There's a very old ceiling fan (without light) that I would like to replace with a new ceiling fan that has a light. I took off the switchplate to see how many wires, and there are three (black, red, green). But it's a pretty old-school Nutone switch with a transformer on it so I'm not really sure that the wires would support separate fan and light controls at the switch. Can someone here please advise? I'm hoping the image I'll try to post here works...
You might even be able to add a light to the existing fan; many are/were wired for lights and it's just a matter of using a threaded nipple to attach the fixture and connecting it to the wires provided for the purpose.
If you do need to replace the fan, you should probably replace that controller with a simple switch. You would then use the fan's pull chain to set its speed and a pull chain on the light to turn it on and off, or wire in a modern remote control box.
Very doable; I got fans without lights and added fixtures to suit. One I left on the existing wiring and I do use the chains to control its modes. For the other it was easy for me to pull new wire, so I set it up with a 2-switch unit, one for light and one for fan, though the chains also exist for fan speed control and so I can kill the light from bed. ;-)
I assume you want two switches, one for the fan, another for the light. From your description this would not be possible with the wiring you have. You are one wire short. In order to control both light and fan separately you need an individual hot wire going from switch to fan, and from other switch to light. I would recommend going with a fan with a remote. The fan is powered the same as your old fan, but the remote controls the fan and light separately.