Heater Core

You'd know if it was your heater core; with the heat on you will smell coolant. Should also be a fair amount of coolant leaking onto the passenger side floor out of the heater box. Hope it's NOT the heater core, because they're a beeatch to replace.

You cam order a new heater core from
www.50resto.com
Good Luck

Yea i would pray its not the heater core, that thing is buried behind the dash and a royal PITA to change.

To get to the core you will need to first remove your seats, then drop your steering column. then remove the center console. after that just unbolt your dash and gently pull it out. the core is in a small black box on the passenger side(if you need a better idea of where it is just pop the hood and look on the passenger side where the two coolant lines run into the firewall you will also need to disconnect these btw. after opening the box just pull the core out there should be nothing holding it in place besides the hoses in the firewall.
and most parts store carry the heater core still....... ie. autozone, advance, o'rieleys........

you better do it yourself, i was quoted $800 CAD for parts and labour