Audi A4 Owners & Service Manuals

Audi A4: Refrigerant R134a Characteristics

Commercial Names and Designations

Refrigerant R134a is currently available under the following trade names:

  • H-FKW 134a
  • SUVA 134a
  • KLEA 134a


  • Different trade names may be used in other countries.
  • Of the wide range of refrigerants available, this is the only one which may be used for vehicles. The designations Frigen and Freon are trade names. They also apply to refrigerants which may not be used in automotive vehicles.


Like water, refrigerants are colorless in both vapor and liquid form. Gas is invisible. Only the boundary layer between gas and liquid is visible. (Liquid level in tube of charging cylinder or bubbles in sight glass). Refrigerant R134a fluid may appear colored (milky) in a sight glass. This cloudiness is caused by partially dissolved refrigerant oil and does not indicate a malfunction.

Vapor Pressure

In a partially filled, closed container, the quantity of refrigerant evaporating from the surface equals the quantity returning to the liquid state as vapor particles condense. This state of equilibrium occurs under the influence of pressure and is often called vapor pressure. The vapor pressure is dependent on the temperature. Refer to → Chapter "Refrigerant R134a Vapor Pressure Table"vapor pressure table".

R134a Physical Characteristics

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.

With R134a, the A/C compressor is lubricated with special synthetic refrigerant oils, for example, PAG oils (polyalkylene glycol oils).

Affect on Metal

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/Pressure

General Information

The refrigerant R134a remains chemically stable up to a gas pressure of 39.5 bar (573 psi) (absolute pressure of 40.56 bar (588 psi), which corresponds to a temperature of 101 ºC (214 ºF) ). Above this temperature, the refrigerant decomposes. Refer to → Chapter "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 in the receiver or reservoir has absorbed as little as approximately 7g of water. This water 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.


Refrigerant is non-flammable. It actually has a fire-resistant or fire 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 container must have space for vapor as well as liquid. As the temperature rises, the liquid expands. The space filled with vapor decreases. At a certain point, there will only be liquid in the container. Beyond this, even a slight increase in temperature causes high pressure to build up in the container as the liquid tries to continue expanding even though there is not enough space for it. The forces that result are strong enough to rupture the container. To prevent a container from being overfilled, the regulations regarding compresses gasses specify how many kilograms of refrigerant that may be added to a container per liter of interior volume. The product of multiplying this charge factor by the internal volume of the container is the permissible capacity. The figure for refrigerant used in vehicles is 1.15 kg/liter.

Evidence of Leaks

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, by using an electronic leak detector or by introducing a UV-leak detection additive into the refrigerant circuit. Electronic leak detectors are capable of registering leaks with refrigerant losses of less than 5g per year.


Use leak detectors designed for the type of refrigerant. For example, a leak detector for R12 refrigerant will not work with R134a because R134a refrigerant has no chlorine atoms so the leak detector will not respond to it.


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