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Display group "002” > < Measured value blocks from display group "001” to display group "010”

A4 Cabriolet Mk2

Display group “001”
Display group “001”
Air conditioning system compressor regulating valve -N280- and high-pressure sender -G65-
  Note
t  In the event of a compressor shutoff criterion → Chapter, the air conditioning system compressor regulating valve -N280- cannot be actuated even during final control diagnosis ( → Chapter).
t  If no pressure signal from the high-pressure sender -G65- is detected, the air conditioning system compressor regulating valve -N280- must not be actuated.
   
Display zoneSignificanceExplanatory notes
1Measured control current for air conditioning system compressor regulating valve -N280- (in amps)
l  Current flowing via air conditioning system compressor regulating valve -N280-
 
t  Display = less than 0.050 A
–  Compressor switched off
 
 
t  Display = 0.300 A to 0.650 A (up to 0.8 A)
–  Compressor in control mode; control current is governed by cooling output required
 

  Note
t  Display zone “1” indicates the current flowing via the air conditioning system compressor regulating valve -N280-.
t  The current is calculated by the operating and display unit, Climatronic control unit -J255- and is governed by the required cooling output, the operating mode selected (set) for the operating and display unit, Climatronic control unit -J255- and the electrical system voltage. The regulating valve can however only operate reliably if there is a specified minimum current flow (0.3 A for the regulating valves fitted at present).
t  Full air conditioning system compressor regulating valve -N280- actuation results in a maximum current of at present approx. 0.65 A (up to 0.8 A) depending on vehicle electrical system voltage and the version of the operating and display unit, Climatronic control unit -J255- (calculated, regulated and limited by operating and display unit, Climatronic control unit -J255-).
t  If the pressure in the refrigerant circuit (display zones “3” and “4”) does not change when the engine is running despite the air conditioning system compressor regulating valve -N280- being actuated with maximum current, check the pulley or the drive unit at the compressor. The compressor must be driven (if the overload safeguard has been tripped, the pulley turns, for example, but the compressor is not driven) → Chapter.
   
Display zoneSignificanceExplanatory notes
2Duty cycle for actuation of air conditioning system compressor regulating valve -N280- (in %)
l  Time component of air conditioning system compressor regulating valve -N280- actuation
 
t  Display = 0%
–  Compressor switched off
 
 
t  Display = 30....40% to 100%
–  Compressor in control mode, actuation time is governed by cooling output required, operating mode selected and electrical system voltage. The minimum actuation time is however that required to achieve a mean current flow of 0.3 A and the maximum time is such that a mean current of 0.65 A (0.8 A) is not exceeded.
 

  Note
t  The duty cycle for the period during which current can actually flow is indicated in display zone “2”.
t  The operating and display unit, Climatronic control unit -J255- employs a frequency of 500 Hz (500 Hertz = 500 activation pulses per second). The duty cycle indicates the proportion of the ON time per pulse.
t  The activation signal can be checked for example using the vehicle diagnostic, testing and information system -VAS 5051A- (“Measurement” function) → Chapter.
t  The duty cycle is selected by the operating and display unit, Climatronic control unit -J255- such that the evaporator outflow temperature sender -G263- attains the specified evaporator temperature, which is influenced by various factors → Chapter.
t  If a fault is detected at the evaporator outflow temperature sender -G263-, the operating and display unit, Climatronic control unit -J255- switches to emergency operation and the air conditioning system compressor regulating valve -N280- is then only actuated with a maximum control current specified by the software of the operating and display unit, Climatronic control unit -J255-. The maximum control current is governed by the version of the operating and display unit, Climatronic control unit -J255- and may be between approx. 0.3 A and 0.5 A for the operating and display units, Climatronic control unit -J255- fitted at present (the cooling output of the air conditioner is thus reduced and the cooling effect is no longer sufficient at higher temperatures).
   
Display zoneSignificanceExplanatory notes
3Ratio for pressure signal from high-pressure sender -G65- (in %)
l  Time component of positive signal from high-pressure sender -G65-
 
t  Display = 0....5%
–  Open circuit in wiring between high-pressure sender -G65- and operating and display unit, Climatronic control unit -J255-
–  Open circuit in power supply or earth connection to high-pressure sender -G65-
–  High-pressure sender -G65- defective
 
 
t  Display = 5% to 12 %
–  Insufficient pressure in refrigerant circuit (system empty)
–  High-pressure sender -G65- defective
 
 
t  Display = 12 % to 87.5%
–  Pressure in refrigerant circuit in permissible range
l  If a ratio of less than 16.5 % is displayed at an ambient temperature above 20° C, the measured value of the high-pressure sender -G65- is not OK or there is not enough refrigerant in the circuit
 
t  Display = greater than 87.5 ...90%
–  Pressure in refrigerant circuit too high
–  Actuation of radiator fan(s) -V7- not OK
–  High-pressure sender -G65- defective
–  Radiator and/or condenser contaminated
–  Fault in refrigerant circuit
 
 
t  Display = 90....100%
–  Short to positive (or earth) in wiring between high-pressure sender -G65- and operating and display unit, Climatronic control unit -J255-
–  Open circuit in power supply or earth connection to high-pressure sender -G65-
–  High-pressure sender -G65- defective
 

