Checking cooling output - vehicles without high-voltage system — AUDI

🧭 Before you start

Prepare the car: ambient above 15 °C, cabin sealed, dash vents open, engine running. Using the diagnostic tester, confirm the compressor switches on (N280 current above 0.3 A, rising pressure from G395) after setting Auto, cold and dash-vent airflow. Select recirculation, raise engine speed to 2000 rpm and compare the G263 evaporator temperature with the graph, checking the sender itself if values are not reached.

Fits: Audi A5 (8T, 2007–2016), Audi Q5 (8R, 2008–2017), Audi A5 Cabriolet (8F), Audi A4 B8 (8K, 2007–2015); platform code 83

• Special tools named: VAS 5051

Don't miss

• Do not test below 15 °C ambient; the readings will not be meaningful.
• Close every door, window, sunroof, bonnet and rear lid, and open all dash vents.
• Confirm N280 specified and actual current both exceed 0.3 A before timing anything.
• Hold engine speed at 2000 rpm with recirculation on while reading G263.
• If targets are missed, verify the G263 sender reading before blaming the refrigerant circuit.

Written for this job from the workshop steps below · TorqFix editorial.

📋 Procedure

1. Measure ambient temperature (it must be over 15 °C).
2. Close doors, bonnet, windows, sun roof and rear lid.
3. Open all dash panel vents.
4. Start engine.
5. Switch off air conditioner compressor ("“ECON”" mode set on air conditioner operating and display unit, Climatronic control unit J255, indicator lamp in AC or A/C button off).

6. Start Guided Fault Finding for air conditioner Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").
7. In "“Read measured value block”" function, select display group with measured values for activation of air conditioner compressor and pressure in refrigerant circuit and read out measured values Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). [Note: On the absolute pressure scale, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute and 0 bar gauge pressure. On the scales of most pressure gauges, 0 bar gauge pressure corresponds to an absolute pressure of 1 bar (can be seen from -1 mark below 0).Depending on the version of the air conditioner operating and display unit (Climatronic control unit J255), the measured value block may only display values as whole numbers. The display fluctuates between two values if the measured pressure is between the two.The pressure in the refrigerant circuit depends on the ambient temperature. Due to the radiation of heat by components (e.g. radiator), the pressure displayed when the engine is warm is slightly higher than that given for the corresponding ambient temperature.If the pressure displayed is below that indicated in the table, check the signal of the refrigerant pressure and temperature sender G395Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). If no fault is found at the G395, there is not enough refrigerant in the circuit. Take the vehicle to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel Air conditioner with refrigerant R134a87General notes on air conditioning systems.]
8. Switch on air conditioner compressor by selecting "“Auto”" mode on air conditioner operating and display unit (Climatronic control unit J255) (indicator lamps in AUTO button(s) and AC or A/C button on).
9. Use rotary control(s) of air conditioner operating and display unit (Climatronic control unit J255) to set air conditioner to "“cold”" (for driver's and passenger's side).
10. On vehicles with a "“deluxe”" air conditioner, set potentiometer for rear temperature selection G538 to "“Cold”" (fitted in vent of rear centre console).
11. Use rotary control(s) of air conditioner operating and display unit (Climatronic control unit J255) to set air outflow direction to "“dash panel vents”" (for driver's and passenger's side). [Note: The indicator lamp(s) in the AUTO button(s) goes/go out when the air flow direction and/or the fresh air blower speed is/are altered manually.The maximum possible fresh air blower speed depends on various factors (coolant temperature, vehicle's electrical system voltage etc.).]
12. In the "“Read measured value block”" function, read out the specified current with which the air conditioner compressor regulating valve N280 is activated (a specified current above 0.3 A is displayed, the air conditioner compressor should be switched on) Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). [Note: The specified current is calculated by the air conditioner operating and display unit (Climatronic control unit J255). The request is transmitted via the data bus to the onboard supply control unit J519Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").]
13. In the "“Read measured value block”" function, read out the actual current with which the air conditioner compressor regulating valve N280 is activated (an actual current above 0.3 A is displayed, the air conditioner compressor is switched on) Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). [Note: If the measured value block shows no or insufficient current, check activation of air conditioner compressor regulating valve N280.The N280 is activated by the air conditioner operating and display unit (Climatronic control unit J255) via the onboard supply control unit J519. The activation of N280 is displayed in the measured value block of J519Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").The actual current flowing via the air conditioner compressor regulating valve N280 is measured by the onboard supply control unit J519 and transmitted via the data bus to the air conditioner operating and display unit (Climatronic control unit J255) Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").]
14. In the "“Read measured value block”" function, read out the pressure in the refrigerant circuit measured by the refrigerant pressure and temperature sender G395. The pressure displayed increases to above the value when the air conditioner compressor is switched off Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). [Note: If pressure displayed in measured value block does not change and activation of air conditioner compressor is OK, refer to Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding"). Check again whether the air conditioner compressor is really being driven and the air conditioner compressor regulating valve N280 is being activated. If the compressor is being driven and N280 is being activated, there is a fault in the refrigerant circuit. Take the vehicle to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel Air conditioner with refrigerant R134a87General notes on air conditioning systems. There may be problems with the control of the air conditioner compressor. Inform the workshop of the problem detected.The air conditioner compressor regulating valve N280 is activated by the air conditioner operating and display unit (Climatronic control unit J255) via N280 so that the temperature of the air downstream of the evaporator reaches the specified value (approx. 2 to 5 °C).After starting the vehicle, a value above 0.55 A is displayed depending on the measured temperature, engine speed and electrical system voltage. As soon as the temperature measured by the evaporator output temperature sender G263 approaches the specified value, activation is cancelled and the compressor output thus reduced.Under certain operating conditions, residual moisture in the refrigerant circuit may lead to the formation of ice at the air conditioner compressor regulating valve N280 (and at the expansion valve). Such ice formation impedes the control of the air conditioner compressor. The evaporator is cooled down too much and ices up. An iced-up evaporator may cause various problems .]
15. Press button for air recirculation mode on air conditioner operating and display unit (Climatronic control unit J255); symbol for "“air recirculation mode”" in air recirculation button lights up.
16. Set engine speed to 2000 rpm (start of time measurement).
17. In "“Read measured value block”" function, read out measured value for evaporator output temperature sender G263Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").
18. Compare measured value displayed (for G263) to values in graph. [Note: If required values are not attained, check measured value for evaporator output temperature sender G263. To do so, compare the measured value displayed for G263 to the measured values of the centre vent temperature sender G191 ("“basic”" version) / front left chest vent temperature sensor G385 ("“deluxe”" version).If the measured value for G263 only differs slightly from the measured value for G191 / G385, perform the measures to be taken if the readout does not match the specification .If the measured value for G263 is higher than the measured value for G191 or G385, check that the evaporator output temperature sender G263 is properly installed and perform the electrical checks for this sender Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").One way to check whether the air conditioner is working is by feeling the refrigerant lines: the "“low-pressure side”" refrigerant line (thick line between quick-release coupling and air conditioner compressor) cools down and the "“high-pressure side”" refrigerant line (thin line between condenser and quick-release coupling) becomes warm .]

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