Heater core replacement?

It looks like you will need to remove the dashboard because there is a mounting bolt at the top of the heater case. Also, you will need to vacuum down and recharge the A/C system. Here is a video to help show you how. Disconnect the battery and drain the coolant.

https://youtu.be/4EqdrBVb0sY

Here are the instructions on how to change out the heater core in the images below. Start by removing the upper dash mounting screws and the main mounting bolts on either side of the dash down low. You also will need to remove the steering column bolts as well. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can walk you through the repair.

Thank you Ken, can you explain to me why I need to vacuum down the A/C system?

You can see in the first diagram the AC hoses from the evaporator need to be disconnected..