  Note
t  The ratio for the period during which the signal is actually applied is indicated in display zone “3”.
t  The operating and display unit, Climatronic control unit -J255- uses the ratio to calculate the pressure in the refrigerant circuit. The calculated pressure is indicated in display zone “4”.
t  If the ratio is less than 12 % (corresponding to approx. 1.8 bar absolute pressure) and greater than 87.5% (corresponding to approx. 32 bar absolute pressure), the operating and display unit, Climatronic control unit -J255- does not switch on the compressor (the air conditioning system compressor regulating valve -N280- is not actuated). The compressor is only re-activated once the ratio exceeds 15 % (corresponding to absolute pressure of 2.6 bar) or drops below 48% (corresponding to absolute pressure of 16 bar).
t  To prevent abrupt compressor shutoff on account of excessive pressure in the refrigerant circuit or excessive coolant temperature, the compressor output is reduced by the operating and display unit, Climatronic control unit -J255-:
t  - As soon as the pressure in the refrigerant circuit exceeds 30 bar (absolute) (full compressor output is not released again until pressure has dropped below 16 bar)
t  - As soon as the coolant temperature exceeds 115° C (full shutdown at 118° C)
t  Depending on the ratio, the operating and display unit, Climatronic control unit -J255- transmits a signal via the convenience data bus system to the relevant engine control unit, thus causing it to act on the radiator fan control unit -J293- to switch the radiator fan(s) -V7-.
t  Depending on the version of the operating and display unit, Climatronic control unit -J255-, the radiator fan is either switched on immediately in air conditioning mode when the compressor is activated or the radiator fan is only actuated on exceeding a pressure of approx. 9 bar in the refrigerant circuit.
t  At absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure thus corresponds to roughly 1 bar absolute. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from “-1” mark below “0”).
t  The pressure in the refrigerant circuit and thus the ratio are governed by various factors. As a general rule, however, the pressure will not exceed 20 bar (absolute) with maximum compressor output and 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 30 bar (absolute).
t  The high-pressure sender -G65- operates with a frequency of 50 Hz (50 Hertz = 50 activation pulses per second). The signal ratio indicates the proportion of the ON time per pulse.
t  The activation signal can be checked for example using the vehicle diagnostic, testing and information system -VAS 5051A- (“Measurement” function) → Chapter (Checking signal from high-pressure sender -G65-).
t  The signal generated by the high-pressure sender -G65- is also used to control the engine (the torque required to drive the compressor is governed by the pressure in the refrigerant circuit). Depending on the engine control unit version, the signal is displayed as signal ratio in the measured value block of the relevant engine control unit.
t  The signal transmitted at a refrigerant circuit pressure of approx. 5 to 6 bar absolute corresponds to a signal ratio of approx. 22%, which is achieved with the compressor not running, at an ambient temperature of 20 °C and with the refrigerant circuit properly charged.
   
Display zoneSignificanceExplanatory notes
4Pressure in refrigerant circuit (in bar absolute)
t  Display = less than 2.6 bar
–  Insufficient pressure in refrigerant circuit (system empty)
–  High-pressure sender -G65- defective
l  The pressure is calculated by way of the signal ratio indicated in display zone “3” by the operating and display unit, Climatronic control unit -J255-.
 
t  Display = 2.6 bar to 29 bar
–  Pressure in refrigerant circuit in permissible range
l  If a pressure of less than 4 bar is displayed at an ambient temperature above 20° C, the measured value of the high-pressure sender -G65- is not OK or there is not enough refrigerant in the circuit
 
t  Display = greater than 29 bar (also for brief periods)
–  Pressure in refrigerant circuit too high
–  Actuation of radiator fan(s) -V7- not OK
–  High-pressure sender -G65- defective
–  Radiator and/or condenser contaminated
–  Fault in refrigerant circuit
 

  Note
t  Also heed the notes on display zone “3”.
t  By way of the signal ration (display zone “3”), the operating and display unit, Climatronic control unit -J255- calculates the pressure in the refrigerant circuit.
t  If the 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, Climatronic control unit -J255- only recognises a fault in the refrigerant circuit at pressures of less than 1.8 bar (attained at -12 °C). The high-pressure sender -G65- is however no longer interrogated at this temperature.
t  If the pressure in the refrigerant circuit (display zones “3” and “4”) does not change when the engine is running despite the air conditioning system compressor regulating valve -N280- being actuated with maximum current, check the pulley or the drive unit at the compressor. The compressor must be driven (if the overload safeguard has been tripped, the pulley turns, for example, but the compressor is not driven) → Chapter.
   

Display group "002” > < Measured value blocks from display group "001” to display group "010”