Disco 1 Blower blowing nicely just on one side

Hi! I have a Disco 200TDI from 1992 and when I turn the blower on I hear the air blowing pretty strong somewhere on the right side of the car but there is little or no noise on the left side. And on the right side the air is blowing pretty nicely whereas on the left side almost no air is coming out. What can be the reason? Do I need to take everything out or is there something I can try before disassembling everything? This is a version with air conditioning, same symptoms apply both to air con and heating.