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Measures to be taken if readout does not match specification (required cooling output is not attained) > < Prerequisites for checking cooling output of air conditioner

A4 Mk3

Checking cooling output
Checking cooling output
Not on vehicles with a high-voltage system (hybrid vehicles)
Vehicles with a mechanically driven air conditioner compressor only
t  Requirements for checking cooling output satisfied → Chapter
–  Measure the ambient temperature (must be above 15 °C).
–  Close the doors, front lid, windows, sun roof and rear lid.
–  Open all dash panel vents.
–  Start the engine.
–  Switch off the air conditioner compressor („Econ“ mode set on air conditioner operating and display unit, Climatronic control unit -J255-, lamp in AC button not lit).
–  Start air conditioner guided fault-finding → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  In the „Reading measured value block“ function, select the display group with the measured values for actuation of the air conditioner compressor and the pressure in the refrigerant circuit and read out the measured values → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  The air conditioner compressor is switched off, a current of 0 A (amps) is displayed.
t  At the measured ambient temperature, the pressure in the refrigerant circuit is equal to or higher than the value in the table.
   
Ambient temperature in °CPressure displayed (in bar)
153.0
204.0
255.0
306.0
357.0

  Note
t  At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute and 0 bar pressure. On the scales of most pressure gauges, 0 bar pressure corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0).
t  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.
t  The pressure in the refrigerant circuit is governed by the ambient temperature. Due to the radiation of heat by components (e.g. the radiator), the pressure displayed with a warm engine is slightly higher than that given for the corresponding ambient temperature.
t  If the displayed pressure is lower than that given in the table, check the signal of the refrigerant pressure and temperature sender -G395- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051. If no fault is found at -G395-, there is not enough refrigerant in the circuit. The vehicle is to be taken to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a.
If the pressure in the refrigerant circuit is OK
–  Switch on the air conditioner compressor by selecting „Auto“ mode on the air conditioner operating and display unit, Climatronic control unit -J255- (lamp in AUTO button(s) and AC button lights).
–  Use the rotary control(s) of the air conditioner operating and display unit, Climatronic control unit -J255- to make „cold“ temperature setting (for the driver and passenger side).
–  On vehicles with an air conditioner of the „Deluxe“ type, set the potentiometer for rear temperature selection -G538- to „Cold“ (fitted in vent of rear centre console).
–  Use the rotary control(s) of the air conditioner operating and display unit, Climatronic control unit -J255- to set the air outflow direction to „dash panel vents“ (for the driver and passenger side).
  Note
t  The lamp in the AUTO button(s) goes out when the air outflow direction and/or the fresh air blower speed is/are altered manually.
t  The maximum possible fresh air blower speed depends on various ambient influences (coolant temperature, vehicle electrical system voltage etc.).
–  In the „Reading measured value block“ function, read out the specified current with which the air conditioner compressor regulating valve -N280- is actuated (a specified current greater than 0.3 A is displayed, the air conditioner compressor should be switched on) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
  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 -J519- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  In the „Reading measured value block“ function, read out the actual current with which the air conditioner compressor regulating valve -N280- is actuated (an actual current greater than 0.3 A is displayed, the air conditioner compressor is switched on) → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
  Note
t  If the measured value block shows no or insufficient current, check actuation of the air conditioner compressor regulating valve -N280- → Chapter.
t  -N280- is actuated by the air conditioner operating and display unit, Climatronic control unit -J255- by way of the onboard supply control unit -J519-. Actuation of -N280- is displayed in the measured value block of -J519- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  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- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  In the „Reading 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 with the air conditioner compressor switched off → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
  Note
t  If the pressure displayed in the measured value block does not change and actuation of the air conditioner compressor is OK → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051, Check again whether the air conditioner compressor is actually being driven and the air conditioner compressor regulating valve -N280- actuated. If the compressor is being driven and -N280- actuated, there is a fault in the refrigerant circuit. The vehicle is to be taken to a workshop equipped with the necessary tools where the work can be performed by appropriately qualified personnel → Air conditioner with refrigerant R134a (there may be problems with air conditioner compressor control). Inform the workshop of the problems encountered.
t  The air conditioner compressor regulating valve -N280- is actuated by the air conditioner operating and display unit, Climatronic control unit -J255- (via -N280-) such that the temperature of the air downstream of the evaporator reaches the specified value (approx. 2 to 5 °C).
t  After starting the vehicle, a value greater than 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, actuation is cancelled and the compressor output thus reduced.
t  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 air conditioner compressor control. The evaporator is excessively cooled and ices up. Icing-up of the evaporator may give rise to various problems → Chapter.
–  Press the air recirculation mode button on the air conditioner operating and display unit, Climatronic control unit -J255- (the symbol for „air recirculation mode“ in the air recirculation button lights).
–  Set the engine speed to 2000 rpm (start of time measurement).
–  In the „Reading measured value block“ function, read out the measured value of the evaporator output temperature sender -G263- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
   
–  Compare the measured value displayed (for -G263-) to the values in the graph.
A - Air temperature (downstream of evaporator) measured by the evaporator output temperature sender -G263-
B - Ambient temperature
C - Permissible tolerance range
Depending on the ambient temperature, the measured air temperature must be within the stated tolerance range -C- after 5 minutes.
  Note
t  If the required values are not attained, check the measured value of the 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) / the front left chest vent temperature sensor -G385- („Deluxe“ version).
t  If the measured value for -G263- only differs slightly from the measured value for -G191- / -G385-, perform "Measures to be taken if readout does not match specification" → Chapter.
t  If the measured value for -G263- is greater than the measured value for -G191- or -G385-, check for proper installation of the evaporator output temperature sender -G263- → Chapter and perform the electrical checks for this sender → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  Operation of the air conditioner can be seen for example from the fact that the „low-pressure end“ refrigerant line (thick line between quick-release coupling and air conditioner compressor) cools down and the „high-pressure end“ refrigerant line (thin line between condenser and quick-release coupling) becomes warm → Chapter.
The cooling output test is over if the measured value of the evaporator output temperature sender -G263- (and thus the cooling output of the air conditioner) is OK and there are no problems.
t  If the measured value of the evaporator output temperature sender -G263- (and thus the cooling output of the air conditioner) is not OK, perform the measures to be taken if the readout does not match the specification (the required cooling output is not attained) → Chapter.
t  If the measured value of the evaporator output temperature sender -G263- (and thus the cooling output of the air conditioner) is OK and there is a problem with excessively high or differing outflow temperatures, check actuation of the temperature flaps → Chapter.
  A87-10572

Measures to be taken if readout does not match specification (required cooling output is not attained) > < Prerequisites for checking cooling output of air conditioner