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HOMESERVICE MANUALSAUDI1996A4 BASE, STANDARDREPAIR AND DIAGNOSISHEATING, VENTILATION & A/C (HVAC)HVAC CONTROL SYSTEMSA/C-HEATER SYSTEM - AUTOMATICTESTINGA/C COMPRESSOR SPEED SENSOR, PRESSURE SWITCHES & INTERIOR TEMPERATURE SENSOR FAN
1996 Audi A4 Base, Standard

A/C Compressor Speed Sensor, Pressure Switches & Interior Temperature Sensor Fan

1996 Audi A4 Base, StandardSECTION A/C Compressor Speed Sensor, Pressure Switches & Interior Temperature Sensor Fan
NOTE: Steps 1-3 do not apply to vehicles equipped with Nippondenso compressors.
  1. Put DVOM in 20,000-ohm range. Using Adapter Cable (VAG 1598/11), use DVOM to check resistance between Test Box (VAG 1598) terminals No. 5 and 49. If resistance is not 800-1500 ohms, check for short, open or high resistance in Gray/Green or Brown/White wire between A/C compressor speed sensor, A/C-heater control panel, and ground. Check A/C compressor speed sensor. Repair or replace as necessary.
  2. Check resistance between test box terminal No. 5 and ground. If resistance is not greater than 2000 ohms, check for short circuit in Gray/Green or Brown/White wire between A/C compressor speed sensor, A/C-heater control panel, and ground. Check A/C compressor speed sensor. Repair or replace as necessary.
  3. Put DVOM in 20-volt range. Check voltage between test box terminal No. 5 and ground. Start engine. Ensure A/C compressor is not running. If reading is not less than one volt, repair short in Gray/Green or Brown/White wire between A/C compressor speed sensor, A/C-heater control panel, and ground.
  4. Put DVOM in 2-volt range. Check voltage between test box terminal No. 5 and ground. Start engine. Turn A/C compressor on. RemoveA/C clutch relay. Connect jumper wire between Black/Red and Green/Yellow wires at A/C clutch relay harness connectors (A/C clutch should be switched on). If reading is not greater than 0.05 volt (depending on engine speed), replace A/C compressor speed sensor.
  5. Put DVOM in 200-ohm range. Check resistance between test box terminals No. 2 and 49. If resistance is not less than 20 ohms, check for poor connection, open or high resistance in Brown/Blue or Brown/White wire between high pressure cut-out switch, A/C-heater control panel and ground. Check high pressure cut-out switch. Repair or replace as necessary.
  6. Put DVOM in 20-volt range. Check voltage between test box terminal No. 3 and ground. Turn ignition on. If about battery voltage does not exist, check for open in Gray, Black, or Black/Blue wire between low pressure switch, A/C-heater control panel and ground. Check low pressure switch. Check A/C system pressures. Repair or replace as necessary.
  7. Put DVOM in 20-amp range. Check amperage between test box terminal No. 44 and ground. Turn ignition on. If reading is not less than one amp or interior temperature sensor fan does not run, check for open or short in Brown wire between interior temperature sensor fan and A/C-heater control panel. Repair as necessary.
  8. Connect LED Tester (US 1115) between test box terminals No. 12 and 13. Start engine. If LED in tester comes on, check for short in circuits between A/C compressor, A/C-heater control panel, and ground. See WIRING DIAGRAMS  . Check for A/C compressor switch-off conditions caused by ECM or TCM. See A/C COMPRESSOR SWITCH-OFF CONDITIONS  under SELF-DIAGNOSTICS. Repair or replace as necessary.
  9. Connect LED tester between test box terminals No. 13 and 51. Start engine. If LED in tester comes on, check for short in circuits between A/C compressor, A/C-heater control panel, and ground. See WIRING DIAGRAMS  . Check for A/C compressor switch-off conditions caused by instrument cluster. See A/C COMPRESSOR SWITCH-OFF CONDITIONS  under SELF-DIAGNOSTICS. Repair or replace as necessary.
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.