A/C
Fault symptoms
The A/C compressor's clutch fails to engage.
Functions/Definitions
Information to the effect that the compressor is about to be engaged ("A/C IN") is
received via Motronic control module pin 64.
The control module prepares for this load increase by opening the idle air control valve
slightly.
Via pin 48 the Motronic control module then grounds the A/C relay which in its turn
controls the A/C compressor ("A/C OUT" or "A/C RELAY").
Basic requirement
No diagnostic trouble codes.
Diagnostic procedure
1. Check the A/C request ("A/C IN")
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Connect the ISAT Scan
Tool.
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Contact the Motronic
system.
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Activate the compressor from the
dashboard:
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The ISAT scan tool should read "ON".
Does the ISAT scan tool read "ON"?
Continue with point 2.
The fault is located before the Motronic (between the A/C button or ACC
control module and pin 12). Continue fault diagnosis as described in "Climate control system"
and Service Manual 3:2 "Electrical system, A/C-ACC".
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Note
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In the event of high engine coolant temperature or a fault in the coolant temperature
sensor signal sent to the ICE, the ICE will break the A/C
circuit.
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2. Check the A/C relay ("A/C OUT")
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Turn the ignition switch to the ON
position.
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Contact the Motronic
system.
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Both the A/C relay and the compressor clutch should now be
heard.
Conditions fulfilled?
No electrical fault present.
The fault is probably after the Motronic (i.e. between pin 48 and the
compressor). Continue fault diagnosis as described in "Climate control system"
. If no fault can be found, continue as described in
.
