Audi Q7: Malfunction Determination in Case of Deviation from Target Value (Required Cooling Output of Front A/C System not Achieved)
- In the "read measured values" function, select the display group with the measured values for the A/C compressor activation and the refrigerant circuit pressure. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Repeat the cooling output test. Refer to → Chapter "Cooling Output, Checking".
- During the cooling output test, pay attention to the display for the compressor actuation.
- Is the activation of the A/C Compressor Regulator Valve -N280- switched off during the cooling output test (is the specified and/or the actual current less than 0.35 A)?
Continuation. The A/C compressor activation is switched off.
- Did the pressure in refrigerant circuit increase during the cooling output test?
Continuation. Increase in pressure in the refrigerant circuit.
- Check one more time if the compressor shaft is actually being driven and if the A/C Compressor Regulator Valve -N280- is really being actuated.
- If the A/C compressor is driven and the A/C Compressor Regulator Valve -N280- is actuated, then bring the vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel. Refer to → Refrigerant R134a Servicing; Rep. Gr.87; A/C System, General Information.
- Bring the detected problems to the attention of the workshop.
Test Continuation "The A/C compressor actuation is switched off"
- Was the activation of the A/C Compressor Regulator Valve -N280- switched off during the cooling output test by the Front A/C Display Control Head -E87- or from the Vehicle Electrical System Control Module -J519-, are the target current and the actual current less than 0.35 A?
- Check the event memory and the relevant measured values of the Front A/C Display Control Head -E87- and the Vehicle Electrical System Control Module -J519- and correct the reason for the deactivation. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Is the activation of the A/C Compressor Regulator Valve -N280- switched off by the Front A/C Display Control Head -E87- or the Vehicle Electrical System Control Module -J519- during the cooling output test (the actual current is less than 0.35 A)?
- Check the DTC memory of the Front A/C Display Control Head -E87- and the Vehicle Electrical System Control Module -J519-, correct any displayed malfunctions, and erase the event memory. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" Function.
- Repeat the cooling output test.
- In the "read measured values" function of the Guided Fault Finding of the Front A/C Display Control Head -E87- and the Vehicle Electrical System Control Module -J519-, read out the displays in which the measured values for the activation of the A/C Compressor Regulator Valve -N280- are displayed.
- Check the actuation of the A/C Compressor Regulator Valve -N280- by the Vehicle Electrical System Control Module -J519- and correct the cause of the switching off.
- Repeat the cooling output test.
Continuation of test: "Pressure in refrigerant circuit increases"
- Open the engine hood.
- Repeat the cooling output test. Refer to → Chapter "Cooling Output, Checking".
- From the measured values of the Front A/C Display Control Head -E87-, read out the pressure in the refrigerant circuit and the activation of the radiator fans. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Is/are the radiator fan(s) (Radiator Fan -V7- and Radiator Fan 2 -V177-) running during the cooling output test according to the activation? The RPM depends on the coolant temperature and on the refrigerant circuit pressure, it is determined by the engine control module. Or the radiator fans switch off as soon as the refrigerant circuit pressure exceeds approximately 9 bar (130.52 psi)?
- Read the measured values with the display for the "refrigerant circuit pressure" and the "radiator fan activation". Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" Function.
- Is/are the radiator fan(s) running at a higher speed when the pressure in the refrigerant circuit increases according to the request from the Front A/C Display Control Head -E87- (the target and actual values may deviate from one another)?
- Bring the vehicle to a workshop that has the necessary tools and where the work can be performed by qualified personnel.
- Bring the detected problems to the attention of the workshop.
- Check the activation of the radiator fan(s), for example, in the "output diagnostic test mode" function. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- The request to activate the radiator fans is made by the Front A/C Display Control Head -E87-, while the actual activation is performed by other control modules. Therefore, the actual value for the activation of the radiator fans can deviate from the required target value. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Repair the activation of the radiator fan(s).
- Repeat the cooling output test.
- Check the activation of the radiator fan(s), for example, in the "output diagnostic test mode" function. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Service the activation of the radiator fan(s).
- Repeat the cooling output test.
Note
- The pressure in the refrigerant circuit depends on several factors. However, at an ambient temperature between 20 to 25 ºC (68 to 77 ºF) the pressure should not exceed more than 20 bar (290.07 psi). Under extreme conditions (for example, "stop and go traffic" at a high ambient temperature and high relative humidity), pressures up to 31 bar (449.61 psi) may occur due to the extremely high cooling output.
- At ambient temperatures below 25 ºC (77 ºF), pressure in refrigerant circuit does not normally exceed 16 bar (232.06 psi) (radiator fans run and cool condenser).
- Via the measured value of the High Pressure Sensor -G65- the Front A/C Display Control Head -E87- calculates the refrigerant circuit pressure and shows this. Refer to Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- At an absolute pressure of less than approximately 1.8 bar (26.1 psi) or greater than approximately 32 bar (464.12 psi), the Front A/C Display Control Head -E87- does not switch on the A/C compressor (the A/C Compressor Regulator Valve -N280- is not activated). The A/C compressor is only switched on once the absolute pressure becomes greater than 1.8 bar (26.1 psi) or less than 16 bar (232.06 psi).
- Additional information on the refrigerant circuit pressure can be found. Refer to Vehicle Diagnostic Tester.
- To prevent abrupt A/C compressor shutoff due to excessive pressure in refrigerant circuit or an excessive coolant temperature, the Front A/C Display Control Head -E87- regulates the A/C compressor output. As soon as the refrigerant circuit pressure exceeds 30 bar (435.11 psi) (absolute pressure), full A/C compressor output is only enabled again after pressure has become less than 27 bar (391.60 psi), or the coolant temperature exceeds 115 ℃ (it is switched off completely at 118 ℃).
