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CLIMATE CONTROL
Fault finding – Help62B
V3 MR-372-J84-62B000$120.mif
Vdiag No.: 44
CLIMATE CONTROL
Fault finding – Help
MEASURING THE CONTROL VOLTAGE OF THE PASSENGER COMPARTMENT BLOWER
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 voltage measurement):
With the power module connector connected, measure across track 6 of the module and the earth.
At speed 0 the voltage measured is equal to the battery voltage (± 1 V) and at speed 8 the voltage is 5 V (± 0.5 V). The
voltage varies between 0 and 14 V for the seven intermediate speeds.
Examples of measurements taken with the voltmeter with the engine at idling speed (values given as a guide):
2 / MEASURING USING
AN OSCILLOSCOPE (Optima 5800, CLIP technique):
The blower 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 (5 V).
To take the measurement, connect the earth lead of the oscilloscope to the battery earth and the measuring lead of the
oscilloscope to track 6 (6-track connector) of the power module (module connector connected).
Adjust the time base on the oscilloscope to 500 µµ µ µ
s per division with a calibration of 5 V per division.
The signals obtained should be: a straight line at 14 V (± 1 V) for speed 0, and a straight line at 5 V (± 0.5 V) for speed 8.
Examples of measurements taken with the oscilloscope with the engine at idling speed (for information only):
* Passenger compartment blower PWM: passenger compartment blower pulse width modulation control voltage.
Passenger
compartment
blower speed012345678
Voltage
measurement13.77 V 12.26 V 11.79 V 11.22 V 10.43 V 9.44 V 8.08 V 6.66 V 4.96 V
PR019
Passenger
compartment
blower PWM
setting*0% 18% 23% 30% 39% 51% 66% 82% 100%
Passenger
compartment
blower speed012345678
Duration of high
status....... 450 µs400 µs350 µs300 µs250 µs200 µs150 µs.......
Duration of low
status....... 50 µs100 µs150 µs200 µs250 µs300 µs350 µs.......
PR019
Passenger
compartment
blower PWM
setting*0% 18% 23% 30% 39% 51% 66% 82% 100%
ACREG X84 1.1
Edition 2
MR-372-J84-62B000$120.mif
