How to know which RX/TX pins to solder?

[optimusprimespace]

You have to guess which on is it or there are some recommendations to consider? Because it is hard to desolder these little pins if you've got it wrong.

[rrelande]

I assume you are referrring to USB pins. They are numbered 1,2,3,4.
pins 2 and 3 are the TX/RX, 1and 4 are Vcc and GND

depending on the model of the airco, you will need to solder according to model 1 or 2
for Midea

For Haier and similar:

i hope this helps proceed