Fault Code Guide

Evaporator Probe Circuit Tests
Test Conditions Test Point
Good
Result
What to Do if Test Fails
evaporator
temperature
probe
key off, engine off
sensor probe removed and
disconnected
fill a cup with ice then add water
to make an ice-water bath
NOTE: use mostly ice and allow
time for temperature to stabilize
at 32°F (0°C)
place the tip of the evaporator
probe in the ice-water bath for 5
minutes before testing—leave
the tip immersed while taking
the resistance
measurement—be sure the
meter reading is stable before
noting the final measurement
Measure across pins on the
temperature probe.
for pre-
1-8-07:
16,000
to
16,730Ω
at 32°F
(0°C)
—
for
1-8-07
on:
8910 to
9090Ω
at 32°F
(0°C)
Replace temperature probe.
evaporator
temperature
probe circuit
test
battery switch on (if equipped)
key on, engine off
sensor probe installed, but
connector is disconnected
Measure across temperature
probe connector terminals.
5V Check for an open in circuits
338K and 338GP.
If wiring is okay, replace the
control head.
Table 9, Evaporator Probe Circuit Tests
A/C Clutch Circuit Tests for
Diagnosing No A/C Clutch
Engagement
The A/C compressor clutch is controlled by the con-
trol head (climate control panel). When the control
head determines that the A/C compressor is re-
quired, it grounds the A/C request input to the bulk-
head module (BHM). When the BHM receives the
A/C request signal from the climate control panel, it
will apply power to the A/C clutch output when the
following conditions are met—
• engine has been running more than 5 seconds;
• battery voltage is greater than 9.25V;
• low air pressure warning is not active on the
ICU;
• A/C clutch has not been engaged in the previ-
ous 15 seconds.
NOTE: The A/C clutch cycle timer strategy is
implemented differently, depending on BHM
software versions. With BHM software version
6.1, the total A/C clutch cycle time (on + off
time) is a minimum of 15 seconds. This ensures
that the A/C compressor does not cycle more
than 4 times per minute. With BHM software
versions 6.4 and 6.5, the minimum compressor
off time is 15 seconds. This means the total
cycle time (on + off time) will always exceed 15
seconds. This too, ensures that the A/C com-
pressor does not cycle more than 4 times per
minute.
The BHM sends power to energize the A/C clutch. A
binary switch is wired into this circuit, which will pre-
vent the compressor clutch from engaging if the re-
frigerant pressure is too high or too low.
When all of the following conditions are met, the
control head will send the A/C request signal to the
bulkhead module:
• The air selection switch is in one of the A/C or
defrost settings, or the recirculation mode is
on.
Cab Heater and Air Conditioner, Valeo 83.00
Troubleshooting
Business Class M2 Workshop Manual, Supplement 13, March 2008 300/15