The heater box is held to the firewall by five bolts. Four are attached directly to the firewall, at roughly the four corners of the heater box. The fifth is a brace underneath the box, near the airbag sensor/radio area.

Once the bolts are removed, the box will be quite effectively attached to the firewall by all the sealing compound used at the factory. A prybar or BFS is necessary to gently lever around the perimeter of the box and break it away from the firewall.

The box can be pulled with the expansion valve still attached, there is plenty of room to pull it through the firewall.

Don't forget to disconnect the heater core hoses.

- JimY