But
the straight truth about o-rings is that In recent years, they have become
available in an assortment of different colors. It would be very convenient
if the color represented the material, but it does not. Therefore, just because
the factory o-ring is green and the replacement one is green does not necessarily
mean that they are both of the same rubber compound nor that the replacement
one is acceptable for use in your system.
Likewise,
when servicing an auto A/C system, you may find that the original factory
o-rings are purple, yellow or tan or one of several other different colors,
and the replacement you have is green. It’s important to understand
that the color of the o-ring does not matter. What does matter is if the
replacement o-ring being installed is manufactured from the proper compound.
All
the issues about colored o-rings became compounded when auto A/C systems
had to be retrofitted (for use with R-134a refrigerant). Part of the recommended
retrofit procedure was to change o-rings. That was because rubber compounds
used for R-12 and mineral oil would not withstand the chemical mixture of
R-134a and Ester or PAG oil, nor would they withstand the higher heat from
higher operating pressures.
As
we already stated, the color of the o-ring in no way implies (or confirms)
what material the o-ring is made of. The only important issue (besides the
right size) is that the o-rings you use are manufactured from the right material.
Having said that, you would think it’s pretty simple, right? If all
suppliers used the same o-ring material, then all o-rings would be compatible.
We’re
sorry to advise you that this has never been the case. The issues of o-ring
colors was further complicated during the rush to retrofit. The concept of
‘blue’ o-rings was introduced (although it’s never been determined
why). What really happened was that, at the start of the major retrofit period,
the original equipment manufacturers changed most of the o-ring seals on
new vehicles to ‘green’. This became a (not official) standard
as manufacturers changed most o-ring compounds to HNBR (Hydrogenated Nitrile
Butadiene Rubber) for better resistance to heat. However, being as creative
as some suppliers can be, they simply used older black o-rings that were
actually ‘painted’ blue, just to try and confuse you. (It must
have been to confuse you because there is absolutely no reason to paint an
o-ring. None whatsoever!). In fact, if you find you have any of these
‘painted’ o-rings, they should be discarded. The peeling paint
can only contaminate your A/C system.
Also
understand that part of the problem with various colors of o-rings occurrs
because vehicle manufacturers typically outsource complete A/C assemblies
(or systems). The component manufacturer’s supplying the vehicle manufacture
may use one color o-ring while the vehicle manufacturer assembles the rest
of the system with another color o-ring. Therefore, complete service kits
for some vehicles include a variety of different o-ring colors. However,
keep in mind that the color really doesn’t matter. It’s the material
used that counts.
So
what o-ring material is acceptable? In order to provide the absolute best
answer, each specific application would have to be tested. By that, we mean
that each refrigerant and oil mix should be tested throughout the various
heat ranges. However, we know that specific testing is not practical, therefore
we will show you the guidelines you should follow when selecting replacement
o-ring seals.
There
are three generally acceptable o-ring materials for automotive A/C systems.
They are Nitrile, HNBR (Hydrogenated Nitrile Butadiene Rubber) and Neoprene.
Extensive testing has proven the HNBR provide the best seal across all R-134a
refrigerant and oil mixes throughout all the temperature ranges. Typically,
HNBR o-rings are referred to as the ‘high temperature’ o-ring for
R-134a sysetms. Over time, they shrink and/or expand the least. In some
applications, you may find Nitrile or Neoprene used on the low side of the
system only, where components are not subject to higher operating pressures
and temperatures.
Therefore,
understanding that the color of the o-ring really doesn’t matter, you
should always use HNBR o-rings for replacements. They can be used on both
the high and low side of the system without fear of excessive shrinkage or
swelling.
How
can you tell what the o-ring material is? Without specific testing
of each o-ring for the material, you really can not tell. You should make
it a point to purchase o-rings from reputable suppliers and they (almost
always) advise of the o-ring material. Keep in mind that o-rings are one
of the lowest priced components of the A/C system, but it’s so important
to use the right ones.
O-Ring
Compatibility :
So that you best understand the major differences in o-ring materials and
their compatibility, we have provided a table (below) that shows the various
o-ring materials (Nitrile, HNBR and Neoprene) and their compatibility with
various refrigerants and oils. Keep in mind that this chart makes no
consideration for heat ranges. Tests have proven that HNBR is the best across
all heat ranges; Nitrile is acceptable for lower (or mid) heat ranges. Neoprene
is only acceptable for low temperature ranges. This chart in no way represents
a warranty or guarantee of compatibility as only specific testing can provide
absolute assurance. The chart should be used as a guideline. |
This
was probably one of the best books on recharging air conditioning that I
have seen...
