Section 31 (Air Conditioning (Refrigerant R134A Refrigerant Circuit)): Glossary

Different designations, the Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- is installed inside the refrigerant line to the evaporator inside the A/C unit on the Audi Q5 hybrid. If the Hybrid Battery Refrigerant Shut-Off Valve 1 Hybrid Battery Refrigerant Shut-Off Valve 1 -N516- is activated by the electronics, it is closed and does not allow any refrigerant to flow toward the evaporator in the A/C unit. The Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- is, for example, is attached directly to the expansion valve on the evaporator inside the battery cooling module on the Audi Q5 hybrid. When the Hybrid Battery Refrigerant Shut-Off Valve 2 Hybrid Battery Refrigerant Shut-Off Valve 2 -N517- is activated by the electronics, it is open and allows the refrigerant to flow through the expansion valve to the evaporator in the battery cooling module. Refer to Refrigerant Circuit (vehicle-specific Service Information).

The reservoir collects the mixture from the evaporator to ensure that the compressor only draws in dry refrigerant in gas form. Moisture which has entered the refrigerant circuit during repairs will be collected by a filter (dryer cartridge) in the reservoir. The reservoir is always installed with the restrictor. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Refrigerant is non-flammable. It actually has a fire resistant or fire extinguishing effect.

Audi does not approve the use of chemicals (stop leak additives) to seal leaks in the refrigerant circuit. Chemical materials to seal leaks in the refrigerant circuit react with air or the moisture in the surrounding air and form deposits in the refrigerant circuit (and in the A/C service station) that lead to malfunctions in the valves and other components that come into contact with such chemicals. These deposits cannot be removed completely from the components.

Other identification for a heater core. For example, heat energy is extracted from the flowing coolant in a chiller due to the evaporation of the refrigerant. Refer to Refrigerant Circuit .

Is the pressure acting on the surface of a liquid. Vapor pressure is dependent on temperature.

The restrictor creates a constriction. This constriction restricts the flow rate, thus governing the quantity of refrigerant for the evaporator. The restrictor also divides the refrigerant circuit into high and low-pressure side.

The high-pressure gauge measures the pressure distributed evenly from the compressor outlet via the condenser to the constriction (restrictor, expansion valve) when the air conditioning system is switched on. The low-pressure gauge measures the pressure distributed evenly from the constriction (restrictor, expansion valve) via the evaporator to the inlet of the compressor when the air conditioning system is switched on.

Different designations, the A/C Pressure/Temperature Sensor 2 -G826- is for example installed on the Audi Q7 e-tron in the refrigerant line to the A/C compressor. These sensors measure the temperature and the refrigerant pressure at the component location and transmit their measured values to the connected control module. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Switches the radiator fan to the appropriate speed and the A/C compressor "off" if there is a loss of refrigerant or excess pressure. Refer to Refrigerant Circuit (vehicle-specific Service Information).

The electric A/C compressor is driven by a control module and an electric motor (on the Audi Q5 hybrid: A/C Compressor Control Module -J842- and Electrical A/C Compressor -V470-). The A/C compressor draws in the refrigerant gas from the evaporator, compresses it and sends it to the condenser. Refer to Refrigerant Circuit (vehicle-specific Service Information).

-101.6 °C (-150.9 °F) for R134a at normal atmospheric pressure (1 bar (14.5 psi)).

The expansion valve atomizes the flowing refrigerant and controls the flow rate so that the vapor is only gaseous at the evaporator output, depending on the heat transmission.

The receiver/dryer collects the droplets of liquid and conveys them in a continuous stream to the expansion valve, as otherwise the expansion valve would not be able to fill the evaporator properly. Moisture which has entered the refrigerant circuit during repairs will be collected by a filter (dryer cartridge) in the reservoir. The receiver/dryer is installed with the expansion valve. Refer to Refrigerant Circuit (vehicle-specific Service Information).

A fluid collector collects and stores the liquid refrigerant (for example, on the Audi Q7 e-tron when the A/C system is operating as the heat pump) which is not necessary for some operating conditions. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Trade names also applying to refrigerants which are not to be used in vehicles.

To prevent a canister from being overfilled, the regulations regarding compressed gases specify how many kilograms of refrigerant may be added to a canister per liter of internal volume. The product of multiplying this "charge factor" by the internal volume of the canister is the permissible capacity. For refrigerant the figure is 1.15 kg (2.54 lbs) / l.

