Heater went off last week and doing a fair bit of research on here there was not a great deal of information on where to look for sorting the problem out .... so if your heater goes off and setting 4 is the only one working then heres how you solve it..
1 remove the glove box using a philips screw driver of the right size.3 screws.
2 remove the 4 scrivits that hold the cardboard coverd carpet thing in place.. turning them round and round with a philips screw driver till they decide to come apart... 3 on the section under the glove box and 1 on the heater motor.
3 lying on your right side and looking at the heater motor above the heater you will see whats left of something melted that has 4 thick wires going into it to the right of that there is a philips screw remove that screw. now you can with a flat screw driver break the melted plastic and remove your resistor.
4 now is the awkward part with a stanley knife remove the melted plastic sufficiently to alllow the replacement resistor to be fitted... this is done by removing a bit then trying the new one in then removing a bit more if needed.
5 replacing everything back again is the reversal of the above information...
you will not find any of this in a haynes manual as they are getting worse.. they used to do a proper job of giving the average DIYer a good bit of information.. the information they give these days is with everything else removed to give a clear picture of what you have to remove.. but when you look at the picture you think this going to be easy then you look at the vehicle thats when it hits you there is an awful lot of other things in the way...
Job time around 15 minutes if you have all the tools to hand.. as well as the replacement resistor... Easy peasy