Hi, could you help me if you can, please?

I have a Focus MK1 and blower fan started to do a weird thing. It starts but after a short time it just start to become slow then stops. We tried to find the root of the problem so we connected the fan to another car's battery (directly, without any switch) and the fan started, slowed down and finally stoped. What could I change? The whole fan part?

Many thanks in advance.