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How to set up a 2.4Ghz smart device with a dual-band router

This is an annoying but serious problem, as evidenced by the hundreds of thousands of hits on the web regarding this issue.

The issue is as follows: You have a smart device (e.g. a smart light bulb, smart TV, smart thermostat, smart security camera, smart dimmer switch, smart plug, smart HVAC system, etc.) that only connects to a 2.4Ghz WiFi network, but your router is dual-band (does both 2.4Ghz/5Ghz), and your setup device, typically your mobile phone, auto-selects the 5Ghz band. In this situation, you can't set up the smart device.

Solution

To set up the smart device, you'll need: (a) a mobile phone that can provide a 2.4Ghz hotspot WiFi (this is typical), (b) a setup device such as another mobile phone or tablet. Then the solution is as follows:

  1. Unplug all other smart devices in your house.
  2. Turn off the house WiFi.
  3. Turn on the hotspot WiFi with SSID and password set to be the same as that of the house WiFi.
  4. Check that the hotspot WiFi is indeed 2.4Ghz. If this is not so, this solution doesn't work.
  5. Connect the setup device to the hotspot WiFi.
  6. Plug in the smart device.
  7. Connect the smart device to the hotspot WiFi.
  8. Set up the smart device [in my case, it was a Mitsubishi Split HVAC unit] using the setup device.
  9. Unplug the smart device.
  10. Turn off the hotspot WiFi.
  11. Turn on the house WiFi.
  12. Plug in the smart device.
  13. Plug in all other unplugged smart devices.

Note: While this looks like a lot of steps, it is safest, because the WiFi settings of your other smart devices may get confused by the WiFi switching. Depending on your other smart devices, things may work without the first and last steps.