Thank you for your question, my name is Steve and I am a fully qualified vehicle technician with over thirty years in the trade, hopefully I can help.
Starting with the windows these may simply need resetting, to do this, Switch the ignition ON.
Then Lift and hold the window switch to fully close window, Release the switch. Then Lift and hold the window switch for 1 second.
Next Press and hold window switch to fully open window. Release switch. Lift and hold window switch to fully close window. The window should not operate automatically as before, you will have to repeat this procedure for all windows. Then Switch ignition off.
The heater fan is as you say probably the resister pack, on your Fiesta this can be found up under the passengers side footwell to the side of the heater box, behind a small trim panel, once the panel is removed you should be able to see it ok. I have attached a picture from the manual.
I hope this answers your question but do please feel free to ask any further questions by replying to this thread.
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