Refrigerant Circuit with Expansion Valve

WARNING: This page does not describe the selected car, but rather 17 other vehicles, including the 2009 Audi S4, 2009 Audi A4, 2008 Audi S4, 2008 Audi RS 4, and 2008 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

HP (HD) High pressure side of refrigerant circuit

LP (ND) Low pressure side of refrigerant circuit

Component	Refrigerant state	Pressure (bar)	Temperature in degrees Celsius
1 Evaporator, from inlet to outlet	Vapor	approx. 1.2 bar 1	approx. -7 ° C 2
2 Expansion valve	Liquid, released as vapor	approx. 14 bar	approx. + 55 ° C (HP- side), reduces to -7 ° C (LP-side)
3 High pressure switch / high pressure sensor	Liquid	approx. 14 bar	approx. + 55 ° C
4 Service connection, HP (HD) side and 5 fluid reservoir	Liquid	approx. 14 bar	approx. + 55 ° C
6 Condenser	Gas (at inlet) to vapor to liquid (at outlet)	approx. 14 bar	From approx. + 65 ° C (at input) to approx. + 55 ° C (at outlet)
7 pressure relief valve and 8 compressor, HP (HD) side	Gas	approx. 14 bar	approx. + 65 ° C
9 Compressor, LP (ND) side	Gas	approx. 1.2 bar 1	approx. -1 ° C 2
10 Pre-volume (not present in all vehicles) and 11 Service connection, LP (ND) side	Gas	approx. 1.2 bar 1	approx. -1 ° C 2

* 1 - The pressure in a refrigerant circuit with regulating compressor is maintained at approx. 2 bar absolute pressure (corresponds to approx. 1 bar positive pressure) despite varying heat transfer and fluctuating engine speeds. This however only applies within the output range of the compressor. If the output limits of the compressor are exceeded, the pressure will rise → Refrigerant Circuit, Checking Pressures with A/C Service Station .

* 2 - The temperature in a refrigerant circuit with regulating compressor is maintained within the regulating range of the compressor despite varying heat transfer and fluctuating engine speeds. This however only applies within the output range of the compressor. If the output limits of the compressor are exceeded, the temperature will rise → Refrigerant Circuit, Checking Pressures with A/C Service Station .

NOTE:

Non self-regulating compressors are switched off by the relevant control module via the A/C Compressor Regulator Valve N280 at evaporator temperatures below 0 C.
On vehicles with A/C Compressor Regulator Valve N280 the pressure on the low pressure side is altered by actuating the valve.
Temperature and pressure in the refrigerant circuit in vehicles with two evaporators and two expansion valves correspond to those in vehicles with only one evaporator and one expansion valve (parallel switching).

Arrows show direction of refrigerant flow.

HD- High Pressure (HP) side of refrigerant circuit.

ND- Low Pressure (LP) side of refrigerant circuit.

Fig 1: Refrigerant Circuit With Expansion Valve Overview

Courtesy of VOLKSWAGEN UNITED STATES, INC.

1 - Evaporator

2 - Expansion valve

3 - High pressure switch / high pressure sensor

Different versions depending on vehicle

4 - Service connection, HP (HD) side

5 - Receiver

Different versions depending on vehicle

6 - Condenser

7 - Pressure relief valve

8 - Compressor, HP (HD) side

9 - Compressor, LP (ND) side

10 - Pre-volume

Not present on all vehicles

11 - Service connection, valve LP (ND)