So when the air is blowing, is the heater working on all speeds ? If so first thing I would think that either the vents or heater core is plugged by a mouse nest. In that case you could either drop the heater assembly out or remove the blower motor and try digging it out from there. If your blower motor doesn't work on all speeds I would go after the resistor with is located next to the blower motor. As for the wiring mess I would repair what ever was done too make the cooling fans work.

 

The no run on setting 5 may be a bad blower resistor, but another thing to check is the vacuum line that runs along the fire wall and down the passenger side strut tower (See photo), the thin black plastic line. On three out of four of the gen. 6's I've had that line broke causing a vacuum leak and the HVAC actuators would not open causing weak air flow. Grab the line where it goes down beside the battery and give a gentle tug to see if the broken end pulls up. The line passes under the battery toward the steering pump where it goes into a large wire loom that passes through the firewall and into the cabin. You might find the other broken end about 4-6" into that loom after you remove the tape at the wye and open the loom.

Here's a link to a previous thread I posted on with pictures:
https://montecarloforum.com/forum/mo...k-tower-57414/