be caused by a chemical reaction with the refrigerant as it passes through. If you notice cracks, bumps, or a change in the o-ring’s natural shape, it’s worth looking into all of the materials and substances that are interacting to ensure that they are compatible. It will be a waste of time to order new o-rings that are bound to break down again due to a lack of research.

If you can’t detect any of the above signs indicating physical damage to the o-ring, you may need to use professional equipment. A professional mechanic can help you use a black light to detect any leaking refrigerant. There’s also a device known as a sniffer that will find the leak if necessary.

To replace the o-ring, you’ll need to pry it out of the groove using a hooked o-ring removal tool. If the o-ring breaks, that isn’t a problem. You’ll then need to slowly work the new o-ring into a perfect position in the groove. Using an o-ring lubricant can be helpful if it’s a very tight fit. Make sure you also look up the ingredients of the lubricant, as some o-rings may have a chemical reaction to these substances.

If you don’t already know the size of the new o-ring required, you can use the old o-ring to determine the correct size (unless, of course, you’re concerned that a poorly fitted o-ring was used). If the old o-ring is still intact, measure the internal or external diameter in millimeters as precisely as you can. You’ll also need a measurement of the cross-section. These two dimensions will tell you the size you require.

If your o-ring has broken in the removal process, finding the diameter measurement is slightly more complicated. You’ll need to measure the longer, external circumference of the loop in millimeters. The simple equation of circumference divided by 3.142 will give you an accurate measurement for the external diameter.  

Where to get the best new o-rings

If you’re looking for new o-rings for your car, there are plenty of options on the market. Aclube.com is a website that offers a vast array of sizes and colors, specifically designed to be used in your car’s air conditioning system. Their HNBR rings seals are made of hydrogenated nitrile. This material is a synthetic polymer that’s produced by saturating the double bonds in nitrile with hydrogen. This process means there are a minimum number of double bonds in the NBR polymers.

These o-rings are essentially super resistant. They will withstand extreme heat, ozone, and chemical corrosion. Superior to regular Nitrile o-rings, HNBR o-rings will work with just about any system and refrigerant.

At Aclube.com, you’ll be able to purchase these high-quality o-rings cheaply and in a pack of ten. You’ll also find a very comprehensive size guide for each o-ring, so you’ll be sure to buy ones of the perfect fit.


We hope this guide has taught you a little more about why o-rings are such a useful tool in the sealing of the auto air conditioning system. Their design will ensure that the refrigerant running through the system stays where it belongs. The relatively high pressure of the refrigerant requires strong and durable seals, which is why o-rings are the perfect sealing option for this application. The high temperatures involved will also be no issue for an o-ring. For HNBR o-rings that are custom made for auto air conditioning units, remember to visit Aclube.com, where you’ll find a great selection of sizes.  

Replacing a faulty o-ring can be a finicky task. After all, they are quite tiny. It’s important that the installation of the new o-ring is done correctly, as any errors can result in more problems. If you think it’s a task best left to a professional, contact your local mechanic. Feel free to enquire about the material and make of the o-rings they’ve chosen!

Once your new o-ring is installed, your car’s air conditioning system will, hopefully, be back to normal. Enjoy the steady, strong blast of cool air, and say goodbye to the days of stifling, airless car journeys this summer.

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