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Air conditioner with refrigerant R134a - Edition 11.2018
2.7.5
Reaction with metals
In its pure state, refrigerant R134a is chemically stable and does
not corrode iron or aluminium.
However, refrigerant impurities such as chlorine compounds
cause corrosion of certain metals and plastics. This can cause
blockages, leaks and deposits on the air conditioner compressor
piston.
2.7.6
Critical temperature/critical pressure
The refrigerant R134a remains chemically stable up to a gas
pressure of 39.5 bar (40.56 bar absolute pressure; corresponds
to a temperature of 101 °C). Above this temperature, the refrig‐
erant decomposes (see "Combustibility").
2.7.7
Water content
Only very small amounts of water are soluble in liquid refrigerant.
In contrast, refrigerant vapour and water vapour mix in any ratio.
Any water in the refrigerant circuit will be entrained in droplet form
once the dryer in the receiver or reservoir has absorbed approx.
7 g of water. This water flows as far as the expansion valve nozzle
or the restrictor and turns to ice. The air conditioner will then no
longer provide any cooling effect.
Water causes irreparable damage to the air conditioner because
at high pressures and temperatures it combines with other im‐
purities to form acids.
2.7.8
Combustibility
Refrigerant is non-flammable. In fact it has a fire-inhibiting or fire-
extinguishing effect. Refrigerant decomposes when exposed to
flames or red-hot surfaces. UV light (produced for example during
electric welding) also causes refrigerant decomposition. The re‐
sultant decomposition products are toxic and must not be inhaled.
However, these chemicals irritate the mucous membranes, giving
adequate warning of their presence.
2.7.9
Charge factor
A container must have space for vapour as well as liquid. As the
temperature rises, the liquid expands. The vapour-filled space
becomes smaller. At a certain point, there will only be liquid in the
vessel. Beyond this, even a slight increase in temperature causes
great pressure to build up in the vessel as the liquid attempts to
continue expanding despite the absence of the necessary space.
The resultant forces are sufficient to rupture the vessel. To stop
containers being overfilled, regulations governing the storage of
compressed gases specify the number of kilograms of refrigerant
with which a container may be filled per litre of internal volume.
The maximum permissible capacity is calculated by multiplying
this "charge factor" by the internal volume of the vessel. The
charge factor for refrigerant used in motor vehicles is 1.15 kg/litre.
2.7.10
Tracing leaks
External damage, for example, can cause a leak in the refrigerant
circuit. Minor leaks where only a small amount of refrigerant is
escaping can be detected using, for example, an electronic leak
detector or by adding a UV leak detection additive to the refrig‐
erant circuit. Electronic leak detectors are capable of registering
leaks with refrigerant losses of less than 5 g per year.
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Rep. gr.87 - Air conditioning system
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