01 Silverado 1500HD, A/C on a toggle switch???

[GMCjet52]

Just bought a 01 Silverado 1500HD. After getting it home I flipped up the little door that covers up the 12 volt plugs and a toggle switch wired up to something fell out.

After messing around with trying to figure out what it does I noticed it was turning the A/C compressor on and off. Then I tried the A/C with the switch turned off and it didn't work. But works fine when it's turned on.

This switch will turn the compressor on even when the fan switch is in the off position.

What do you guys think the previous owner did and what problem did he have? I bought the truck from a dealer so I'm guessing he doesn't know about the secret switch.