Volkswagen Golf / Golf GTI / Jetta. Manual — part 995

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

General information for A/C system

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or extinguishing effect. Refrigerant decomposes when
exposed to flames or red-hot surfaces. UV light (occurring
for example during electric welding) also causes refrigerant
decomposition. The resultant decomposition products are
toxic and are not to be inhaled. However, irritation of the
mucous membranes provides an adequate and timely
warning.

Charge factor

A vessel must have space for vapor as well as liquid. As
the temperature rises, the liquid expands. The vapor-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 avoid overfilling of
vessels, regulations governing compressed gases specify
the number of kilograms of refrigerant with which a vessel
may be filled per liter of internal vessel volume. The
product of multiplying this "charge factor" by the internal
volume of the vessel is the permissible capacity. The figure
for refrigerant used in vehicles is 1.15 kg/liter.

Leak detection

External damage, for example, can cause a leak in the
refrigerant circuit. The small quantity of refrigerant escaping
from minor leaks can be detected for example using an
electronic leak detector or by introducing a leak detection
additive into the refrigerant circuit. Electronic leak detectors
are capable of registering leaks with refrigerant losses of
less than 5 g per year. (Use must be made of leak
detectors designed for the composition of the respective
refrigerant. For example, a leak detector for R12 refrigerant
is not appropriate for R134a, as R134a refrigerant has no
chlorine atoms and the leak detector does not therefore
respond).

Refrigerant oil

Refrigerant oil mixes with the refrigerant (about 20-40%,
depending on compressor type and amount of refrigerant)
and circulates constantly in the system, lubricating the
moving parts.

Special synthetic refrigerant oils, e.g. polyalkylene glycol
(PAG) oil, are used in conjunction with R134a air
conditioning systems. This is necessary as mineral oil, for
example, does not mix with R134a. In addition, the
materials of the R134a air conditioning system could be
corroded as a result of mixture flowing through the

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refrigerant circuit under pressure at high temperatures or
breakdown of the lubricating film in the compressor. The
use of non-approved oils can lead to the failure of the air
conditioning system and exclusive use is therefore to be
made of authorized oils.

Parts Catalog

Type of oil for R134a in motor vehicles: PAG

Note:

- Do not store refrigerant oils in open containers as they are
extremely hygroscopic (water-absorbing).

- Always keep oil containers sealed.

- Do not re-use old refrigerant oil. Dispose of as used oil of
unknown origin (refer to Disposal/Environmental Protection,
Vol. 2-2. 43.1).

- Ester-based oils are only intended for use with large
systems (not for motor vehicle air conditioners).

Characteristics of refrigerant oil

The most important properties are a high degree of
solubility with refrigerant, good lubricity, absence of acid
and minimal water content. It is therefore only permissible
to use certain specified oils. For list of approved refrigerant
oils and capacities, refer to

.

Repair Manual, Heating & Air Conditioning, Repair

Group 87 ,

PAG oils, which are appropriate for refrigerant R134a, are
highly hygroscopic and do not mix with other oils. Opened
containers should therefore be closed again immediately to
prevent ingress of moisture. Moisture and acids promote
ageing of refrigerant oil, causing it to become dark and
viscous as well as corrosive towards metals.

Note:

- For refrigerant circuits with refrigerant R134a, only the oil
approved for the A/C compressor may be used. (Capacities

Repair Manual, Heating & Air Conditioning, Repair

General information for A/C system

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).

Group 87 ,

- On account of its chemical properties, refrigerant oil is not
to be disposed of together with engine or gear oil

Disposal/Environmental Protection, Vol. 2-2. 43.1 .

Comfort

A basic requirement for concentration and safe driving is a
feeling of comfort in the passenger compartment.
Especially when it is hot and humid, comfort can only be
attained through the use of air conditioning. Comfort can of
course also be enhanced by opening windows/sun roof or
increasing the air output, such a course of action is
however associated with certain drawbacks for the
occupants of the vehicle, e.g. more noise, draughts,
exhaust fumes and unfiltered pollen (unpleasant for allergy
sufferers).

Climate control together with a good heating and ventilation
system concept can create a sense of wellbeing and
comfort by regulating temperature, humidity and air
circulation in the passenger compartment to suit ambient
conditions, with the vehicle both stationary and moving.

Other important advantages of air conditioning:

- Purification of the air supplied to the passenger
compartment (dust and pollen, for example, are washed
out by the moist fins of the evaporator and removed with
the condensate).

- Pleasant temperature levels (example: Mid-size car after
short travelling time, ambient temperature 30 C in the
shade and vehicle exposed to sunlight).

With A/C system

Without A/C system

Head area

23 C

42 C

Upper body area

24 C

40 C

Foot area

30 C

35 C

Environmental aspects

Since roughly 1992, the air conditioning systems of newly
manufactured cars have been successively converted to
refrigerant R134a. This refrigerant contains no chlorine and
therefore does not deplete the ozone layer.

Until roughly 1992, refrigerant R12 was used for air
conditioning systems. Due to its chlorine atoms, this CFC
has a high potential for depleting the ozone layer as well as

General information for A/C system

13/2/2005