Many heat pumps just don’t have UARTS (byond JTAG headers). Still, one can get at the operational data with the IR remote and display. The TX/RX pins described above sound like the scheme on my unit (an air to air unit). Also, that wifi connector they sell … dont think it has any more functionality than the remote! Anyhow, thought i’d share my project, it hacks IR protocol and display interface and routes data as MQTT client with ESP8266. It works with Senville, Mr.Cool, Pioneer, Lennox, and some Daiken i expect. Basically, all brands using same hardware (there are a bunch) https://github.com/kpishere/homie_heatPump
Some pics in the wiki https://github.com/kpishere/homie_heatPump/wiki