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Display group 002: > < Display groups 001 to 005

A2

Display group 001:
Display group 001:
Air conditioner compressor regulating valve -N280- and high-pressure sender -G65-
  Note
t  In the event of a compressor shut-off criterion (see display group “002”), the air conditioner compressor regulating valve -N280- cannot be actuated, even during final control diagnosis ( → Chapter).
t  If there is no pressure signal detected from the high-pressure sender -G65-, the air conditioner compressor regulating valve -N280- may not be actuated.
   
Display zoneMeaningExplanatory Notes
1Measured control current for air conditioner compressor regulating valve -N280- (in amps)
l  Current flowing via the air conditioner compressor regulating valve -N280-.
 
t  Display = less than 0.050 A
–  Compressor switched off
 
 
t  Display = 0.3 A to 0.8 A
–  Compressor in control mode; the control current is governed by the required refrigeration capacity
 

  Note
t  Display zone “1” shows the intensity of current that flows via the air conditioner compressor regulating valve -N280-.
t  The current intensity is calculated by the operating and display unit for air conditioner/Climatronic -E87-. It is dependent on the required refrigeration capacity, the selected operating and display unit for air conditioner/Climatronic -E87- mode and the vehicle system voltage. For safe regulation on the part of the regulating valve, however, a prescribed minimum current must flow. For the regulating valves installed at present this is 0.3 A.
t  If the air conditioner compressor regulating valve -N280- is fully actuated, there is a maximum current of approx. 0.8 A or 0.65 A depending on the vehicle system voltage and the version of the operating and display unit for air conditioner/Climatronic -E87- in use.
   
Display zoneMeaningExplanatory Notes
2Signal ratio for actuation of the air conditioner compressor regulating valve -N280- (in %)
l  Time proportion of actuation of the air conditioning system compressor regulating valve -N280-
 
t  Display = 0%
–  Compressor switched off
 
 
t  Display = 30....40% to 100%
–  Compressor in control mode; the actuation time depends on the required refrigeration capacity, the mode selected and the vehicle system voltage. However, the actuation time is at least long enough for a mean current of 0.3 A to flow and no longer than required for a mean current of approx. 0.8 A or 0.65 A not to be exceeded (depending on the version of the operating and display unit for air conditioner/Climatronic -E87-).
 

  Note
t  The signal ratio for the time during which the current can actually flow is displayed in display zone “2”.
t  The operating frequency for the operating and display unit for air conditioner/Climatronic -E87- is 500 Hz (500 Hertz = 500 cut-in pulses per second). The signal ratio indicates the proportion of cut-in time per pulse.
t  The cut-in signal can be tested with the vehicle diagnostic, testing and information system -VAS 5051- in the measuring instrument function, for example → Chapter.
t  The signal ratio is selected by operating and display unit for air conditioner/Climatronic -E87- in such a way that the target temperature of the evaporator, which is dependent upon various factors, is achieved on the evaporator outlet temperature sender -G263- → Chapter.
t  If a defect is detected in the evaporator outlet temperature sender -G263-, the operating and display unit for air conditioner/Climatronic -E87- switches to emergency running and the air conditioner compressor regulating valve -N280- is only actuated with a max. control current which is specified by the software for the operating and display unit for air conditioner/Climatronic -E87-. The maximum control current is governed by the version of operating and display unit for air conditioner/Climatronic -E87- in use. With the operating and display unit for air conditioner/Climatronic -E87- currently installed, this may be approx. 0.3 A to 0.5 A (as a result of which, the refrigeration capacity of the air conditioner is reduced and, at higher temperatures, the cooling performance may no longer prove to be adequate).
   
Display zoneMeaningExplanatory Notes
3Signal ratio for the pressure signal from the high-pressure sender -G65- (in %)
l  Time proportion of the positive signal from the high-pressure sender -G65-
 
t  Display = 0...0.5%
–  Open circuit in the wiring between the high-pressure sender -G65- and the operating and display unit for air conditioner/Climatronic -E87-
–  Open circuit in the power supply or in the earth connection to high-pressure sender -G65-
–  High-pressure sender -G65- is defective
 
 
t  Display = 5% to 12%
–  Pressure in the refrigerant circuit is too low (system empty)
–  High-pressure sender -G65- is defective
 
 
t  Display = 12% to 87.5%
–  Pressure in the refrigerant circuit is within the permissible range.
l  If, at an ambient temperature above 20° C, a signal ratio of below 16.5 % is displayed, the measured value of the high-pressure sender -G65- is not OK or there is too little refrigerant in the circuit
 
t  Display = greater than 87.5 ...90%
–  Pressure in the refrigerant circuit too high.
–  Actuation of radiator fans -V7- is not OK.
–  High-pressure sender -G65- is defective
–  Radiator and/or condenser are dirty
–  Fault in the refrigerant circuit
 
 
t  Display = 90....100%
–  Short circuit to earth in the wiring between the high-pressure sender -G65- and the operating and display unit for air conditioner/Climatronic -E87-
–  Open circuit in the power supply or in the earth connection to the high-pressure sender -G65-
–  High-pressure sender -G65- is defective
 

