Much like the fortwo 450, the Roadster uses bowden cables to control much of the heating system.
A bowden cable is exactly like the brake cables you had on your BMX when you were young.
It's a steel cable running through a sprung wound metal tube, all covered in plastic.
When 1 end of the cable moves, the other end moves.
On your bike, the bowden cables only pulled and never pushed so the only issues you had back then
was frayed cables not sliding, rust inside the cables stopping movement and the cable eventually snapping.
However, on the Roadster, these cable don't just pull, they also push.
Although there isn't much force being put into the cables, it brings in the problem of kinking.
Over time, the internal cable can bend at the ends where it isn't in the sheath.
You will have almost no chance pushing a kinked wire and a small chance of pulling a kinked wire.
Below are the 4 heater controls.
1 - Recirculated or fresh air
2 - Heater temperature
3 - Heater output direction
4 - Blower power
Of these, controls number 1, 2 and 3 use bowden cables to control the various parts of the heater.
Control number 4 is just a plain switch. If that's not working, look here.