Design And Function: Refrigerant

In order to remove heat from the passenger compartment a medium that has a lower evaporating temperature than air is used, because heat will always move from a hotter body to a cooler body. The medium that is used is refrigerant R-134a or R-1234yf.

R-134a and R-1234yf are gaseous fluorocarbons. They are chlorine-free and do not harm the ozone layer. However, the refrigerants are still environmentally hazardous as they contribute to the greenhouse effect. It is therefore important that all service work is performed by trained personnel.

R-134a and R-1234yf retain their gaseous form at normal atmospheric pressure, and only condense if cooled down to below -26°C.

R1234yf is used in markets covered by legislation regarding the reduction of greenhouse gases in mobile A/C coolant systems. In other markets, refrigerant R134a is used.

Common properties for all refrigerants 

• can only be mixed with synthetic PAG oils (Polyalkylene glycol) and not with mineral oils
• does not affect metals
• affects some types of plastic, so only special gaskets that are intended for refrigerants should be used
• is not explosive
• is odorless
• is not toxic in low doses
• effectively absorbs moisture
• is heavier than air in gaseous form.

R134a 

Courtesy of VOLVO CARS CORPORATION

R134a is a gaseous fluorocarbon. It is chlorine free and does not damage the ozone layer. However, R134a is still environmentally hazardous as it contributes to the greenhouse effect. It is therefore important that all service work is performed by trained personnel.

R134a retains its gaseous form at normal atmospheric pressure, and only condenses if it is cooled down to below -26 °C.

GWP value (Global Warming Potential) for R134a is approx. 1430, which means that it has a 1430 times greater effect as a greenhouse gas than carbon dioxide, which has a GWP = 1. It is therefore important that all service work is carried out by trained personnel.

R1234yf 

Courtesy of VOLVO CARS CORPORATION

R-1234yf will be used in the European market. In other markets, R-134a will be used. The XC90 is Volvo's first model that uses R-1234yf refrigerant.

The European directive 2006/40/EC stipulates that R-1234yf shall be used in Europe for vehicles developed on new vehicle platforms after 2011. The reason is that R-1234yf is a more environmentally-friendly coolant and has GWP=4.

R1234yf is classified as mildly flammable. It is therefore important that all servicing is carried out by trained personnel and with equipment specifically designed for R1234yf. R1234yf retains its gaseous state at normal atmospheric pressure and only condenses if it is cooled to below approx. -30 °C.

Properties 

R-1234yf gives a reduced A/C effect compared to R-134a due to its thermodynamic properties.

R-1234yf is currently several times more expensive to buy than R-134a.

By allowing the refrigerant to circulate in a closed system and changing its pressure and volume, you can change its temperature to make it boil (vaporize). At the working pressure prevailing in the system's low-pressure side, approx. 170-320 kPa (1.7-3.2 bar), the refrigerant boils at approx. 0-10 °C.

A prerequisite in order for the refrigerant to boil is that heat is available. The heat is taken from the air around the evaporator in which the boiling occurs. When the heat is taken up by the refrigerant the surrounding air becomes colder. It is this cold air that is blown out into the passenger compartment by the climate unit's fan. The heat taken up by the refrigerant in the evaporator is transported to the engine compartment where it is discharged to air from the condenser. The condenser is cooled by the headwind and the engine cooling fan.

Filling amount, refrigerant 

The A/C decal in the engine compartment specifies the correct amount of refrigerant. Different filling amounts apply depending on car model, which refrigerant is used, and whether the car has additional evaporators, (e.g. rear A/C climate unit for third row of seats).