  Note
t  The signal ratio for the time is displayed in display zone “3” whilst the signal is actually present.
t  The operating and display unit for air conditioner/Climatronic -E87- calculates the pressure in the refrigerant circuit via the signal ratio. The calculated pressure is displayed in display zone “4”.
t  At a signal ratio of less than 12.5% (corresponds to approx. 1.5 bar absolute) and greater than 87.5% (corresponds to approx. 32 bar absolute), the operating and display unit for air conditioner/Climatronic -E87- does not switch on the compressor (the air conditioner compressor regulating valve -N280- is not actuated). The compressor is only reactivated once the signal ratio exceeds 12.5% (corresponding to an absolute pressure of 1.5 bar) or drops below 84% (corresponding to an absolute pressure of 29 bar).
t  In order to prevent abrupt compressor shut-off on account of excessive pressure in the refrigerant circuit or an excessive coolant temperature, the compressor output is reduced by the operating and display unit for air conditioner/Climatronic -E87-:
t  - As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) (full compressor output is not released again until the pressure has dropped below 27 bar).
t  - As soon as the coolant temperature exceeds 115° C (it is shut down completely at 118° C).
t  At a signal ratio of approx. 47% (equivalent to an absolute pressure of 16 bar in the refrigerant circuit), the operating and display unit for air conditioner/Climatronic -E87- sends a signal to the control unit for the radiator fans -J293-, thereby switching the radiator fan -V7- to speed 2. The signal remains on until the signal ratio has fallen below approx. 40% (equivalent to an absolute pressure of approx. 13 bar).
t  An absolute pressure of 0 bar represents an absolute vacuum. Therefore normal ambient pressure is equivalent to approx. 1 bar absolute. On the dials of most pressure gauges 0 bar is equivalent to an absolute pressure of one bar (recognisable by the datum -1 below 0).
t  The pressure in the refrigerant circuit and therefore the signal ratio depends on various factors. In general, however, at maximum compressor output and an ambient temperature of 20 to 25 °C, the pressure should not exceed 20 bar (absolute). Under extreme conditions of use (e.g. in hot countries with high ambient temperatures, “stop and go traffic” and high relative humidity), the extremely high refrigeration capacity involved may also result in pressures of up to 30 bar (absolute).
t  The high-pressure sender operates at a frequency of 50 Hz (50 Hertz = 50 cut-in pulses per second). The signal ratio indicates the proportion of cut-in time per pulse.
t  The cut-in signal from the high-pressure sender -G65- can be tested, for example, with the vehicle diagnostic, testing and information system -VAS 5051- in the measuring instrument function → Chapter.
t  The signal generated by the high-pressure sender -G65- is also used for engine control (the required compressor drive torque is governed by the refrigerant circuit pressure). Depending on the engine control unit version, the signal is displayed as a signal ratio in the measured value block.
t  The signal transmitted at a refrigerant circuit pressure of approx. 6 bar absolute is equivalent to a signal ratio of approx. 22% (automatic adjustment with the compressor at a standstill, at an ambient temperature of 20 °C, and with a properly filled refrigerant circuit).
   
Display zoneMeaningExplanatory Notes
4Pressure in the refrigerant circuit (in bar absolute)
l  The pressure is calculated via the signal ratio shown in display zone 3 by the operating and display unit for air conditioner/Climatronic -E87-.
 
t  Display = less than 2.6 bar
–  Pressure in the refrigerant circuit is too low (system empty)
–  High-pressure sender -G65- is defective
 
 
t  Display = 2.6 bar to 29 bar
–  Pressure in the refrigerant circuit is within the permissible range
l  If, at an ambient temperature above 20 °C, a pressure of below 4 bar is displayed, the measured value from the high-pressure sender -G65- is not OK or there is too little refrigerant in the circuit
 
t  Display = greater than 29 bar (also for brief periods)
–  Pressure in the refrigerant circuit is too high.
–  Actuation of radiator fans -V7- is not OK.
–  High-pressure sender -G65- is defective
–  Radiator and/or condenser are dirty
–  Fault in the refrigerant circuit
 

  Note
t  Heed the notes on display zone “3”.
t  The operating and display unit for air conditioner/Climatronic -E87- calculates the pressure in the refrigerant circuit via the signal ratio (display zone “3”).
t  If a refrigerant circuit has been properly charged, the pressure settles at 2.6 bar at a temperature of -3 C°. To avoid a fault being stored at low temperatures, the operating and display unit for air conditioner/Climatronic -E87- only detects a fault in the refrigerant circuit at pressures below 1.8 bar (attained at -12 °C). However, the high-pressure sender -G65- is no longer interrogated at this temperature.
   

Display group 002: > < Display groups 001 to 005