You have an aftermarket heater, the two common heater options look like this.
http://www.flickr.com/photos/advance-design_parts_co/8129448404/in/set-72157631868452754As stated to kill the heat you will have to stop the coolant flow. They build quite a bit of heat without a fan and some will drive you out of the cab with a fan. Most heaters are easy to remove should you want to see how to hook it all up. Most have just one or two wires, various fan arrangements, a simple switch, that's about it. I have found well over a dozen different types of aftermarket styles, Firestone, Stewart, B.F. Goodrich, Sears and Montgomery Ward to name a few.
