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A/C Compressor-On-Signal & A/C Compressor Cut-Out, Checking: Testing

  1. Start engine and let idle.
  2. Select "READ MEASURING VALUE BLOCK" function 08 using (VAG 1551) Scan Tool and input display group number. See READING/MEASURING VALUE BLOCK (FUNCTION 08) under OUTPUT DIAGNOSTIC TEST MODES (DTM) in SELF-DIAGNOSTICS article.
  3. Observe display values in channel 4. Display position 1 indicates if A/C compressor is ON: Must read 0.
  4. Display position 2 indicates if A/C system is ON: Must read 0.
  5. Display position 3: Must remain blank.
  6. Switch ON A/C, selecting lowest temperature and highest blower speed.
  7. Observe display values.
  8. Position 1 must change from 0 to 1.
  9. Position 2 must change from 0 to 1.
  10. Observe display while performing the following: Press accelerator pedal to floor quickly, then release immediately.
  11. Position 1 must change from 1 to 0, for several seconds. If NO, connect (VAG 1598) test box, using (VAG 1598/5) adapter cable to ECM. See CONNECTING VAG 1598 TEST BOX .
  12. Connect (US 1115) LED tester between terminal No. 19 (ground) and terminal No. 6.
  13. Allow engine to idle. Switch ON A/C, selecting lowest temperature/highest blower speed. LED tester must light up, within 1-6 seconds.
  14. Apply accelerator pedal quickly, then release immediately. LED tester must go out for a few seconds.
  15. If NO (for either step): Switch ignition OFF (stop engine). Wait at least 30 seconds before disconnecting adapter cable from ECM.
  16. Check wiring for breaks/opens between ECM terminal No. 6 (terminal 6 of test box), and A/C, using wiring diagram. Also, see Figure.
  17. If wiring is Okay, check function of A/C clutch control module J153.
  18. Check function of A/C control head -E87-.
  19. If A/C control module and A/C control head are Okay, replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.
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