Volkswagen Golf 1999 Service Manual page 3977

General information for A/C system
temperature 00-1, Vapor pressure table for refrigerant
R134a .
Physical characteristics of R134a
The vapor pressure curves of R134a and other refrigerants
are sometimes very similar, therefore it is not possible to
make a certain distinction solely by pressure.
When using R134a, the compressor is lubricated by means
of special synthetic refrigerant oils, e.g. PAG oils
(polyalkylene glycol oils).
Reaction with metals
In its pure state, refrigerant R134a is chemically stable and
does not corrode iron or aluminum.
Refrigerant impurities such as chlorine compounds
however cause corrosion of certain metals and plastics.
This can lead to blockage, leaks or deposits on the A/C
compressor piston.
Critical temperature/critical pressure
The refrigerant R134a remains chemically stable up to a
gas pressure of 39.5 bar (corresponding to a temperature
of 101 C). Above this temperature, the refrigerant
decomposes (refer to "Combustibility").
Water content
Only very small amounts of water are soluble in liquid
refrigerant. On the other hand, refrigerant vapor and water
vapor mix in any ratio.
Any water in the refrigerant circuit will be entrained in
droplet form. Once the dryer, desiccant bag or dryer
cartridge in the receiver or reservoir has absorbed as little
as approx. 7 g of water, then it is saturated and cannot
absorb any more water. If there is still water in the
refrigerant circuit, it flows as far as the nozzle of the
expansion valve or restrictor and turns to ice.
The A/C system no longer has a cooling effect.
Water destroys the air conditioner as it combines with other
impurities at high pressures and temperatures to form
acids.
Combustibility
Refrigerant is non-flammable. In fact, it has a fire-retardant
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13/2/2005