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Fault localisation in the event of ice formation at the evaporator > < Checking cooling output

A4 Mk3

Measures to be taken if readout does not match specification (required cooling output is not attained)
   
Measures to be taken if readout does not match specification (required cooling output is not attained)
–  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 → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Repeat the cooling output test → Chapter.
–  Heed the compressor actuation displays during the cooling output test.
–  Air conditioner compressor deactivated during cooling output test (specified speed drops below 1500 rpm)?
↓
yes
↓
↓
no
↓
Continuation → Anchor Deactivation of air conditioner compressor.
l  Increase in pressure in refrigerant circuit during cooling output test?
 ↓
yes
↓
↓
no
↓
 Continuation → Anchor Increase in pressure in refrigerant circuit.
–  In the „Reading measured values“ function of the battery regulation control unit -J840-, select the display with the measured values for actuation of the refrigerant shut-off valve 1 for hybrid battery -N516- using the → "Guided Fault Finding" function of the vehicle diagnostic, testing and information system VAS 5051.
–  If -N516- is actuated, deal with the issue that caused it to be actuated.
–  If the air conditioner compressor is actuated and -N516- is not actuated, 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.
–  Inform the workshop of the problem found (possibly insufficient refrigerant in circuit, -N516- is blocked or electrical air conditioner compressor -V470- is defective).

Continuation of test: „Actuation of air conditioner compressor is deactivated“
   
–  Deactivation of air conditioner compressor during cooling output test by air conditioner operating and display unit, Climatronic control unit -J255- (by battery regulation control unit -J840- or control unit for air conditioning compressor -J842-), drop in specified speed to below 1500 rpm?
↓
yes
↓
↓
no
↓
–  Interrogate the event recorder of -J255-, -J840- and -J842-.
–  Air conditioner compressor deactivated during cooling output test by -J840- or -J842- (just actual speed drops below 1500 rpm)?
–  Eliminate the faults displayed and erase the event recorder.
–  Read out the measured value block with the compressor shut-off criteria of -J255- and eliminate the cause of deactivation → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Repeat the cooling output test → Chapter.
–  Interrogate the event recorder of -J840- and -J842-, eliminate the fault displayed and erase the event recorder. → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  In the measured value block of -J840- and -J842-, read out the displays in which the measured values for actuation of the electrical air conditioner compressor -V470- are indicated.
–  Check actuation of -V470- by -J842- and eliminate the cause of deactivation → Chapter.
–  Repeat the cooling output test → Chapter.

Continuation of test: „Increase in pressure in refrigerant circuit“
   
–  Open the front lid.
–  Repeat the cooling output test → Chapter.
–  Read out the pressure in the refrigerant circuit from the measured value block of the air conditioner operating and display unit, Climatronic control unit -J255- → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
l  The radiator fan(s) (radiator fan -V7- and radiator fan 2 -V177-) run(s) during the cooling output test. The speed is governed by the coolant temperature and the pressure in the refrigerant circuit; this is detemined by the engine control unit. Or the radiator fans are switched in as soon as the pressure in the refrigerant circuit exceeds approx. 9 bar?
↓
yes
↓
↓
no
↓
–  Read out the measured value blocks displaying the „pressure in the refrigerant circuit“ and „actuation of the radiator fans“ → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
l  Operation of radiator fan(s) at higher speed as pressure in refrigerant circuit increases in line with request from -J255-?
–  Check actuation of the radiator fan(s), e.g. in the „Final control diagnosis“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Service the actuation system for the radiator fan(s).
–  Repeat the cooling output test → Chapter.
↓
yes
↓
↓
no
↓
 
–  In the „Reading measured values“ function of the battery regulation control unit -J840-, select the display with the measured values for actuation of the refrigerant shut-off valve 1 for hybrid battery -N516- using the → "Guided Fault Finding" function of the vehicle diagnostic, testing and information system VAS 5051.
–  If -N516- is actuated, deal with the issue that caused it to be actuated.
–  If the air conditioner compressor is actuated and -N516- is not actuated, 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.
–  Inform the workshop of the problem found (possibly insufficient refrigerant in circuit, -N516- is blocked or electrical air conditioner compressor -V470- is defective).
–  Check actuation of the radiator fans, e.g. in the „Final control diagnosis“ function → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Service the actuation system for the radiator fan(s).
–  Repeat the cooling output test → Chapter.

  Note
t  The pressure in the refrigerant circuit is governed by various factors of influence. As a general rule, however, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25 °C. Under extreme usage conditions (e.g. in hot countries with high ambient temperatures, „stop and go traffic“ and high relative humidity), the extremely high cooling output involved may also result in pressures of up to 31 bar.
t  At ambient temperatures below 25 °C the pressure in the refrigerant circuit does not usually rise above 16 bar (the radiator fan(s) run(s) and cool(s) the condenser).
t  The measured value of the refrigerant pressure and temperature sender -G395- is used by the operating and display unit, Climatronic control unit -J255- to calculate the pressure in the refrigerant circuit, which it then displays → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  At absolute pressures of less than approx. 1.8 bar and greater than approx. 32 bar, the operating and display unit, Climatronic control unit -J255- does not switch on the air conditioner compressor (the control unit for air conditioning compressor -J842- and thus the electrical air conditioner compressor -V470- are not actuated). The air conditioner compressor is only switched on again once the absolute pressure has risen above 1.8 bar or dropped below 16 bar.
t  Further information on the pressure in the refrigerant circuit can be found in the guided fault-finding routine → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
t  To prevent abrupt air conditioner compressor shut-off on account of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the air conditioner operating and display unit, Climatronic control unit -J255- as soon as the pressure in the refrigerant circuit exceeds approx. 30 bar (absolute) (full compressor output is not released again until the pressure has dropped below 27 bar) or the coolant temperature exceeds 115 °C (complete shutdown at 118 °C).
   

Fault localisation in the event of ice formation at the evaporator > < Checking cooling output