Picked up a 2012 ducato maxi there is hot air coming from vents but no blowers 1-4 doesn’t work checked the heater resistor terminal 5 blown and the male connector. Replaced both and still nothing checked the F08 fuse in the engine bay seemed ok so replaced it anyway checked for the heater relay in the engine bay swapped it with another relay and still nothing so can it be the controller with the resistor behind it that’s gone help if there is already a thread someone please send me to it

There should be 12v at the heater blower positive terminal at all times the ignition is ON via a fuse and relay in the engine fusebox. The negative connects to the motor via the fan switch and resistor pack. On position 4 the resistor pack is bypassed and negative is fed directly to the motor via the switch.

So if the switch ie on the back of the controls is broken the blowers won’t work at all ?

That is correct. The drawing shows that the switch must work to feed negative directly to the motor on switch position 4 or via resistor combinations on switch position 1 to 3.
It should be relatively easy to use a test lead connected to negative to bypass the switch to prove the motor, including the positive supply to it, is ok.