Unstoppable Blower

I have a 1994 Park Avenue that was sitting for about 6 months. The temp guage was not working for an unknown amount of time. I replaced the sender and started the car. The temp guage worked. The heater blower started at slow speed as expected and went to high speed as the car warmed up. But then it would not respond to controls--not "off", not fan speed control. Environmental control will switch from heat to A/C in "auto" mode based on temp setting, but blower stays on high regardless. Blower stays on high even with ignition switch off and key out. I had to unplug the electrical connection to make it stop.

The environmental controls seemed to work normally before I installed the new sender. Could it be that the temp sender also feeds the environmental control logic and caused another switch to open somewhere that is now stuck open? My guess is that it is a mechanical switch problem versus a computer problem otherwise it would shut off with the ignition. Any ideas would be appreciated.

In case anyone is interested in the outcome...

The problem was a blown fan control module. I have since seen a description of the location and fix elsewhere in this forum so I won't go into that again. I would mention that I had seen the FCM quoted at $100-$150 in numerous places, but I found it for lots less at www.expressautoparts.com. First needed to get the right part number from www.acdelco.com.