Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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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
1998 Audi A4 Avant Quattro, Automatic
A/C Pressure Switch
1998 Audi A4 Avant Quattro, AutomaticSECTION A/C Pressure Switch
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.
NOTE:
A/C pressure switch contains 2 switching elements. Compressor is shut off due to low or excess refrigerant system pressure (switch open at terminals No. 1 and 2). Second stage (speed) coolant fan is switched on (switch closed at terminals No. 3 and 4).
- Start engine and allow to idle. Turn A/C on, using AUTO operating mode on A/C control panel. Connect A/C gauge set and monitor A/C system pressures. Disconnect A/C pressure switch harness connector.
- Compressor should disengage, simulating an open low pressure switch. Remove A/C pressure switch and reconnect harness connector. Compressor should remain disengaged simulating an open low pressure switch. If compressor does not engage, go to next step. If compressor does not disengage, repair short circuit.
- Disconnect pressure switch harness connector. Using a fused jumper wire, connect pressure switch harness connector terminals No. 1 (Brown/Blue wire) and No. 2 (Brown/White wire). See Fig 1 . Compressor should engage.
- If compressor engages, check for low refrigerant pressure or empty system. If refrigerant pressures are okay, check A/C pressure switch. Replace switch as necessary. If switch is okay, repair open in wiring between switch and control panel.
CAUTION:
Using A/C gauge set, monitor system pressures. If system pressure becomes excessive, disconnect fused jumper wire and ensure compressor disengages.
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When to See a Mechanic
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.