A 30-second hardware self-test for the Faikout module. Linking the module's Tx pin to its Rx pin puts it into loopback mode: it sends data to itself and flashes the LED in a repeating red, green, blue sequence. That single test proves three things at once, the serial transmit, the serial receive, and the LED, all working independently of the air-con, the cable, and your WiFi.

Use it to tell a faulty module apart from a cable, air-con, or configuration problem before going any further.

1. What the test proves

With Tx joined to Rx, anything the module transmits comes straight back into its receiver. The firmware recognises this loop and drives the LED through red, then green, then blue, over and over. If you see that sequence, the module's transmit line, receive line, and LED are all good.

It is a test of the module only. It does not involve the air-con, the cable, the WiFi, or the MQTT broker, which is exactly what makes it useful: it isolates the module so you know whether the fault is in the module or somewhere else.

2. When to use it

• The module seems dead or unresponsive and you want to know if the hardware itself is alive.
• A unit reports "offline" or "no data tx/rx" and you need to narrow down the cause.
• You are checking a module on the bench before fitting it, or after a suspected fault.
• You have a known-good unit and a suspect one, and want to confirm which module is at fault (run the loopback on each).

3. What you need

• The Faikout module.
• A short jumper, a single Dupont lead with a socket on each end, a piece of wire, or a header link, anything that can bridge two pins.
• A way to power the module: the air-con's low-voltage power pins, a 4 V to 40 V bench supply, or 5 V over the USB test pads on the latest boards. (The air-con normally supplies about 12 V.)

You do not need WiFi, an MQTT broker, the cable to the air-con, or any software for this test.

4. Safety first

Always isolate the air-con at the mains before opening it or going near the electricals. Some Daikin connector types carry dangerous voltage in normal operation.

For the loopback test, the simplest and safest approach is to do it on the bench with the module disconnected from the air-con, powered from a separate low-voltage supply or USB. Never bridge pins on a connector that may be carrying mains-derived voltage.

5. Running the test

1. Disconnect the module from the air-con (or remove it from the unit) so its Tx and Rx pins are free.
2. Find the Tx and Rx pins. They are labelled on the board, the same pins you would normally wire to the air-con's serial connection.
3. Bridge Tx to Rx with your jumper. Make sure it is a solid connection and that you are joining Tx to Rx, not two of the same pin.
4. Power the module: 4 V to 40 V on the Power and GND pins, or 5 V on the USB test pads. A brief solid green at start-up is normal.
5. Watch the LED.

With the link in place the LED should settle into a continuous red, green, blue cycle within a few seconds. (If you previously turned the LED off with the dark setting, do not worry, loopback and offline states still show.)

6. Reading the LED

The only result that confirms a healthy module is the repeating red, green, blue cycle.

7. If it passes

The module is fine. Its transmit, receive, and LED all work, so the problem is elsewhere. Look at, in rough order:

• The cable between the module and the air-con (wrong type, damaged, or a poor connection).
• The air-con port itself, and that the module is plugged into the right connector.
• WiFi or MQTT configuration, if the unit powers and runs but will not connect.

Remove the Tx to Rx link, reconnect the module to the air-con, and carry on troubleshooting from there.

8. If it fails

No red, green, blue cycle means the loop is not getting through. Work through:

• Check the jumper actually bridges Tx to Rx, with good contact at both ends. Re-seat it or try a different lead.
• Confirm the module is really powered. Is there any LED activity at all? A solid green flash at start-up tells you power is reaching it.
• Try a second jumper in case the first is broken.

If you still get no red, green, blue cycle with a known-good link and confirmed power, the module's serial or LED hardware is most likely faulty.

If you have a second, known-good unit, you can confirm by swapping the suspect module onto it and running the loopback again. If the module still fails, it is the module. Contact Faikin Australia and we will sort out a replacement.

9. Loopback is not a factory reset

These are two different procedures, do not mix them up:

• Loopback test (this manual): bridge Tx to Rx. Tests the module hardware. Nothing is changed or erased.
• Factory reset: briefly short the two solder pads on the back of the module three times within three seconds. This clears the WiFi and password settings. Use it only when you are locked out or need to start the setup again.

10. Quick reference

Source: RevK ESP32-Faikout Setup manual (codeberg.org/RevK/ESP32-Faikout). Behaviour described matches the firmware as of June 2026.