O-rings are common seals used in many industrial applications.  There is a wide range of materials from which O-rings can be made, and that material affects the way a particular O-ring will function.  Some materials are more durable, others more elastic.  Some can withstand high temperatures and others are more tear-resistant.

Because of their low cost, ease of production and installation, flexibility  and resistance to pressure, O-rings have found their way into air conditioning systems .  OEMs know to choose the proper O-rings when they assemble a system, and it is important when replacing them that the proper choice is made again.

Standard O-rings are NBR (also called Nitrile Rubber, Buna-N, or just Buna).  NBR O-rings usually shrink a little and may cause leakage problems. These O-rings are suitable as general purpose seals as they are resistant to tears and abrasion.  They work well in applications which have limited temperature and resistant requirements (not A/C!).

Many O-rings used in marine and industrial systems are made of Viton, which is a fluorocarbon rubber that excels in sealing applications which involve movement. Viton O-rings sometimes are brown, or black with a blue stripe, or just black.   Although they are  used in many automotive applications, Viton O-rings are NOT compatible with refrigerants. You won’t find them in any OEM AC  system and you should never use it for replacements.  Neoprene O-rings can seal refrigerants in refrigeration and A/C systems, however, since they are compounded with lead they should not be handled frequently as they are hazardous to human health.

A better type of O-ring for air conditioning applications is HNBR which stands for Hydrogenated NBR (sometimes called Hydrogenated Nitrile, or Highly Saturated Nitrile Rubber, or HNB). The compatibility of HNBR with Mineral oil, PAG, POE, R-12, R-134a, R-1234yf is very good.  Another advantage is that its temperature range is -22F to 302F.  HNBR are frequently green, but they can be black also, or other colors.

When you look at FJC O-rings and O-ring kits you’ll always notice the statement “All O-rings are High Temperature HNBR”.  This statement underscores our commitment to our end users that every O-ring FJC sells is suitable for automotive air conditioning systems and exposure to refrigerants and lubricants.

LMK 2019


HNBR O-rings
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