62B-96
MR-413-X44-62B000$966_eng.mif
V1
62B
CLIMATE CONTROL
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MEASURING THE CONTROL VOLTAGE OF THE PASSENGER COMPARTMENT FAN UNIT POWER MODULE
There are two ways to measure the control voltage of the passenger compartment blower power module:
1 / MEASURING USING A MULTIMETER (in the voltmeter position, direct current measurement):
This voltage measurement only gives an indication (average of non-representative voltages) and is not a rigourous
method. However, this method can be used if no oscilloscope is available or simply as a guide value.
With the power module connector disconnected, measure between connection 38LR of component 1023 and the
earth MAN.
At speed 0 the voltage measured is equal to the battery voltage (± 1 V) and at speed 8 the voltage is 0 V (± 0.5 V).
For the seven intermediate speeds, the voltage varies between 0 and the battery voltage.
Examples of measurements taken with the voltmeter with the engine at idle speed (values given as a guide):
Note:
These values are given for a battery voltage of + 12 V.
2 / MEASURING USING AN OSCILLOSCOPE (Optima 5800, CLIP technique):
The fan assembly power module is controlled by pulse width modulated control voltage (PWM*). This control voltage
is always 12 V, it is the control signal (square signal) that varies:
The amplitude and frequency do not vary but instead the high status (12 V) varies in relation to the low status (0 V).
To make this measurement, connect the oscilloscope earth lead to the battery earth and the oscilloscope measuring
lead to connection 38LR of component 1023 (power module connector connected).
Adjust the oscilloscope's time base to 500 µs per division with a range of 5 V per division and set the oscilloscope to
the Auto position by selecting the Trigger mode.
The signals obtained must be:
–a straight line at 12 V (±1) for speed 0,
–a straight line at 0 V (± 0.5 V) for speed 8. Passenger compartment
blower speed01 23 45 67 8
Voltage measurement
in V at the PWM* terminals11.73 V 9.5 V 9 V 8.3 V 7.2 V 6.6 V 5.4 V 3.6 V 0.4 V
Voltage measurement
in V at the fan assembly
terminals02.53.24.3 5.6 6.6 8 10 12
PR019 Passenger
compartment blower
PWM* setting0 % 20 % 25 % 33 % 43 % 50 % 60 % 77 % 100 %
Vdiag No.: 44
MR-413-X44-62B000$966_eng.mif
