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Topic
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O-Ring Color Changes
Prior to 1987, O-Rings for R-12 mobile AC applications were almost exclusively black.
Material-wise, the rubber in these O-Rings may have been Nitrile (Buna-N), Neoprene, or a blend
of these two compounds. In 1987, the Montreal Protocol mandated the change to a non-ozone depleting
refrigerant and OEMs around the world unanimously selected R-134a as the refrigerant
to replace R-12. In the aftermarket, refrigerants were offered that were blends of various base
refrigerants. Whether using R-134a or a blend of other refrigerants, the common trait among these
new refrigerants is that a different O-Ring compound was recommended for sealing. Several
new rubber compounds were identified as being suitable for sealing R-134a and the blend
refrigerant. The O-Rings that were made from these new rubbers have commonly been colored in
order to distinguish them from the earlier black O-Rings that were compatible only with R-12.
Over the past 15 years, O-Rings used in sealing hoses and components of mobile AC systems
have routinely been one of three colors: black, blue, or green. Black O-Rings offered by Four
Seasons are Neoprene and are fully compatible with R-134a, however, it is impossible to look at a
black O-Ring and tell if it is Nitrile (R-12) or Neoprene (R-134a). That is the reason colors have
been adopted. Blue and green have become the standard colors for those applications. The blue
O-Rings that are available today are Neoprene. They are colored blue with an external coating to
distinguish them from black nitrile O-Rings that are identical in appearance yet not recommended
for use with R-134a. The green O-Rings are Highly Saturated Nitrile (also known as
Hydrogenated Nitrile) and are commonly referred to as HNBR or, in some cases, HSN. In either
case, the green color is molded into the rubber. The blue Neoprene and green HNBR O-Rings are
interchangeable in their applications with R-134a, blended refrigerants, and R-12 as well.
Recently, there has been a move to consolidate the black Neoprene, blue Neoprene, and green
HNBR O-Rings offered in the Four Seasons product line to all green HNBR O-Rings. The
rationale behind this is that if all these O-Rings are equally compatible with R-134a, then it is
unnecessary to offer more than just one type. The elimination of the numerous duplicate part
numbers for black, blue, and green O-Rings will offer obvious benefit and will result in a general
simplification of the O-Ring selection process. The elimination of black Neoprene from the mix
is obvious as this compound presents an identification problem for the service technician. The
reason for selecting green HNBR over blue Neoprene is twofold. First is the fact that green
HNBR has OE acceptance and application whereas blue Neoprene has been predominantly an
aftermarket phenomenon. The second reason is because green HNBR has a slightly higher
operating temperature range when compared to Neoprene which makes it the slightly more
desirable choice. Add to these the earlier mentioned benefit of a large reduction in O-Ring SKUs
through the elimination of black and blue O-Ring part numbers and you have a clear picture of
why this change taking place.
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Replies
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interesting. i think they should keep the different colors for easier identification. also would the green o rings be gasohol resistant?
I don’t think they are designed for that. They are designed to prevent refrigerant leaks not fuel leaks.
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