So it turns out I got conned by the mechanic. He knew I was in another town, so wouldn't get back to him.
I was told he had replaced the heater control valve, when in fact he had removed it and just put two plain tubes in its place.
If i remember right there is a vacuum solenoid box under the dash on the passenger side, they are notorious for the hoses and connectors inside the box to disintegrate, you can open the box and re plumb it. You can follow the vacuum lines as all the actuator lines go into it. Be sure to take a picture of the inside before you start repairs.
First check the ...
This hasn't happened with any of the cars I have owned over the last 22 years - which is a pity, because one of the things I would have liked is designed functionality to do what Erik vanDoren mentions - setting the selector between positions to try and get this to happen.
In my more recent cars (last 10 years or so) it is impossible to get this to happen ...
NOTE: While it doesn't help with your specific question, I also agree that you should talk to the police about the damages.
My suspicion is that whoever was monkeying around with your wiring and electronics managed to cross several wires and blow some fuses. I would start with the fuse box unless you're certain that some of the wiring is damaged. If that'...
Apparently in addition to the two strips there is a smaller strip just below the heater panel with a locking button on it. You can loosen that and lift it down to release the heater panel.
This link appears to have more detail on the procedure.
This sounds like a voltage drop. The most likely candidates are:
the heater resistor
the heater fan
These components are usually located right next to eachother, in the footwell if the front passenger. The resistor can be electrically tested using a multi-meter (measure the resistance through all combinations of connections), the fan too.
Also check that ...