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HOMESERVICE MANUALSAUDI1998A4 AVANT QUATTRO, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)EXTERNAL PAGESDIFFERENT CARSECTION 16 (AUTOMATIC A/C-HEATER SYSTEMS)SYSTEM TESTSA/C PRESSURE SWITCH, A/C COMPRESSOR SIGNAL, ENGINE TEMPERATURE SIGNAL & INTERIOR TEMPERATURE SENSOR FAN
1998 Audi A4 Avant Quattro, Automatic

A/C Pressure Switch, A/C Compressor Signal, Engine Temperature Signal & Interior Temperature Sensor Fan

1998 Audi A4 Avant Quattro, AutomaticSECTION A/C Pressure Switch, A/C Compressor Signal, Engine Temperature Signal & Interior Temperature Sensor Fan
WARNING: This page is about a different car, the 2001 Audi S4, 2001 Audi A4, 2000 Audi S4, and 2000 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
  1. Use Adapter Cable (VAG 1598/11). Connect LED Voltage Tester (VAG 1527B) between adapter cable terminals No. 12 and 14. Start engine and ensure A/C compressor is OFF. LED should illuminate. If LED does not illuminate, check for open or short circuit in wiring between A/C compressor and A/C-heater control panel. Repair or replace as necessary.
  2. Ensure LED voltage tester is still connected between adapter cable terminals No. 12 and 14. Start engine and ensure A/C compressor is ON. LED should illuminate slightly dimmer than in previous step. If LED does not illuminate as specified, check for A/C compressor switch-off conditions caused by ECM or TCM. See A/C COMPRESSOR SWITCH-OFF CONDITIONS (DISPLAY GROUP NO. 01)  table under SELF-DIAGNOSTICS. Check for short to ground in wiring between A/C compressor and A/C-heater control panel. Repair or replace as necessary.
  3. Connect LED voltage tester between ground and adapter cable terminal No. 51. Start engine and allow to idle. LED should illuminate. If LED does not illuminate, check for short to ground between A/C compressor and A/C-heater control panel. Check for A/C compressor switch-off conditions caused by instrument cluster. See A/C COMPRESSOR SWITCH-OFF CONDITIONS (DISPLAY GROUP NO. 01)  table under SELF-DIAGNOSTICS. Repair or replace as necessary.
  4. Set DVOM to 200-milliamp scale. Connect test leads between ground and adapter cable terminal No. 12. Start engine and allow to idle. With A/C compressor off, less than 5 milliamps should be present. If more than 5 milliamps are present, repair short to voltage.
  5. With A/C compressor on, less than 50 milliamps should be present (compressor not engaged). If greater than 50 milliamps are present, replace A/C-heater control panel.
  6. Remove test leads from adapter cable. Ensure A/C compressor engages. If A/C compressor does not engage, check for A/C compressor switch-off conditions caused by ECM or TCM. See A/C COMPRESSOR SWITCH-OFF CONDITIONS (DISPLAY GROUP NO. 01)  table under SELF-DIAGNOSTICS. Check for short to ground in wiring between A/C compressor and A/C-heater control panel. Repair or replace as necessary.
  7. Set DVOM to 200-ohm scale. Turn ignition off. Connect DVOM test leads between adapter cable terminals No. 2 and 42 or backprobe A/C pressure switch terminals No. 1 (Brown/Blue wire) and No. 2 (Brown/White wire). Resistance should be less than 20 ohms. If resistance is not as specified, check for open circuit or high resistance in A/C pressure switch circuit. Check A/C pressure switch. See A/C PRESSURE SWITCH  . Repair or replace as necessary.
NOTE: If A/C compressor cut-off condition code 1 (A/C pressure switch open) appears in measuring value block, display group 1, field 1, check for intermittent contact connections in wiring harness. Also check cooling fan low speed and A/C pressure switch functions. If no fault can be determined, check A/C system pressures.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

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