Replacing a Heater Core on 1991 Chevrolet Astro

where can i find a schematic for replacing a heater core in a 1991 Chev Astro van?

2 answers
I'd recommend one of these resources:

http://bit.ly/autozone_repair_info
http://bit.ly/alldata_repair_manuals 
http://bit.ly/mitchell_repair_manuals_online
DO YOURSELF A FAVOR AND TRY PUTTING A TUBE OF ALUMASEAL THROUGH YOUR SYSTEM FIRST. 9 TIMES OUT OF TEN IT WILL CURE THE LEAK.