A/C refrigerant system cooling performance, testing: Notes

WARNING: This page is about a different car, the 2004 Audi S4, 2004 Audi A4, 2003 Audi A4, and 2002 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.

The pressure in the refrigerant circuit depends on various factors. However, at an ambient temperature between 20 to 25° C the pressure should not exceed more than 20 bar. Due to high coolant performance, pressures up to 31 bar may occur under extreme operating conditions (e.g. in southern countries with high ambient temperatures, "stop and go" traffic and high humidity).
The pressure in the refrigerant system does not increase above 16 bar at ambient temperatures lower than 25° C (the coolant fan runs and cools the condenser).
Via the duty cycle (READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 001: , display field "3") the A/C Control Head -E87- calculates the pressure in the refrigerant circuit.
When the duty cycle is smaller than 12.5% (corresponds to approx.: 1.8 bar absolute pressure) and greater than 87.5% (corresponds to approx.: 32 bar absolute pressure) the compressor is not switched on by the A/C Control Head -E87- (A/C Compressor Regulator Valve -N280- is not activated). The compressor will be switched on again when duty cycle is greater than 12.5% (correspond 1.8 bar absolute pressure) or smaller than 48% (corresponds to 16 bar absolute pressure).
If the pressure in the refrigerant circuit or the engine coolant temperature is too high, the A/C Control Head -E87- regulates the compressor performance (to avoid sudden compressor cut-off):

- When pressure in refrigerant circuit exceeds 30 bar (absolute pressure) (the complete compressor output is only switched again after the pressure is less than 27 bar).
- As soon as the coolant temperature reaches 115° C (at 118° C compressor is switched off completely).

If the pressure in the refrigerant circuit was greater than 32 bar (duty cycle greater than 87.5%) the compressor is switched on again by the A/C control head -E87-, if pressure drops below 29 bar (duty cycle is less than 84%).
Additional notes on pressures in the refrigerant circuit, see READ MEASURING VALUE BLOCK (FUNCTION 08) , DISPLAY GROUP 001: .