I have a 2006 Silverado LT3 Crew Cab with 67K miles. It has the auto dual zone A/c and I've never had trouble with the system or the truck I was out of the country for about 2 weeks (truck parked in driveway unused) and when i came home the truck battery was dead...not sure why but it was. Charged it up and it started fine but now the HVAC blower runs even with the ignition switch off and key removed. Only way I can keep it from running down battery is pull fuse which i have done. With fuse in, fan runs constantly with key out and if engine is running then fan switch operation in manual mode (bars 1 to 8) has no effect on fan speed - always on high.
I've seen a number of posts regarding this issue that seem to point to blower control module located near blower. With fuse in I get a constant 12V from 2 wire harness going from blower control module to blower motor and 12 volts between black and red wires on 3 wire harness going from vehicle to blower control module. Measuring voltage between purple wire and black wire on 3 wire harness I get 5.22VDC at lowest fan speed (1 bar) and 1.62 VDC at highest fan speed (8 bars) with gradual changes in between for speeds 2-7.
I don't mind replacing the blower control module (about $60 from Rock Auto) but I'd like to be reasonably sure that that will fix the issue and that there isn't something else going on.

I know there was a recall on the manual A/C models (CJ3) but mine is an RPO code of CJ2.

Called dealer and they just say bring it in but I'd like to have as much info as I can before I do that and I'd only do that if it might be something other than BCM.

If anyone has any ideas or additional diagnostics I should do, I'd sure appreciate some info.

Thanks,
Mike in AL