The air from the vents is cold but the blower is so feeble that there is no effective cooling. Would someone suggest what could be done.

As always, thank you for your advice.

Best wishes,
khemanthkumar

Your problem may be caused by dirty components. First, look for the air sampler blower. A clue would be a small air intake like a vent. I am not familiar with this chassis as much as the W126 but your 'vent' may be in the over head light fixture.
The W126 sample blower is located under the glovebox and the W201 is behind and under the passenger vent. Yours could be here too. But looking online at a new sampler, the design appears to be in the light fixture.
The sample blower takes air from the cabin and blows it over a temp sensor. If this temp sensor is dirty, it can not send a signal as effectively to the blower regulator to increase or decrease the blower speed.
This would be the easiest test.
If the blower speed does not change after this test, remove the blower itself. Again from looking at a new blower design, your blower is under the glovebox behind the knee bolster.
Pics attached are the componants to look for. Pic of blower regulator was not available.
The next problem area to check is the spin of the blower cage. And cleaning the dirt out.
Check for free spin by manually turning the cage. Spin should have little resistance. If you have a battery charger, use it as a 12V source to connect the blower directly. Does it spin full speed that way? Check brush wear. Two brushes shaped like small rectangles. One on each side of the armature and each having a copper wire attached like an umbilical cord.
If the blower spins full speed with direct power, and the brushes look good, then the next area to check would be the blower regulator.
Not sure on testing this part.

Attached Thumbnails

   

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Usually a blower regulator issue. Should be many posts in archives under blower regulator.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician