Volkswagen Tiguan Service and Repair Manual: Refrigerant R134a

Refrigerant R134a Physical Data

Vehicle air conditioning systems make use of the vaporization and condensation process. In this case, one works with a substance which boils easily, designated as refrigerant.

The refrigerant employed is tetrafluoroethane R134a, which boils at -26.5 ºC (-15.7 ºF) at a vapor pressure of 1 bar (14.5 psi).

Chemical formula	CH2F-CF3 or CF3-CH2F
Chemical designation	Tetrafluoroethane
Boiling point at 1 bar (14.5 psi)	-26.5 ºC (-15.7 ºF)
Solidification point	-101.6 ºC (-150.88 ºF)
Critical temperature	100.6 ºC (213 ºF)
Critical pressure	40.56 bar absolute (588 psi) equals 39.5 bar pressure (573 psi)

Critical Point

Vehicle air conditioning systems make use of the vaporization and condensation process. In this case, one works with a substance which boils easily, designated as refrigerant.

The refrigerant employed is tetrafluoroethane R134a, which boils at -26.5 ºC (-15.7 ºF) at a vapor pressure of 1 bar (14.5 psi).

The critical point (critical temperature and critical pressure) is that above which there is no longer a boundary between liquid and gas.

A substance above its critical point is always in the gaseous state.

At temperatures below the critical point, all types of refrigerant in pressure vessels exhibit both a liquid and a gas phase, i.e. there is a layer of gas above the liquid.

As long as there is still gas present in the container next to the fluid, pressure is dependent on ambient temperature.

Note

Different types of refrigerant are never to be mixed. Only the refrigerant designated for the corresponding A/C system may be used.

Refrigerant R134a Environmental Information

Vehicle air conditioning systems make use of the vaporization and condensation process. In this case, one works with a substance which boils easily, designated as refrigerant.

The refrigerant employed is tetrafluoroethane R134a, which boils at -26.5 ºC (-15.7 ºF) at a vapor pressure of 1 bar (14.5 psi).

• R134a is a fluorocarbon and contains no chlorine.
• R134a has a shorter atmospheric life span than refrigerant R12.
• R134a does not damage the ozone layer. The ozone depletion potential is zero.
• The greenhouse potential of R134a (Global Warming Potential = GWP) is approximately 1430 (the GWP of carbon dioxide is 1).
• The global warming effect of R134a is ten times less than that of refrigerant R12.

Refrigerant R134a Characteristics

Commercial Names and Designations

Refrigerant R134a is currently available under the following trade names:

• H-FKW 134a
• SUVA 134a
• KLEA 134a

Note

• 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.

Color

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 vessel, 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. Vapor pressure is dependent on temperature.

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

The refrigerant R134a remains chemically stable up to a gas pressure of 39.5 bar (572.9 psi) (corresponding to a temperature of 101 ºC (213 ºF). Above this temperature, the refrigerant decomposes.

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.

Only a small drop of water may get into the refrigerant circuit. The dryer, dryer bag or dryer cartridge contained in the reservoir can absorb approximately 7 grams of water. They are then saturated and cannot absorb any more water. If water is still present in the refrigerant circuit, it flows up to the expansion valve nozzle or restrictor and becomes ice.

The air conditioning system stops cooling.

Water destroys the air conditioner as it combines with other impurities at high pressures and temperatures to form acids.

Combustibility

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 vessel 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 vessel. Beyond this, even a slight increase in temperature causes high pressure to build up in the vessel 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 vessel. To prevent a vessel from being overfilled, the regulations regarding compressed gasses specify how many kilograms of refrigerant that may be added to a vessel per liter of interior 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.

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 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 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.

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, for example, 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 refrigerant circuit under pressure at high temperatures or breakdown of the lubricating film in the compressor. Using non-approved oils can cause the HVAC system to malfunction. Only use approved oils.

Refer to the Parts Catalog.

Type of oil for R134a in motor vehicles: PAG

Note

• Do not store open containers of refrigerant oil because it attracts moisture.
• Always keep oil containers sealed.
• Do not use old refrigerant oil over again.
• Used oil disposal: Volkswagen InfoNet; Operations; Handbooks & Dealer Literature; Service Handbook; 15. Environment Protection. Follow the link "Environment Protection in Market- and Service Operations" under general information; 4. Waste Management; 6. Methods of Disposals; g. Disposing of Used Refrigerant Oil
• Used refrigerant oils from systems employing halogenated hydrocarbons (at least one hydrogen atom is replaced, for example, with the halogen elements fluorine, chlorine, bromine or iodine) are to be disposed of as waste subject to special supervision. They are not to be mixed with other oils or substances. Proper storage and disposal must be ensured in line with local regulations. Refer to the chemical-climate protection provision and the recycling and disposal regulations in Germany. Different specifications and rules may apply in other countries.
• German technical, work safety and accident prevention regulations can be obtained from
• Addresses in other countries can be obtained from the relevant authorities.
• Ester-based oils are only intended for use in large systems, not in passenger vehicle A/C systems.

Refrigerant Oil Characteristics

The most important properties are a high degree of solubility with refrigerant, good lubricity, absence of acid and minimal water content. For these reasons, only certain oils are used. A list of approved refrigerant oils and capacities can be found in the vehicle-specific repair manual.

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 aging of refrigerant oil, causing it to become dark and viscous as well as corrosive towards metals.

Note

• Only use oils approved for the A/C compressor in refrigerant circuits with refrigerant R134a. Refer to the vehicle-specific repair manual.
• Used oil disposal: Volkswagen InfoNet; Operations; Handbooks & Dealer Literature; Service Handbook; 15. Environment Protection. Follow the link "Environment Protection in Market- and Service Operations" under general information; 4. Waste Management; 6. Methods of Disposals; g. Disposing of Used Refrigerant Oil

Comfort

Being comfortable while driving leads to better concentration and safe driving. Air conditioning makes drivers and passengers more comfortable when temperatures or humidity are high. While opening the windows or sunroof or increasing the air flow can make vehicle occupants more comfortable, it also exposes them to more noise, draughts, exhaust, pollen and dust.

A well-designed heating and air conditioning system can increase comfort by controlling the temperature, humidity and air flow inside the vehicle. This is done both when the vehicle is moving and when it is stationary.

Air conditioning also offers these advantages:

• It cleans the air that enters the vehicle interior. The damp fins on the evaporator collect dust and pollen, which is then removed by condensation.
• Temperatures in a mid-size vehicle (for example: after a short drive, outside temperature 30 ºC (86 ºF) in the shade and the vehicle exposed to sunlight).

Area	Temperature with A/C System in Celsius (Fahrenheit)	Temperature without A/C System in Celsius (Fahrenheit)
Head area	23 ºC (73 ºF)	42 ºC (107 ºF)
Upper body area	24 ºC (75 ºF)	40 ºC (104 ºF)
Foot area	30 ºC (86 ºF)	35 ºC (95 ºF)

Environmental Information

Vehicles manufactured after 1992 have air conditioning systems that use refrigerant R134a. This refrigerant does not contain chlorine and does not deplete the ozone layer.

Refrigerant R12 was used through 1992. Due to its chlorine atoms, this CFC has a high potential for depleting the ozone layer as well as a tendency to increase the greenhouse effect.

Conversions are offered for existing systems filled with the ozone-depleting substance R12.

Refer to Repair Manual for A/C systems with refrigerant R12. This repair manual is only available in hard copy.

For environmental protection reasons, refrigerants must not be released into the atmosphere. For laws and regulations.