I’m trying to switch from a single switch to a double switch so I can turn on my fan and light separately. I’ve got one hot switch and one other black wire.
The white lines are tied together so I’m assuming they’re neutral and don’t need to be looped into the switch.. but any combo I try of changing around those two black wires still turns on both the fan and the light at the same time.
All help appreciated
A1:
If you have only one switched hot wire, you cannot control the light and fan separately just by getting a double switch. You would need two switched hots.
If this wiring is in conduit, you would need to pull one more wire from the switch box to the ceiling box. If this is NM, you would need to pull a new cable with another conductor a 12 or 14/3 + gnd (black, red, white, gnd).
One conductor (say the white, with a black mark or tape to indicate hot) would carry the always hot from the ceiling box to the two switches, one (say black) would take a switched hot to the fan and another (the red) would take the other switched hot to the light.
Another solution to controlling the fan and light independently is to get a wireless controller which uses a single hot input (can use a switched hot and just leave the switch on) but has separate outputs for the fan and light.
With only one switched hot you must use the pull chains. Leave the fan pull chain off and the light on and the wall switch controls the light. If you want the fan in addition to the light, use the fan pull chain. If you want the fan only, turn off the light with its pull chain.
A2:
The first problem is the junction box in the ceiling. It may not be rated for a ceiling fan. Ceiling fans create a huge amount of vibration, and require a much tougher junction box. It’s possible to retrofit a ceiling fan box where the old box was, and there are quite a few Q&A about that here.
I suspect it’s not a fan box because if it was, you’d think the builder would run /3 cable (black white red) from the switch to the box.
Anyway, your dual switch simply will not work. It doesn’t have the wires it needs (black white red to the fan). You have a couple of options.
An accessory fan control module that sits up in the fan housing, and controls each separately. The module matches up to one of several control methods:
a matching, custom switch assembly that installs in that location
a wireless remote control
a plain switch, but certain patterns of flicking the switch on and off.
The fan control module is part of a “Smart Home” technology suite such as Insteon, HomeKit, etc. and you control it as part of that system – via Alexa, your phone, whatever.
As Jim discusses: pull a new cable, or go to pull chains.