The Nano is fine to connect directly because it has diodes on the data pins but the S3 Lite needs a level shifter or it'll eventually stop communicating with the air handler.

yeah came here to say this, I have my mini splits set up on the S3 light with level shifters, not worth skipping because they'll end up failing on you - requires a little soldering but nothing complicated

wiring:

1. Mini split black (GND) → ATOM G

2. ATOM spare G → shifter GND (either row)

3. Mini split red (5V) → ATOM 5V

4. ATOM spare 5V → shifter HV ref

5. ATOM 3V3 → shifter LV ref

6. Mini split yellow → shifter HV1

7. Shifter LV1 → ATOM (G2 / GPIO2)

8. Mini split white → shifter HV2

9. Shifter LV2 → ATOM (G1 / GPIO1)

if the gpio ends up being reversed you can handle it in software