Fault Code Guide

• The fan switch is on any setting other than off.
• The evaporation sensor temperature is above
40.1°F (4.5°C).
When these conditions exist, the control head sends
the A/C request signal to the bulkhead module. See
Fig. 2.
NOTE: The A/C signal will remain active until
the evaporator sensor reaches 38.3°F (3.5°C),
the fan is turned off, or the air selection switch
is taken out of defrost or A/C mode.
See Table 10 for the A/C clutch circuit tests. Perform
the tests in Table 10 in the sequence presented. The
directions under the column "What to Do if Test
Fails" are sometimes dependent on good results
from previous tests. If any of the tests fail, stop and
perform the specified repair or check.
NOTE: If these tests pass and the A/C clutch
still will not engage, check the following—
• make sure that the air system does not have
an active low air pressure warning;
• make sure that the battery voltage to all BHM
inputs is above 9.25V;
• make sure that the engine speed is available
(make sure it registers on the tachometer).
Backlighting Circuit Tests
See Table 11 for the backlighting circuit tests. Per-
form the tests in Table 11 in the sequence pre-
sented. The directions under the column "What to Do
if Test Fails" are sometimes dependent on good re-
sults from previous tests. If any of the tests fail, stop
and perform the specified repair or check. If all of the
tests pass and the backlighting at the control head
still does not operate properly, check the control
head.
Fault Codes
If the A/C clutch is not working, use ServiceLink to
check for fault codes. See Table 12 and Table 13 for
a description of the fault codes.
08/01/2006
f543963
A/C Relay Control
Control panel grounds A/C
request to BHM when control
rules are met.
A/C Clutch
A/C Request
Control Head (climate control panel)
Bulkhead Module (BHM) Binary Pressure Switch
HI
LO
A/C Clutch
+12V
High Cut Out 427 to 484 psi
(2944 to 3337 kPa)
High Cut In 313 to 427 psi
(2158 to 2944 kPa)
Low Cut Out 27 to 35 psi
(186 to 241 kPa)
Low Cut In 28 to 36 psi
(193 to 248 kPa)
BHM sends 12V through the binary switch
to the A/C clutch when it receives the A/C
request from the control head and the
following conditions are met:
−Engine has been running more than
5 seconds.
−Battery voltage is greater than 9.25V.
−Low air pressure status is not active
(not low air).
−A/C clutch countdown timer conditions
have been met.*
*
See A/C clutch cycle timer strategy note above.
NOTE: Binary pressure switch positions indicate little or no system pressure.
Fig. 2, A/C Clutch Control Circuit
Cab Heater and Air Conditioner, Valeo 83.00
Troubleshooting
Business Class M2 Workshop Manual, Supplement 13, March 2008300/16