Checking activation signal for air conditioning system compressor regulating valve N280 — AUDI

🧭 Before you start

Setup is ignition off, the control unit connected, the compressor connector unplugged and the adapter cable fitted in between with the probe on contact (2) for signal and contact (1) for screen. The diagnostic tester is put into DSO mode at 5 V/div DC and 0.5 ms/div, the engine started and the Climatronic set to Lo on both sides. Pressing Auto and Econ switches the valve on and off: no square wave in OFF or Econ, a square wave with a 75% to 100% pulse width in Auto at Lo. In normal control mode the pulse width floats above 30% depending on cooling demand and system voltage.

Fits: Audi A4 Cabriolet B6/B7 (8H), Audi A4 B6/B7 (8E)

Don't miss

• Signal wire to contact (2), screen to contact (1); get the probe the right way round.
• Lo on both driver and passenger sides in Auto mode; otherwise the valve is not at maximum.
• Expect a 2 ms period (500 Hz); only the pulse width changes with demand.
• Econ or OFF must show no square wave; a trace there points at the control side.
• Full-output current is approx. 0.6 to 0.8 A; the mean in control mode is never below 0.3 A.

Written for this job from the workshop steps below · TorqFix editorial.

📋 Procedure

1. Switch off ignition.
2. Connect up operating and display unit, Climatronic control unit J255 to vehicle wiring harness.
3. Unplug connector at air conditioner compressor (to air conditioning system compressor regulating valve N280).
4. Use adapter cable from adapter setV.A.G 1594C to re-establish connection between connector (A) and connector (B) at compressor (to air conditioning system compressor regulating valve N280). [Note: Use can also be made for this test of an improvised adapter cable. This requires, for example, one connector (A) and (B) each (with part number 1J0 973 702 and 1J0 973 802 and the corresponding plug contacts), two commercially available sockets for banana plugs (C) and two wires with a cross section of 0.5 mm2.]
5. Connect probeVAS 5051/8 to adapter leads.

6. Test lead (signal wire) to contact (2)
7. Test lead (screen, earth) to contact (1)
8. On vehicle diagnostic, testing and information systemVAS 5051A, set measurement mode: "“DSO”" (Digital Storage Oscilloscope).
9. Settings 5V/div DC, 0.5 ms/div (5 V DC and 0.5 milliseconds per unit)
10. Start engine.
11. On operating and display unit, Climatronic control unit J255, select "“Lo”" temperature setting for driver's and front passenger's side.
12. On operating and display unit, Climatronic control unit J255, press buttons "“Auto”" and "“Econ”" to activate and deactivate air conditioning system compressor regulating valve N280.
13. In "“OFF”" or "“Econ”" mode: No square-wave signal (air conditioning system compressor regulating valve N280 is not actuated)
14. In "“Auto”" mode and "“Lo”" temperature setting: Square-wave signal with pulse width (A) between 75% and 100% (air conditioning system compressor regulating valve N280 is actuated) [Note: The illustration shows a signal with a ratio of approx. 80%.The pulse width (A) is governed by the required cooling output, electrical system voltage etc. (over width of area (A), current is controlled via air conditioning system compressor regulating valve N280 by operating and display unit, Climatronic control unit J255).The signal distance (B) is always 2 milliseconds (corresponding to a frequency of 500 Hertz).The duty cycle is derived from the ratio of pulse width (A) to signal distance (B).]
15. The setting on the operating and display unit, Climatronic control unit J255 and measured ambient influences govern the pulse width of the square-wave signal (signal ratio between 100% and greater than 30%, air conditioning system compressor regulating valve N280 is actuated such that the compressor output required to obtain the specified temperatures is achieved). [Note: In "“Auto”" mode with "“Lo”" temperature setting, the air conditioning system compressor regulating valve N280 is actuated such that the max. perm. current of approx. 0.6 to 0.8 A flows via the air conditioning system compressor regulating valve N280 (maximum compressor output).In control mode, the actuation time is governed by the 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.]

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