where is heater core located

It's on the passenger side and you'll need to remove the dash the get to it. From the engine bay you should see two rubber hoses going through the fire wall and these are connected to the heater core.

Like he said, the heater core is behind the dash on the passenger side. The dash doesn't have to come completely out to do it, but close to it. You can bungee the bulk of it up out of the way and work behind it. In either case it's a very intensive job, in most cases a whole day or more.

If you need to change it it is behind the dash but you might need a Hines repair manual because there are several steps to do it and it is very time consuming I just had mine changed and it took the shop almost nine hour and it can cost a lot. At dealer up to $800, but small shop $300 to $500.

Also, you'll probably want to change the air conditioner evaporator while you have the dash off. Moisture tends to accumulate around the evaporator and corrodes the aluminum. Especially if the drain tube is plugged. (The drain tube is on the engine side of the firewall, below the heater core tubes.)