A control module uses the sensor pulses (4 per compressor revolution) and the engine speed to calculate the belt slip. If the belt slip exceeds a specified value, the A/C compressor is switched off by the control module via the A/C clutch.

Different names and versions. When voltage is applied, the A/C Pressure/Temperature Sensor -G395- exchanges information with the control module via the air conditioner databus system ("LIN bus"). The relevant control module uses this information to calculate the pressure and the temperature in the refrigerant circuit. Any faults detected are then signaled to the control module. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Different names and versions. When voltage is applied, the Refrigerant Circuit Pressure Sensor -G805- exchanges information with the control module via the A/C system data bus ("LIN bus"). The relevant control module uses this information to calculate the pressure in the refrigerant circuit. Any faults detected are then signaled to the control module. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Different names and versions. The High Pressure Sensor -G65- generates a square-wave signal or data telegram when voltage is applied. This signal changes along with the pressure in the system. The downstream control modules (radiator fan control module, engine control module, A/C display control head, etc.) use this signal to calculate the pressure in the refrigerant circuit and to actuate the A/C clutch, A/C Compressor Regulator Valve -N280-, radiator fans and motor accordingly. Refer to Refrigerant Circuit (vehicle-specific Service Information).

This poses a danger to people if the electric current has a certain voltage and a resulting current strength depending on the length of time. The voltages are divided into classes; if the operating voltage for a vehicle system (DC or AC) exceeds a specific value (for example, 50 V at AC or 120 V at DC), this is a high-voltage system. Only certified technician may work on the high-voltage system, who are especially trained. Refer to the appropriate service information for more information.

Hybrid vehicles are vehicles with two drive systems, on these vehicles an internal combustion engine and an electric drive motor.

Attracts moisture (for example: refrigerant oil).

In the inner heat exchanger, the refrigerant in the high pressure side (fluid and warm) flows opposite the flow direction of the refrigerant in the low pressure side (gas or vapor and cold). Due to the difference in temperature, the high pressure side refrigerant emits energy to the low pressure side refrigerant, which increases the efficiency of the A/C system. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Special synthetic refrigerant oils, for example, polyalkylene glycol (PAG) oil, are used in conjunction with refrigerant R134a A/C systems. These refrigerant oils mix with the refrigerant, and do not the damage materials of the R134a A/C system. The refrigerant oil flows with the refrigerant through the refrigerant circuit to assure that the lubricating film in the A/C compressor does not break down under the existing pressures and temperatures.

Thus one must work with a substance that boils easily, which is described here as refrigerant. The refrigerant R134a used is Tetrafluorethane. It boils at -26.5°C (-15.7 °F) at normal atmospheric pressure (1 bar (14.5 psi) absolute pressure).

Different names and versions. The Refrigerant Temperature Sensor -G454- (a temperature-dependent resistor) determines the temperature in the refrigerant circuit; it is installed in the high pressure line near the A/C compressor, for example. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Refer to the A/C service station

The condenser diverts heat away from the compressed refrigerant gas to the surrounding air.

The A/C compressor extracts the refrigerant gas from the evaporator, compresses it and sends it to the condenser.

The A/C service station is used to drain refrigerant, to clean it, to separate it from refrigerant oil, to flush and to fill the refrigerant circuit. For the currently available service stations, refer to the Parts Information (Tools; Special Tools and Equipment: A/C and Heating).

The refrigerant R134a remains chemically stable up to a gas pressure of 39.5 bar (572.9 psi) (corresponding to a temperature of 101 °C (213.8 °F)), above this temperature, the refrigerant decomposes.

This is used to straighten bent condenser slats.

Minor leaks can only be traced by way of an electronic leak detector or by first rendering them visible in UV light, for example using a special additive. Start up the leak detector in line with relevant operating instructions.

The flow of refrigerant in the second evaporator is switched on or off by the shut-off valve.

This makes the connection between the belt pulley and the A/C compressor drive axle.

The battery in this unit reduces the nitrogen vapor pressure via the pressure gauges. The vapor pressure in the nitrogen cylinder is approximately 50 bar (725.19 psi) at workshop temperature. The battery can also be used to check for leaks in the refrigerant circuit.

The power unit drives the mechanical A/C compressor via a belt or shaft. The A/C compressor extracts the refrigerant gas from the evaporator, compresses it and sends it to the condenser.

