The condenser fan on my Bosch frig stopped so I bought a new one, original Bosch part D4612AAA22, 13v, 2.5W 1100rpm, 0.178A. (too weak IMHO). Now the new fan struggles to get going, like the current isn’t enough to overcome the required startup torque. With no blade fitted the motor will cycle on and off ok, but with the blade fitted it needs a flick of the finger to get going. The motor spins well (when it get going) and the blade is really light and well balanced, and the power supply is a stable 13.2V. Is there any way to fit a capacitor or something to give it a boost on startup?? Any advice greatly appreciated.

 

The very first thing to check is the supply voltage when the fan does not want to start spinning. Is it actually the 13 volts? Then the second thing to check would be the fan friction. I am guessing that it s a brushless DC motor, so worn brushes would not be the problem.
So the next suspect is friction in the bearings and rotating effort. Give the blade a spin, with power off. It should coast a bit. If not, excessive friction is present.

 

Bearing failure.

 

The supply is stable at 13.2v. Motor is a new DC brushless type and it spins freely. this is kinda perplexing because the engineering and quality is there so you wouldn't expect such a simple thing to be a problem. When the compressor/fan cycle starts you can literally flick it with a feather and it goes. Maybe I'll run it on the bench for a few days to bed it in.
Who builds a 2.5watt motor anyway!
Can't beat horsepower.

 

Now there is a chance that there is the same reason the replacement fan is not working as for why the previous fan was not working. What checking did you do on the fan motor that was replaced? Was there a similar problem , or was it a total failure? If you still have the failed fan, it could be that both will run quite well on a higher voltage.
It may be that the fans are actually built to run on a higher voltage. It would not be the first time that a released product design was not quite right. Keep in mind that in many consumer market products, reliability, and quality in general, rank far behind profit as design targets.. The primary corporate responsibility is to the shareholders, the customers are not even on the list of those to be satisfied.