No, a 140 is super easy to get to the blower, it's under the air intake cowl behind the engine, but not in the center like I think Sixto is thinking, it's over on the passenger side. There are about 6 large phillips screws holding the panel down and you're "there".
Do a search, the *usual* problem is the blower motor regulator, it's held down to the blower motor by 2 screws, but it's real pricey, surprisingly pricey for such a small part.
I've also seen this problem caused by a faulty ignition switch on a 140. For the price of the parts involved (motors, regulators, ignition switches) it would pay to have an experience 140 mechanic look it over. By my estimation though "8 times out of 10" it's the regulator, but I'd still want to test it. At least uncover the motor, disconnect the regulator, and give the fan motor 12 volts and see if the motor at least is capable of working, then you know it's not the motor, it's either the regulator or something "upstream" of the regulator. MB has published a test procedure specifically for this problem, I don't have it though, not here. Stevebfl or Dr Diesel probably does, doesn't seem like it was all that involved.