A8 Quattro Sedan V8-4.2L (ABZ) (1998)
A/C Signal: Testing and Inspection
Air conditioning signals, checking
NOTE: When A/C is switched on, Engine Control Module (ECM) terminal C14 receives a positive (+) voltage signal.
Test conditions
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Vehicle at room temperature, greater than 15 °C (59 °F)
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No A/C malfunctions stored in DTC memory
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Engine Coolant Temperature (ECT) at least 85 °C (185 °F)
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ECM coding OK
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Transmission selector lever in Neutral position
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Rear window defogger switched off
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Connect VAG1551 or VAG1552 Scan Tool (ST) and press buttons -0- and -1- to insert "Engine Electronics" address word 01 (engine running at
idle). Refer to "Scan Tool Testing/Scan Tool Connecting and Initial Checks/VAG1551 or VAG1552 Scan Tool" See: Testing and Inspection
Indicated on display
Rapid data transfer
HELP
Select function XX
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Press buttons -0- and -8- to select "Read Measuring Value Block" function 08, and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block
Input display group number XXX
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Press buttons -0-, -2- and -1- to input display group number 21 (021), and press -Q- button to confirm input.
Indicated on display
Read Measuring Value Block 21
->
1
2
3
4
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Check specified values for A/C operating conditions (display fields 2 and 3):
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Switch A/C on; press "Auto" button; set "-" or "+" buttons for maximum heating, or maximum cooling, as specified.
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Specified value in display field 2: A/C-High
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Specified value in display field 3: Compr-on
If specified values are not displayed:
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Stop engine (switch ignition off).
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Connect VAG1598/19 test box to ECM harness connector. Refer "Scan Tool Testing/SCan Tool Connecting and Initial Checks/VAG1598/19
Test Box, Connecting" See: Testing and Inspection
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Connect VAG1527B LED voltage tester between ECM/test box sockets C14 and D11 (Ground).
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Switch ignition on.
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Switch A/C on.
LED must light up.