Repair Manual MAN-00
190
THAR
CRDe
BS-IV
MAY
2012
/Rev 1
The repair methods given by the manufacturer in this document are based on the technical specifications, current at the time of release. The methods may be modified as a result of changes introduced by the
manufacturer in the production of the various component units and accessories from which the vehicles are manufactured. The reproduction, translation, transmission, in part of or whole of the present
document, are prohibited without the prior written consent of Mahindra & Mahindra Ltd. The use of this document by any person other than the trained personnel, at the Authorized Service Centre of
Mahindra & Mahindra Ltd., will amount to unauthorized use and shall be liable for penalty/prosecution© 2012 Mahindra & Mahindra Ltd.
To engage and disengage the fan drive the bi metal coil senses the air temperature behind the
radiator. When a pre determined temperature is reached, the coil opens a valve, which allows the
fluid to enter the drive area and due to centrifugal forces circulate to the annular drive area
There are two sets of annular grooves. , One in the drive clutch and the other in the drive body, a
specific clearance being provided between two sets of grooves. When this clearance is filled with
viscous fluid a shearing action caused by the speed differential between the two drive components,
transmit the torque to the fan. The fluid is thrown to the outside of the unit by the centrifugal force
from where it is recirculated to the reservoir via the pump plate adjacent to the drive member.
If the engine sped is increased the amount of slip will also increase to limit the maximum fan speed.
When the air temperature from the radiator drops sufficiently, the bi metal coil closes the valve and
prevents fluid entering the drive area. The fluid that is in the drive area will gradually pump out into
the reservoir and the fan will return to an idle condition
Checking the VFD –
This procedure will only give an indication that the fan is cutting in and out, but will not be able to
check the accuracy of the cut in temperature.
Depending on the level of the test equipment there are several ways to check the if the fan is working
correctly.
Using a non-contact tachometer –
1.
Run the engine at idle without any load for approximately 3 minutes, for example at 2000 rpm,
observer the fan drive speed. In the disengaged mode the fan speed will be approximately 800
rpm. By running for 3 minutes it will ensure that the fan drive has pumped out the silicone fluid
into the reservoir and that the fan drive will be in the cut out ( idle)
2.
Either
(a)
Blank the radiator by using a sheet of cardboard, which has a 15-cm hole, cut out of in line
with the center of the fan drive. This will allow a flow of air on the bimetal coil and the
cardboard will allow the radiator to heat up quickly.
Keep a check on the vehicle temperature gauge and let the water temperature rise to about
105
°
C. this will ensure that the fan drive will engage
(b)
Using a commercial hot air blower, which will provide a hot air flow of at least 75
°
C, direct the
air on to the centers of the fan drive through the radiator. Keep the hot air on for several minutes.
This will cut the fan drive in, and the fan speed will increase. It is important that only a powerful
blower is used so that the hot air should reach the fan drive after going the radiator at the correct
temperature.
3.
Once the fan drive has become engaged by either method (a) or (b). Check the fan speed with the
non-contact tachometer. At 2000 rpm input speed the fan speed should be 1800 rpm.
Testing without a non-contact tachometer –
4.
Use the same method explained in step 2, but this time listen to the noise level generated by the
fan. With the fan in the idle condition the noise level should be very low, however when the fan
speed increases in the engaged mode there will be a significant roar from the fan. This will clearly
indicate if the fan drive is working.
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