Back in the engine compartment, the firewall has to be modified to fit the new A/C unit. Vintage Air really helps installers out with the included templates that show where to cut, and where NOT to cut. Here you can see the amount of firewall that needs to be removed using a small saw or grinder. If your cut isn’t exactly perfect, use a small die grinder to make it work. Also wear a mask so you don’t breath in a bunch of fiberglass dust, not good for the lungs!