That drove me nuts on my non-ducted as well. I installed a new control unit so I could control it with the thermostat. Toughest part was running the thermostat wire to the unit as mine was not ran from the factory.
The uTube vid below is essentially what I did except I used a standard battery powered house thermostat that I had already installed. Because I used a house thermostat I only have 1 fan speed though so I chose low.
https://www.youtube.com/watch?v=BR8To1Yt2xQ&t=570s&fbclid=IwAR1bB_lReNtcD4zp0umOvr2maYu9GS4LWQW2CR6J-ZjXGdWAraZLv8RldJU