Fault Code Guide

A/C Clutch Circuit Tests for Diagnosing No A/C Clutch Engagement
Test Conditions Test Point/Method
Good
Result
What to Do if Test Fails
A/C request
input
key on, engine on
air selection switch in one of A/C
settings
fan (blower) speed on any
setting but off
connect ServiceLink and use the
"A/C Clutch Function" Datalink
Monitor template to see if the
A/C request is seen by the BHM
ServiceLink/Datalink Monitor
NOTE: Make sure the
Datalink Monitor template is
not in Test Mode. The
control head should request
A/C. This will cause the "A/C
Request" annunciator on the
template to indicate that the
request is on. If the
annunciator does not
indicate that a request for
A/C is received, check the
settings on the control head
before proceeding with
"What to Do if Test Fails."
A/C
request
is
received
by the
BHM
Perform the "Evaporator
Probe Circuit Tests."
Check wiring between the
control head and the bulkhead
module. Check for an open
circuit.
Check the control head.
Check the bulkhead module.
Try to manually ground the
A/C request input while
observing the template to
confirm.
A/C clutch
circuit
*
key on, engine off
connect ServiceLink and use the
"A/C Clutch Function" Datalink
Monitor template to manually
actuate the A/C clutch output
ServiceLink/Datalink Monitor
NOTE: Put the template in
"Test Mode" and actuate the
A/C clutch by selecting the
button for "Clutch On." You
should hear a distinct click
when the clutch engages.
The A/C clutch annunciator
(BHM to clutch) should turn
on when the output is
energized. If this annunciator
indicates that the output is
on but the clutch does not
engage, then the problem is
in the A/C clutch circuit and
not with the BHM. If the A/C
clutch annunciator does not
indicate that the output is
energized when the output is
turned on and the clutch
does not engage, then the
problem is with the BHM.
A/C
clutch
should
engage
Check continuity across the
binary switch. If the circuit is
open, check if the refrigerant
pressure is within operating
range of the binary switch.
(Refrigerant pressure may be
very low or too high.) If
pressures are okay, replace
binary switch.
Check for faulty wiring.
Check for faulty A/C clutch
ground circuit.
Check for faulty A/C clutch
coil (coil resistance should be
3Ω ±0.5Ω).
Check for faulty BHM (see
note in Test Point/Method
column).
*
Circuit faults with the A/C clutch output may generate bulkhead module fault codes.
Table 10, A/C Clutch Circuit Tests for Diagnosing No A/C Clutch Engagement
Backlighting Circuit Tests
Test Conditions Test Point
Good
Result
What to Do if Test Fails
backlighting
circuit ground
test
battery switch on (if equipped)
key off, engine off
control head connector
disconnected
Measure between pin B8 of
the control head connector
and the positive battery post.
12V
*
Check for an open in the
control head ground circuit.
Cab Heater and Air Conditioner, Valeo 83.00
Troubleshooting
Business Class M2 Workshop Manual, Supplement 13, March 2008 300/17