Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

eplacement condensers and evaporators may not deliver the same cooling performance,
and create a problem your customer didn’t have before.
Location of Orifice Tube. [Chris Herbst] Later cars have the orifice tube installed in the
expansion pipe. The joint at which to access the expansion valve is located along the right side
frame rail in the engine compartment. It is where the high side pipe gets a little bit bigger in
diameter. You'll find the OT in that joint. The earlier cars (with very small diameter pipes at the
firewall) had it in the evaporator. The expansion tube location started in 1991, I believe, but that
is not a guaranteed model year for the change. As a 1993 model, your car is sure to have the
OT in the expansion tube.
R134 versus Refrigerant Alternatives. [Editor] The R134 conversion debate seems to be over
and it is widely accepted as an alternative to R12. Numerous other refrigerants are also
approved by the EPA as having met safety and environmental criteria. Unfortunately, the EPA
does not test these alternative refrigerants for compatibility with refrigerant oils, elastomers, and
other components in your car's cooling system. Santech Industries, a major producer of air
conditioning components, has done some tests and found R134 the only acceptable substitution
product for most applications. See the link for more information in the "testing and reference"
section: http://www.santech.com/
Volvo uses HNBR in its black and yellow o-rings (some earlier seals were blue neoprene). They
also recommend the use of ester oil as the replacement lubricant in R12 to R134 conversions.
After testing HNBR and ester oil, Santech rated the following fluids for compatibility with HNBR
seals:
"Poor" compatibility: Freeze 12 (80% R134a and 20% R142b)
"Marginal" compatibility: FR-12 (Frig c: 59% R134a, 39% R124, 2% butane), RB-276
(Freezone:79% R134, 19% R142, 2% mineral oil)
Similar results came from the use of mineral oil instead of ester oil. "Poor" means seal swelling
in excess of 40%; "marginal" between 16 and 40%. They note: "HNBR and Nitrile are used
predominately in air conditioning systems worldwide and were not generally compatible with the
alternate refrigerants." Some of the problems reported from material incompatibility include:
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Seals swelling where they would no longer fit into the glands
Seals splitting open
Seals extruding between metal gland surfaces
Seals turning into a gum type material