Unidentified relay

[starbuckk]

When I got my truck many years ago it had a broken control module for the heating/ac system. This was back before GM started making replacements again. Since the AC switch was tied to this broken module, some rewiring was done. A toggle switch was added and the AC power was routed through it. The thing is, there was a wire tapped off the AC fuse to this switch, which then runs direct to the AC.
Also, it looks like the purple wire is supposed to go to the unfused port on the fuse box but I see an orange wire there instead. I have not tried to trace any other wires.
What exactly do the resistor and relay do?