drain the system ,,until
it real low,and remove the hoses from the out side of it,go inside and remove the cover,and then the straps,and remove the old core,,these one aren't too hard to do,,it just take a while to do it,,good luck i hope this help,s.,,have a good x-mas.
How to change a heater core in a 89 chevy astro van?
Drain Coolant. Remove coolant bottle, washer bottle and the hoses that attach to the core and plug open
ings. Remove core cover and retaining strap screws. Remove core and replace.
advice to tellmultiple tables