Test Sequence
-- Disconnect the connector -B- from the A/C Compressor Regulator Valve -N280- -A-.
-- Using an adapter cable, re-establish the connection between the connector -A- and the connector -B- on the A/C Compressor Regulator Valve -N280-.
Depending on the A/C compressor version (with or without the A/C Clutch -N25-), different adapter cables are to be used. The Vehicle Diagnostic Tester - Test Adapter - 3 Pin:VAS5257 is used, for example, on an A/C compressor without an A/C Clutch -N25- and the Vehicle Diagnostic Tester - Test Adapter - 2 Pin:VAS5256 is used on an A/C compressor with an A/C Clutch -N25-. If no suitable adapter is available, the connection between the connector -A- and the connector -B- can be established using components from the Connector Test Set:VAG1594D .
However an adapter cable can also be used for this test. To do so, use, for example, one 2-pin connector each -A and B- (part number 1J0 973 702 and 1J0 973 802 and related terminal contacts), two commercially available sockets for banana connectors -C- and two wires with 0.5 mm 2 diameter on an A/C compressor with an A/C Clutch -N25-.
The A/C Compressor Regulator Valve -N280- is activated by the Vehicle Electrical System Control Module -J519- at the request of the Climatronic Control Module -J255- A/C display and control head using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Wiring Diagram.
The above illustration shows an A/C compressor without A/C Clutch -N25- where the 2-pin connector -A- leading to the vehicle wiring harness is attached directly to the A/C Compressor Regulator Valve -N280- (connector -B-). Depending on the version of the A/C compressor, the connector -B- may also have a short wire.
The A/C Compressor Regulator Valve -N280- activation is displayed in the Vehicle Electrical System Control Module -J519- measured values block. The maximum control current depends on the version of the Climatronic Control Module -J255- display and control head using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Wiring Diagram.
The measured current that flows over the A/C Compressor Regulator Valve -N280- is displayed in the measured values block for the Climatronic Control Module -J255- A/C display and control head and in the measured values block for the Vehicle Electrical System Control Module -J519- using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function
If the required actual current is not flowing over the A/C Compressor Regulator Valve -N280-, check the Vehicle Electrical System Control Module -J519- positive and ground connections and the wire connections between the Vehicle Electrical System Control Module -J519- and the A/C Compressor Regulator Valve -N280- for short circuit, contact resistance and interchanged wires according to the wiring diagram. Refer to Wiring Diagram.
-- Connect the probe to the adapter cables.
-- Measuring lead (signal wire) to terminal -2- of connector -B-
-- Measuring lead (shielding, Ground) to terminal -1- of connector -B-
For an A/C compressor with a different connector (for example, a 3-pin connector on an A/C compressor with an A/C Clutch -N25-), note the connector assignment when connecting the measuring cables. Refer to Wiring Diagram.
-- Select operating mode Test Instruments: DSO (Digital Storage Oscilloscope) on the Vehicle Diagnostic Tester.
-- Select 5 V/Div = 0.5 ms/Div (5 volts DC and 0.5 milliseconds per unit)
-- Start the engine.
-- Set the temperature preset to maximum cooling output on the Climatronic Control Module -J255- A/C display and control head.
-- Switch the activation of the A/C Compressor Regulator Valve -N280- on and off by pressing the AC (or A/C ) button (with an indicator lamp when the A/C compressor is on) on the Climatronic Control Module -J255- A/C display and control head
Shown on screen of oscilloscope, depending on setting of Climatronic Control Module -J255- A/C display and control head:
-- There is no square-wave signal when "OFF" or "AC off" mode is selected (indicator lamp in the "AC" or the A/C button does not illuminate) (the A/C Compressor Regulator Valve -N280- is not activated).
-- In operating mode "Auto" and "AC on" (indicator lamps in buttons come on) and temperature preselect for maximum cooling output, a square wave signal with an impulse width -A- between 75% and 100% (the control valve is activated).
The illustration shows a signal with a duty cycle of approximately 80%.
The impulse width -A- depends on the desired cooling output, electrical system voltage, etc. (over the width of region -A-, the current is regulated via the A/C Compressor Regulator Valve -N280- by the Vehicle Electrical System Control Module -J519- based on the request from the Climatronic Control Module -J255- A/C display and control head).
The signal distance -B- is always two milliseconds (corresponds to frequency of 500 Hertz).
The duty cycle is determined by the ratio of impulse width -A- and signal distance -B-.
-- The impulse width of the square-wave signal changes depending on the Climatronic Control Module -J255- A/C display and control head setting and the measured ambient influences (duty cycle between 100% and larger than 30%; the A/C Compressor Regulator Valve -N280- is activated so the compressor output necessary to reach the specified temperatures is achieved).
Whenever the mode is set to "Auto", and "AC on" (the indicator lamp in the buttons light up), and the temperature preset is set to "Lo", the A/C Compressor Regulator Valve -N280- is activated so that the maximum permissible current of approximately 0.65 A flows over the A/C Compressor Regulator Valve -N280- (maximum A/C compressor output).
In control mode, actuation time is governed by required cooling output and vehicle electrical system voltage, for example. It is however always of sufficient duration to achieve a mean current of 0.3 A.