Though this might be of more use here.

Follow the Links to get step by step info on how to replace the heater core on a mk 2

http://vwclub.co.za/vwforum/viewtopic.php?t=12737

http://www.clubgti.com/forum/forum_post ... =1398&PN=1

Good luck

Have done it on 2 jettas already and it is not too bad a job, just hated the jetta with AC that was a mission job. would do a non-AC car anyday..