Electrical – Two Fans on One Wall Switch

The simplist solution is to replace the fan/light combinations with modern units that have wireless remote controls for both light and fan, and include multispeed settings for the fan.

Your current setup probably has a direct hot connection to the fan with a single pair of hot wires going to the switch for the light. This switch could be converted to turn the fan and light on or off together, but not separately without running additional wires.

You could snake new wires in to have separare controls for fan and light (a cable with three wires would do with a double switch), but this is requires routing cables through the walls and patching the plaster/wallboard after installation.

This also would not give you three speed controls at the wall. The three speed switches in most fans (those that use pull chains instead of a wireless remotes) cannot easily be controlled by a wall switch without a significant change in internal wiring, not a job for a novice.

A retro conversion could be done, but a replacement may be easier and maybe even cheaper than hiring an electrician to do the rewiring (remote fan/light combos can be had for less than $100).

Comparing those tables: Note that the speed switch in the circuit you show isn't using L.

A: L+2+3 
B: L+1+3 
C: L+1      (Maybe this is L+1+2 ???)
D: L+1+2+3

0: No connection (or no connection to anything but L)
1: 2+1 (possibly plus a connection to L)
2: 1+2+3 (possibly plus a connection to L)
3: 2+3 (possibly plus a connection to L)

Making them correspond with each other...

C is obviously equivalent to 0.
D is obviously equivalent to 2.

That leaves us with

A: L+2+3 
B: L+1+3 

1: 2+1 (possibly plus a connection to L)
3: 2+3 (possibly plus a connection to L)

We can make those match if we relabel the connections. If we just swap the labels on your terminals 3 and 2, then

A is equivalent to 3
B is equivalent to 1

If we renumbered them all (your 2 is their 3, your 3 is their 1, your 1 is their 2), then

A is equivalent to 1
B is equivalent to 3

Pick whichever you prefer; one will switch off-high-medium-low-off, and the other will switch off-low-medium-high-off.

As far as theory goes: I'm not sure either, but let's see what I can do with it.

3 (2->3) appears to be "slow" because power flows through the right half of the bottom coil, and then through the side coil, in series. More resistance, less current flow, less power.

1 (2->1) appears to be "fast" because the left side of the bottom coil, and the side coil, are powered in parallel. Both get the full house-current voltage applied across them rather than the reduced amount of power they got in series.

2 (2->1 and 3) is the tricky one. I am far from certain, so DON'T take my word for it. But I think what's happening here is that, since the middle and right sides of the bottom coil (1 and 3) are now connected to each other, that loop has a current induced in it by the motor's moving magnets, which creates a countering magnetic field, which acts as a magnetic brake to slow the motor... so fast with a bit of braking equals medium. Seems like an odd solution, but if I'm remembering my freshman Physics at all correctly it might actually be a reasonably efficient solution.

You might want to run this by the physics discussion, to get someone with more recent memory of electrodynamics to check and/or correct that last paragraph.

Gopher baroque...