Hi Beth,
I have an 07 Grande Punto and have had fun and games with the heater fan for years – and had never had a problem with those of other (non Fiat) cars I’ve owned. I don't know whether your car is similar in its electrical design/equipment to mine, but my problems - and their resolution - might help you solve yours.
1)
Resistor block failure
My fan's 4 speed switch governs fan speed via a ceramic-encased block of in-line resistors that looks like a pale green ice lolly without a stick. This weird thing is mounted in one of the plastic airways leading to the fan – presumably so that incoming air keeps it cool. On my car it’s under the dashboard on the passenger side, and you need to be a limbo dancer to get to it. Find a multi-plug with six or so cables entering it and you’ve got it. The block’s held in place by a single, tiny screw – male hex head, I think, about 5mm/5.5mm AF.
At position 4 these resistors are bypassed (i.e. there’s no resistor, in effect), so the fan gets 12V (or whatever the alternator is putting out). (Have a look at the circuit diagram someone posted and you’ll see what I mean.) At positions 1, 2 & 3 the relevant resistor drops the voltage, and hence the fan speed. Manipulating voltage in such a way (presumably) causes the resistors to heat up - so despite it being cooled by incoming air the resistor block doesn't last more than a few years. What tends to happen is that its coating spalls as one or more of the resistors breaks down. Since position 4 doesn’t have a resistor, if the fan works at that setting but not at one of the others, you know what the issue is. I gather some Punto owners just continue to run the fan at the highest speed. Works fine but it’s pretty noisy.
When my fan first stopped working a few years ago I discovered the block so badly burnt out that the path at position 4 had also perished. I replaced the block (£10-odd from Ebay) and the problem was solved. (Had to splice it into the existing wiring using a strip of heavy duty (30A) cable connector block - fiddly due to having to work upside down!)
2)
Fan running intermittently and unevenly, and at times not even coming on.
This happened twice last year, and each time it was the same issue. First port of call was of course the resistor block, but although it had started to crumble the fact that some power was getting though suggested that the fault might be with the fan itself.
It turned out to be carbon build-up on the fan rotor commutator – the usually shiny bobbin of copper that the two carbon brushes press against to magnetise the rotor windings. My guess is that it was caused by a combination of overnight condensation of damp air on the brushes/commutator and then running the fan for only a few minutes the following day (or the day after) on a short trip to the shops, etc.
Fan removal/repair procedure is/was as follows;
a) limber up for limbo dancing and find a torch
b) remove the twin cable multiplug from the fan body
c) remove the screw (female Torx head) securing the plastic fairing that directs hot air down into the footwell and tweak the fairing out (it’s fiddly to put back in)
d) remove the three tiny (5.5mm AF?) hex head screws securing the fan, and drop the fan out
e) remove the fan body cover to expose the commutator and brushes. (My cover was held in place by two tiny, rusty and very fragile looking male Torx headed screws which I was therefore loathe to touch – but while it’s visible with the cover on, cleaning the commutator of carbon deposits was soooo much easier with the cover off (and you can check brush life too). As it turned out the feeble Torx screws were into plastic, and loosened quite easily.)
f) hold a bit of emery cloth against the commutator, turn the fan several times by hand, and lo and behold, a nice clean contact surface once more. Blow out the arisings or they’ll shag your fan when you put it back together.
g) put it all back together and the fan should work again. Mine did.
h) visit a chiropractor to have them unravel your spine.
3)
Fan switched on but not coming on until you thump it or drive over a speed bump
I’ve had this happen too – and haven’t been able to find the cause. Checked all the cables, multiplugs, etc., but all seems well. That said, I’ve noticed that after cleaning the commutator this problem disappears for a while too, so I’m guessing it’s to do with carbon build up and that a quick jolt is enough to get the motor running each time, and that it then self-cleans (in a fashion).
***
Anyway, hope this helps you – and anybody else who has these niggling problems with Fiat heater fans. Last note: when I sourced the resistor block I seem to recall it fitting several models (and even makes) of car – so these faults and fixes may apply to other marques.
Happy New Year all,
Mick
). Once I’d replaced the resistor it still wouldn’t work, checked the pins and cables and all seem fine, no signs of wear or melting. If I gave the fan a bang it would attempt to go but just sounded like a bit of Card was stuck in it. 
