A/C Compressor Regulator Valve -N280-, Checking Switch-On Signal
Special Tools And Workshop Equipment Required
- Vehicle Diagnostic Tester
- Vehicle Diagnostic Tester - Test Adapter - 2 Pin :VAS5256 , Vehicle Diagnostic Tester - Test Adapter - 3 Pin :VAS5257 or Connector Test Set :VAG1594D
- Probe :VAS5051/8
The following describes the test an A/C compressor without an A/C Clutch -N25-. The test is to be performed in the same way for vehicles with a different compressor type or a different manufacturer.
However, for an A/C compressor with an A/C Clutch -N25-, a 3-pin connector may be installed. Refer to the appropriate Wiring Diagram(s).
Certain functions on the A/C Compressor Regulator Valve -N280- (for example, a stuck valve or a disruption in the coil) can lead to a complaint regarding the A/C compressor (A/C system doesn't cool, the evaporator ices over, etc.). If the cause is with the A/C Compressor Regulator Valve -N280- (and not the A/C compressor itself), the A/C compressor can be serviced by replacing the A/C Compressor Regulator Valve -N280-. Refer to COMPONENTS, REPLACING - R134a or COMPONENTS, REPLACING (R1234yf) .
The A/C Compressor Regulator Valve -N280- is not available as a replacement part for all A/C compressors. If the A/C Compressor Regulator Valve -N280- is not available as an individual A/C compressor part (different versions), then the entire A/C compressor must be replaced.
For an A/C compressor with an A/C Clutch -N25-, the connector terminals may need to be removed from the connector housing on the A/C Compressor Regulator Valve -N280- to replace the A/C Compressor Regulator Valve -N280-. Refer to COMPONENTS, REPLACING - R134a or COMPONENTS, REPLACING (R1234yf) .
Test Sequence
-- Remove the noise insulation. Refer to NOISE INSULATION, REMOVING AND INSTALLING / OVERVIEW - NOISE INSULATION .
-- Disconnect the connector -2-.
-- Using an adapter cable, re-establish the connection between the connector -2- and the A/C Compressor Regulator Valve -N280- -1-.
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 - 2 Pin :VAS5256 is used, for example, on an A/C compressor without an A/C Clutch -N25- and the Vehicle Diagnostic Tester - Test Adapter - 3 Pin :VAS5257 is used on an A/C compressor with an A/C Clutch -N25-. If no suitable adapter is available, the connection between the connector -1- and the connector -2- 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 activation of the A/C Compressor Regulator Valve -N280- and the current measured by the control head (Climatronic Control Module -J255- or the A/C Control Module -J301-), which flows via the A/C Compressor Regulator Valve -N280-, is displayed in the control head measured values. "Read the measured values" in the "Guided Fault Finding" . Refer to Vehicle Diagnostic Tester.
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 the appropriate Wiring Diagram(s).
-- Connect the :VAS5051/8 to the adapter cables.
- Measuring cable (signal wire) to contact "2" of connector -2-.
- Measuring cable (shielding, ground) to contact "1" of connector -2-.
-- Set the operating mode "measuring equipment" DSO (digital storage oscilloscope) on the Vehicle Diagnostic Tester.
-- Select the setting 5V/Div = 0.5 ms/Div (5 V DC and 0.5 milliseconds per unit).
-- Start the engine.
-- Set the temperature preset for the driver- and front passenger side to "Lo" on the A/C control head. By pressing the buttons Auto and AC , the activation of the A/C Compressor Regulator Valve -N280- is switched on and off.
-- Set the temperature knob to the "cold" stop on the control head. By pressing the button AC , the activation of the A/C Compressor Regulator Valve -N280- is switched on and off.
The following is displayed on the oscilloscope screen depending on the control head setting:
- There is no square-wave signal when "OFF" is selected (the indicator lamp in the A/C button does not turn on) (the A/C Compressor Regulator Valve -N280- is not activated).
- With "Auto" mode selected (only automatic climate control system) and the A/C
button pressed (indicator lamp in the A/C
button illuminates), there is a square-wave signal with an impulse width -A- between 75% and 100% (the A/C Compressor Regulator Valve -N280- is activated).
The illustration shows a signal with a duty cycle of approximately 80%.
The impulse width -A- is dependent on the desired cooling output, electrical system voltage, etc. (over the width of region -A-, the voltage is regulated via the A/C Compressor Regulator Valve -N280- by the Climatronic Control Module -J255- /A/C Control Module -J301- control head).
The signal distance -B- is always 2 milliseconds. This 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 (duty cycle between 100% and greater than 30%, the A/C Compressor Regulator Valve -N280- is activated so that the necessary compressor output is obtained to reach the specified temperatures) depending on the setting on the control head and the measured ambient influences.
With the setting, for example, "Auto" mode (automatic climate control system), "Lo" temperature setting and the A/C button pressed (indicator lamp in the A/C button illuminates), the A/C Compressor Regulator Valve -N280- is activated so that the maximum permissible current of approximately 0.65 A flows via the A/C Compressor Regulator Valve -N280- (maximum 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.