Refrigerant: Description and Operation
Commercial designation
Obtain R-134a refrigerant (tetrafluoroethane) from a local A/C supplier under one of the following names:
- H-FKW 134a
- SUVA(R) 134a
- KLEA 134a
NOTE: R-134a refrigerant is packaged in different containers. Use only R-134a that comes in containers having correct types of service fitting.
Color
Refrigerant R-134a is colorless and is invisible as a gas. Only the layer between gas and fluid is visible (fluid level in tube of cylinder or bubbles in sight glass in fluid reservoir.) R-134a when viewed through a sight glass (if installed) may appear milky due to the mixing of refrigerant and lubricating oil (PAG oil).
Airborne properties
Escaped refrigerant gases are heavier than air and will gather first in low places, like under the car. R-134a refrigerant gas displaces oxygen and may cause suffocation in low areas of poor air circulation.
Solubility of refrigerant oil
A required special refrigerant oil Polyalkylene Glycol (PAG) synthetic oil is used to lubricate cylinder walls and bearings and enters the refrigerant circuit to some degree. This oil is NOT compatible with mineral based oils used in R-12 systems.
NOTE: R12 refrigerant systems use mineral oils which are not dissolved by R-134a refrigerant and are unusable.
Effects on the environment
Because R-134a does not contain chlorine atoms, the major catalyst in ozone depletion, R-134a has no ozone depletion potential.
R-134a does not cause smog and has a considerably lower global warming potential (greenhouse effect) than R-12 refrigerant. Nonetheless, do not release R-134a into the environment and always recover/recycle using approved service equipment.
Toxicity
Refrigerant R-134a is non-toxic up to a temperature of 101 °C (214 °F) and is safe when handled and used properly.
Above 101 °C (214 °F), gas pressure is above 39.5 bar (573 psi) and R-134a begins to decompose into poisonous gases (hydrogen fluoride, carbonyl fluoride and fluorine). These gases give adequate warning of their presence since they cause irritation of the mucous membrane (throat).
Refrigerant R-134a gas has no effect on foodstuffs; it does not poison food or make it inedible.
Temperature/pressure relationship
In a not fully charged refrigerant container, refrigerant gas comes to the surface which under particle formation becomes fluid. This occurs under pressure and is know as gas pressure. Similar to R-12 refrigerant, the gas pressure of R-134a is temperature dependent.
Temperature in °C (°F) Pressure in bar (psi)
-30 (-22) 0.0 (0.0)
-20 (-4) 0.3 (4.4)
-10 (14) 1.0 (14.5)
0 (32) 1.9 (27.5)
10 (50) 3.1 (45.0)
20 (68) 4.7 (68.2)
30 (86) 6.7 (97.2)
40 (104) 9.1 (132.0)
50 (122) 12.2 (177.0)
60 (140) 15.8 (229.2)
70 (158) 20.2 (293.0)
WARNING!
Paint repairs on vehicles with A/C:
- While performing body/paint repairs involving the use of preheating or driving ovens, do not expose any component of A/C system to temperatures above 80 °C/176 °F.
- Excessive heat will cause a pressure increase which could burst the system.
- Temperature/pressure chart See "A/C System (R-134A), Pressure & Temperature Relationships". Pressure, Vacuum and Temperature Specifications
Effects on plastics
Refrigerant R-134a will deteriorate some plastics. When system temperature drops, these plastics can be deposited at the expansion valve or restrictor causing blockage. Therefore, when making system repairs, use only genuine Audi replacement parts which are specified for use with R-134a refrigerant.
Effects on metal
In its pure state, refrigerant R-134a is chemically stable and will not attack iron or aluminum. However, the mixture of R-134a and PAG oil may deteriorate certain metals (copper) which could lead to blockage, leaks or deposits on the compressor piston. Therefore, when making system repairs, use only genuine Audi replacement parts which are specified for use with R-134a refrigerant.
Critical temperature/critical pressure
R-134a refrigerant will remain chemically stable up to a pressure of 39.5 bar (573 psi). This corresponds to a temperature of 110 °C (230 °F). Above this temperature the refrigerant deteriorates (see flammability).
Water solubility
Liquid R-134a refrigerant will absorb only very minute quantities of moisture. However, R-134a vapor can absorb large amounts of moisture.
Water in the system forms ice in the expansion valve or restrictor causing the system to slop cooling. In addition, moisture combines with the refrigerant to form acids which will damage the system.
Flammability
R-134a refrigerant is not flammable. In fact, it tends to inhibit combustion and has a fire extinguishing effect. However, a flame or glowing hot surface, as well as ultraviolet light (from electric welding), will decompose the refrigerant into poisonous gases (hydrogen fluoride, carbonyl fluoride and fluorine). These gases give adequate warning of their presence since they cause irritation of the mucous membrane (throat).
R-134a can become flammable at pressures above ambient pressure in conjunction with air concentrations greater than 60% by volume.
Refrigerant containers
There must be pressure space available in the fluid area of the container. At increasing temperatures the fluid expands, the space filled with vapor becoming smaller. At a specific point there will only be fluid in the container. Beyond this point, only a slight increase in temperature will result in a very high pressure in the container.
Without sufficient room for expansion of R-134a (gas cushion), the container could explode when the temperature rises causing serious injury.
DO NOT exceed maximum rated capacity of refrigerant containers. Never fill a container to more than 60% of its gross weight rating (for example, 18 lb in a 30 lb container.)
Leak detection
Use halogen leak detector Hitec HI400A-TEL, or equivalent, to check for R-134a system leaks. This tool can also be used to detect leaks in R-12 systems. Many currently available R-12 leak detectors cannot detect R-134a refrigerant leaks.