Does anyone know the location of the resistor pack?
I'm not getting very good temp control on the dial. As soon as I click it off Lo..the air gets hot

There's a useful pdf in the Electrics section (Whattodowhenyourheaterfanstopsworking) here:

https://sites.google.com/site/fiatmultipla/Home/repairs

Lankytim may have some sage words too. He's lurking on here with his sick injectors atm and I know he had problems with his heater fan a while ago.

The resistor pack will affect fan speed, not air temperature.

If you have climate control, then this may be due to Fiat's (or rather Magneti Marelli's) 'winter warm-up' algorithm. This algorithm thinks that if the temperature control is not set to Lo, then you want warm air for 1/2 an hour, to get the cabin temperature up.
Check whether the temperature control starts working correctly after 1/2 an hour, if you have a longer trip planned.
This happens on mine too (- always has). I don't know if there is an associated temperature sensor fault, but it does seem to work correctly after 1/2 an hour.

Only thinking that as someone had a similar problem on fiat coupe forum..and that uses an identical heater control panel as the multi!

Think I've sorted it..after reading a something similar with a different fiat.
There is a small fan behind the grill on the heater control panel that gets clogged and stops spinning..causing the graduation from hot to cold on the dial stop.
So I took it apart and low and behold its was full of gunk..cleaned it out and then plugged in and the fan spun on nice and freely..
All back together and it all seems fine now..can now have warm air instead of just hot or cold!!

Good to hear you got it sorted. How do you get at this fan?

Once you take the heater panel off its held to the air con and recirculating switches..so you have to remove them first.. Only held by 4 or 5 screws..then it reveal s the 2 screws holding the fan assembly..and here you will find the 13 years worth of skin, hair and bogeys!!