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Warning notices for working on vehicles with a high-voltage system > < Block diagram of air distribution system

A5

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 regulating valve -N280- deactivated during cooling output test (specified and/or actual control current drops below 0.50 A)?
↓
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.
–  Check again whether the compressor shaft is actually being driven and -N280- actuated.
–  If the air conditioner compressor is being driven and -N280- 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 problems encountered.

   
Continuation of test: „Actuation of air conditioner compressor is deactivated“
–  Air conditioner compressor regulating valve -N280- deactivated during cooling output test by air conditioner operating and display unit, Climatronic control unit -J255- (specified current and actual current drop below 0.50 A)?
↓
yes
↓
↓
no
↓
–  Interrogate the event recorder of the air conditioner operating and display unit, Climatronic control unit -J255-.
–  -N280- deactivated during cooling output test by onboard supply control unit -J519- (just actual current drops below 0.50 A)?
–  Eliminate the faults displayed and erase the event recorder.
–  Read out the measured value block with the compressor shut-off criteria of the air conditioner operating and display unit, Climatronic control unit -J255- and eliminate the cause of shut-off → "Guided fault-finding" function of vehicle diagnostic, testing and information system VAS 5051.
–  Repeat the cooling output test → Chapter.
–  Interrogate the event recorder of -J519-, 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 -J519-, read out the display groups in which the measured values for actuation of -N280- are indicated.
–  Check actuation of -N280- by -J519- 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. Speed is governed by coolant temperature and pressure in refrigerant circuit (determined by 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
↓
 
–  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 this workshop of the problems encountered.
–  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 air conditioner compressor regulating valve -N280- is 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).
   

Warning notices for working on vehicles with a high-voltage system > < Block diagram of air distribution system