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

13/2/2005

 

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 

General information for A/C system

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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

13/2/2005

 

). 

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 

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