Fault Code Guide

Blower Motor Circuit Tests
Test Conditions Test Point
Good
Result
What to Do if Test Fails
blower motor
ground circuit
battery switch on (if equipped)
key off
blower motor connector removed
Measure between pin 3 of
blower motor connector and
the positive battery post.
12V
*
Check for an open in blower
motor ground circuit.
PWM signal
from control
head
battery switch on (if equipped)
key on, engine off
blower motor connector
disconnected
change the fan (blower) speed
setting on the control head and
observe frequency using the
digital multimeter (DMM)
Probe pins 4 and 5 of the
blower motor connector,
harness side (DMM set to
measure frequency).
0Hz
fan off
0Hz
fan on
high
2000
Hz all
other
speeds
Check circuit 338H.
Check control head.
voltage drop
(power circuit)
battery switch on (if equipped)
key on, engine off
all connectors connected
fan (blower) speed on high
Backprobe pin 4 at the
blower motor connector,
other lead on positive battery
post.
less
than
0.5V
Locate high resistance or
open in circuit 98F.
voltage drop
(ground circuit)
battery switch on (if equipped)
key on, engine off
all connectors connected
fan (blower) speed on high
Backprobe pin 3 at the
blower motor connector,
other lead on negative
battery post.
less
than
0.5V
Locate high resistance or
open in blower motor ground
circuit.
blower motor
current draw
battery switch on (if equipped)
key on, engine off
all connectors connected
fan (blower) speed on high
Use current clamp around
circuit 98F or blower motor
ground wire.
less
than
23.5A
Check blower motor.
*
The voltage should be approximately the same as the battery voltage.
Table 6, Blower Motor Circuit Tests
Evaporator Probe Circuit Tests
The evaporator temperature sensor is a resistive ele-
ment, where the resistance increases as the tem-
perature decreases. The control head (climate con-
trol panel) uses this sensor to determine the
evaporator temperature. The control head uses the
temperature information to determine if the A/C com-
pressor should be engaged or not in order to prevent
the evaporator core from freezing. As refrigerant
flows through the evaporator, condensation will form
on the surface of the evaporator. If this condensation
freezes because the evaporator temperature is too
low, airflow will be restricted through the core and
poor cooling will result. The control head will shut off
the compressor when the evaporator temperature is
near the point where freezing may occur. See
Table 7 for evaporator probe temperature versus re-
sistance values for units manufactured up to and in-
cluding January 7, 2007. See Table 8 for evaporator
probe temperature versus resistance values for units
manufactured on or after January 8, 2007.
Perform the tests in Table 9 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.
Cab Heater and Air Conditioner, Valeo 83.00
Troubleshooting
Business Class M2 Workshop Manual, Supplement 13, March 2008 300/13