If you remove the fan, the controller is built in to it.
you sholud from memory be able to test, the contol panel switches.
you should have pos,and neg, and the other wire you sholud get a vaiable voltage depending on where the switch is. it may be that it is stuck high, but I would put my money on the fan/resistor controler.
I also have a feeling that some of the digital/ a/c systems have another fan on the drivers side.