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Air conditioning system with refrigerant R134a - Edition 10.2014
1.6.4
Physical properties of R134a
Because the vapour pressure curves of R134a and other refrig‐
erants are in part very similar, unique identification on the basis
of pressure alone is not possible.
The air conditioner compressor used for R134a is lubricated with
special synthetic refrigerator oils, such as PAG oils (polyalkylene
glycol oils).
1.6.5
Effects on metal
In its pure state, refrigerant R134a is chemically stable and does
not attack iron or aluminium.
However, impurities such as chlorine compounds in the refriger‐
ant do attack certain metals and plastics. This can lead to block‐
ages, leaks and deposits on the air conditioner compressor
piston.
1.6.6
Critical temperature and critical pres‐
sure
Up to a gas pressure of 39.5 bar positive pressure (corresponding
to a temperature of 101°C) the refrigerant R134a remains chem‐
ically stable; however, above this temperature the refrigerant
decomposes (see Combustibility).
1.6.7
Water content
Only very small amounts of water are soluble in liquid refrigerant.
On the other hand, refrigerant vapour and water vapour mix in
any proportion.
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Any water present in the refrigerant circuit will be carried along as
droplets. The dryer, dryer bag or dryer cartridge in the receiver or
reservoir are capable of holding approx. 7 grams of water before
they are full and cannot absorb any more water. If there is further
water in the circuit, it will flow to the expansion valve jet or to the
restrictor and becomes ice.
The air conditioning system will stop cooling.
Water destroys the air conditioner because at high pressures and
temperatures it combines with other impurities to form acids.
1.6.8
Combustibility
Refrigerant is non-flammable. On the contrary, it has a fire-inhib‐
iting or fire-extinguishing effect. Refrigerant decomposes when
exposed to flames or incandescent surfaces. UV light can also
decompose refrigerants (UV is emitted by electric arc welding).
Products of this decomposition are poisonous and must not be
inhaled. However, these chemicals irritate the mucous mem‐
branes, giving adequate warning of their presence.
1.6.9
Charge factor
There must be space both for liquid and vapour in a container. As
the temperature rises, the liquid expands. The space occupied by
the vapour becomes smaller. Eventually, there will only be liquid
in the container. After that time, even a small increase in temper‐
ature will result in a very large increase in pressure, since the
liquid is seeking to expand further but there is no space for it to
do so. The resulting forces are sufficient to burst the container.
To prevent containers from being overcharged, regulations gov‐
erning the storage of compressed gases specify how many kilo‐
grams may be charged into a container for every litre of container
volume. This charge factor multiplied by the internal volume gives
the permissible charge quantity. The charge factor for the refrig‐
erants used in cars is 1.15 kg/l.
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Rep. gr.00 - Technical data
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