Checking cooling output - vehicles with high-voltage system — AUDI

🧭 Before you start

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

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• Measure ambient temperature (it must be over 15 °C).

📋 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. ⚠ When working on a vehicle with the ignition switched on or while the drive system is active, the engine can start unexpectedly and exhaust fumes can cause a health hazard in closed rooms. Moving parts can trap or draw in parts of the body and/or clothing (safety hazard). Before switching on the ignition, perform the following steps:Move selector lever to position PActivate parking brake Switch off ignitionOpen bonnetConnect battery charger (e.g. VAS 5095A) to jump-start connections of 12 V electrical system Switch on ignition — To minimise the number of automatic engine starts when the vehicle's drive system is active (READY) during test and measurement work, charge the vehicle batteries e.g. with the battery charger 60AVAS 5904 in battery standby mode Electrical system27Battery; Charging battery and Electrical system93General warning instructions for work on the high-voltage system. [Note: The status of the drive system (READY) is shown by the control unit in dash panel insert J285 via the "“power meter”".Activating vehicle drive system (check "READY" display in control unit in dash panel insert J285) Owner's ManualMove the selector lever to position "“P”" and activate the parking brake before performing test and measurement work for which the ignition must be switched on but where the vehicle's drive system does not need to be active.]
5. Ignition switched on and drive system active (READY), engine only starts or runs if e.g. drive battery A2 is not sufficiently charged.

6. 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).
7. Start Guided Fault Finding for air conditioner Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").
8. In "“Read measured value block”" function, select display groups with measured values for activation of air conditioner compressor and pressure in refrigerant circuit and read out measured values (on vehicles with electrical air conditioner compressor V470 the values are displayed in different measured value blocks) Vehicle diagnostic, testing and information system ("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 displays for the activation of the air conditioner compressor differ. For a mechanically driven air conditioner compressor, the tester displays the specified and actual current for activation of the air conditioner compressor regulating valve N280. For an electrical air conditioner compressor V470, the specified and actual speed of V470, which are transmitted by the control unit for air conditioning compressor J842, are displayed in a different measured value block Vehicle diagnostic, testing and information system ("Guided Fault Finding").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.]
9. 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).
10. 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).
11. On vehicles with a "“deluxe”" air conditioner, set potentiometer for rear temperature selection G538 to "“Cold”" (fitted in vent of rear centre console).
12. 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.).]
13. In the "“Read measured value block”" function, read out the speed at which the electrical air conditioner compressor V470 is activated by the control unit for air conditioning compressor J842 (the display will show a speed greater than 800 rpm: air conditioner compressor is running) Vehicle diagnostic, testing and information system ("Guided Fault Finding"). [Note: The specified speed is calculated by the air conditioner operating and display unit (Climatronic control unit J255). The request is transmitted via the data bus to the control unit for air conditioning compressor J842Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding").When driving, the air conditioner compressor operates over a speed range of 800 to 8600 rpm.When the vehicle is stationary or only moving slowly (up to a speed of approx. 45 km/h), the air conditioner compressor is not activated at the maximum specified speed (of approx. 8500 rpm); the air conditioner compressor speed is limited to approx. 5000 rpm.At an air conditioner compressor speed of 5000 rpm, with a very high ambient temperature (in excess of 35° C) and a high fresh air blower speed (unfavourable ambient conditions), the output (delivery volume) of the air conditioner compressor is not always sufficient at first to reduce the temperature of the air downstream of the evaporator to the specified value. One way of checking the control action of the air conditioner compressor under these conditions is to activate the fresh air blower with only approx. 40 % of the maximum voltage and to check the temperature at reduced fresh air blower speed Vehicle diagnostic tester in "“Guided Fault Finding”" mode for air conditioner and battery regulation.If an insufficient speed, or no speed at all, is displayed in the measured value block (a speed of less than 4000 rpm although the required temperature of the air downstream of the evaporator has still not been reached), check the activation of the electrical air conditioner compressor V470 by the control unit for air conditioning compressor J842Vehicle 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 the pressure displayed in the measured value block does not change and the activation of the compressor is OK (Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding")), 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 is activated by the control unit for air conditioning compressor J842 (when requested by the air conditioner operating and display unit, Climatronic control unit J255) in such a way that the temperature of the air downstream of the evaporator reaches the specified value (approx. 2 to 5 °C).After the engine is started, the air conditioner compressor is activated at a speed greater than 3000 rpm 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 expansion valve for the evaporator in the air conditioning unit. This ice formation can impair the control function of the expansion valve / air conditioner compressor. The evaporator is insufficiently or excessively cooled and may ice up. An iced-up evaporator may cause various problems .This vehicle is fitted with 2 evaporators (one in the air conditioning unit and one in the battery cooling module). If the measured temperature corresponds to or is below the specified value at one evaporator but the required specified value is not attained at the other evaporator, the system is controlled as follows: The battery regulation control unit J840 activates the electric air conditioner compressor at a higher speed via the power and control electronics for electric driveJX1 and the control unit for air conditioning compressor J842. This causes the cooling output of the air conditioner to increase and the pressure on the low-pressure side and the evaporator temperature to drop. If the temperature set value is then not reached at one evaporator, J840 activates the refrigerant shut-off valve 1 for hybrid battery N516 or the refrigerant shut-off valve 2 for hybrid battery N517 such that refrigerant no longer flows through the evaporator which is too cold Vehicle diagnostic tester, "“Guided Fault Finding”" function for air conditionerAs the cooling output of the evaporator in the battery cooling module is considerably less than that of the evaporator in the air conditioning unit, the required temperature may still be reached in the battery cooling module when there is insufficient refrigerant in the circuit, but the required temperature will no longer be reached at the evaporator in the air conditioning unit (although the air conditioner compressor is being activated at a higher speed).]
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. 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").
17. 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 .] [Note: The refrigerant shut-off valve 1 for hybrid battery N516 installed in the refrigerant line to the expansion valve upstream of the evaporator in the air conditioning unit is open when it is not activated. If this valve is activated or blocked, refrigerant cannot flow through to the expansion valve; check operation using Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding") (for J840).] [Note: The refrigerant shut-off valve 2 for hybrid battery N517 attached to the expansion valve of the battery cooling module is closed when not activated; check operation using Vehicle diagnostic, testing and information system VAS 5051 ("Guided Fault Finding") (for J840).]

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