This is used to document the amount of refrigerant used. A record sheet no longer needs to be kept in the EU due to a provision by the European Parliament in 2005. Other provisions may apply in countries that are not members of the EU.

The NTC- sensor can be, for example, a temperature-dependent resistor which has a decreasing resistance value with increasing temperature.

These rings seal off the connection points between individual components of the refrigerant circuit.

With an externally regulated compressor, the regulating valve is actuated by the control module to control the pressure on the low-pressure side and thus the evaporator temperature.

When working on the refrigerant circuit, always observe the generally valid safety precautions and the pressure canister regulations.

This refers to the conversion of an air conditioning system from refrigerant R12 to R134a.

The check valve only lets refrigerant flow through in one direction. It makes sure that the refrigerant depending on the operating condition of the A/C system only can flow in one direction. On the Audi Q7 e-tron, they ensure that the refrigerant cannot flow into certain components during heat pump operation and is no longer available for operation. Refer to Refrigerant Circuit (vehicle-specific Service Information).

Quick-release connections connect and secure the refrigerant lines at the connecting points. Special tools are needed to disconnect the connections.

This is found on air conditioning systems converted from R12 to R134a refrigerant. It is not suitable for R134a, as the refrigerant does not mix 100 % with the refrigerant oil.

These are valves installed in the connections, for example for service work in the refrigerant circuit.

It boils at -26.5 °C (-15.7 °F) at normal atmospheric pressure (1 bar (14.5 psi)).

Cleaning the refrigerant circuit using an A/C service station and a flushing device with refrigerant R134a (opposite the direction of refrigerant flow when the A/C system is operating).

Is used to flush refrigerant circuits.

The temperature switch determines the temperature between the cooling fins of the evaporator to stop the evaporator icing up.

Temperature-dependent resistors are available in various construction types: in a "NTC- resistor" the resistance value decreases with increasing temperature; in a "PTC- resistor" the resistance value increases with increasing temperature.

tk stands for critical temperature (also known as critical point). This means, above the critical temperature there is no longer a boundary between liquid and gas. A substance above its critical temperature is always gaseous. At temperatures below the critical temperature, all types of refrigerant in pressure canisters exhibit both a liquid and a gas phase, for example 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.

The Technical Rules for Compressed Gases (TRG), Technical Rules for Hazardous Substances (TRGS) and the Technical Rules for Operational Safety (TRBS) describe the state of technology, occupational safety and industrial hygiene as well as other substantiated industrial science knowledge for the provision and use of work equipment such as systems requiring monitoring during use or involving activities with hazardous substances. The provided technical rules apply to Germany. Different regulations and laws may apply in other countries.

The GWP indicates warming effect that 1 kg (2.2 lbs) of this material has on the surface temperature of a planet (for example, the earth) over a 100 year period in comparison to that of 1 kg (2.2 lbs) of carbon dioxide. The GWP value of refrigerant R134a is 1300. The GWP value of carbon dioxide is 1.

The valve opens at approximately 38 bar (551.14 psi). The valves (depending on the A/C system) of some compressors are fitted with a disc that breaks off when the valve is activated.

Refrigerant and refrigerant oil escape when there is a leak in the refrigerant circuit. Generally, this oil remains in the vicinity of the leaking area. A small amount of fluorescent fluid must be added to the refrigerant circuit so the oil becomes visible under UV light. This fluid (PAG oil with an additive that lights up under UV light) is added into the refrigerant circuit and distributes itself with the refrigerant oil when the A/C system is switched on.

The UV-leak detection lamp emits UV light at a certain wave length. This light makes the additive that was added to the refrigerant circuit visible. When there is a leak, the additive escapes from the refrigerant circuit with the refrigerant and refrigerant oil and generally remains in the area of the leak.

The liquid refrigerant evaporates in the evaporator pipe coils. The heat required for this is extracted from the air flowing on the evaporator ribbing.

Water destroys the A/C system, because it forms acids when combined with other contaminants at high pressures and temperatures.

During heat pump operation, energy from the surrounding air (or from the high-voltage cooling system coolant on an Audi Q7 e-tron, for example) is captured via the A/C system refrigerant circuit and is used to heat the vehicle interior via the coolant in the engine coolant circuit. Refer to Refrigerant Circuit (vehicle-specific Service Information).

In a heater core the energy is transferred from one medium to another (for example in the climate control evaporator from the air flow on the refrigerant in the refrigerant circuit).