Heater not working

[Juddy]

Hi all, probably had this question a few times so i will apologise in advance. My 55 plate 2.0 16v heater isn't working so after doing a little research i concluded it must be the resister pack, anyhow after unplugging the wiring at the fan unit and tested for voltage I'm getting 14v there on all 4 settings. Now this is obviously pointing towards the fan unit itself. Now my question is what kind of job is it to take out and change also does the fan have to be from an identical car ( 2.0 16v ) or are they all the same as long as it's from a mk 2?
Thanks.