Okay everyone I'm back. Sorry for the time delay. Im finishing a masters degree and I had to complete some laboratory work during the last weeks.

Concerning the compatibility of the transistors, I personnaly checked the power rating, the saturation resistance and the maximum cutoff voltage

If the power rating is too low, the mosfet will heat too much and will fail prematurely.

If the resistance is higher than the one specified on the original transistor spec sheet, the maximum fan speed will be reduced.

If the cutoff voltage is too low, the inducting effect of the blower motor can overstress the semiconducting material by applying excessive voltage to the terminals when the transistor cuts off. This can lead to premature failure.

You can make your fan run full speed by shorting the two terminals of the big connector connecting the fan motor to the power stage. Be sure to use a big wire to short the connector since the current consumed by the blower motor at full speed is pretty high. Make sure that the wire doesnt heat up too much.

Using the 220 form factor, the only thing you have to do is solder wires from the transistor terminals to the circuit board connections. This is necessary because the to220 legs arent long enough to connect correctly to the pcb. Again, the wires you use to lenghten the drain and emitter pins should be at least the same size than the pin itself.

ps.: My repair is still working well!