You will have to contact Kelvinator for the port forwarding details. I've had a brief search and can't even find a hint at what it might be.
In the mean time, at least for testing, you can use DMZ instead of port forwarding. In DMZ set the internal host to the IP address of your AC, and that will allow the AC to connect to/from the internet without any firewall interference.
Yeah it's a bit of a black hole of information from Kelvinator! I emailed a request for the details last night so hopefully they come through with the goods, might get on the phone tomorrow and pray I get someone who can point me in the right direction!
Will give the DMZ tip a try, appreciate the assistance
So just to update, even in DMZ it still won't connect.... Everything works great while connected to the Wifi, just nothing when I try to connect my phone without it. Even tried deleting and reinstalling the app as @petergdownload suggested to no avail. Incredibly frustrating!
If its not working with DMZ then the only thing I can think of is that you running into a known issue of the 5366 TN/LTE when accessing the local network remotely. Usually that problem (a lack of NAT Loopback support) surfaces when the public IP address is used on the LAN and not when the device is actually accessed remotely, although there have been some reports where that seems to have been the case.
As a work-around, i've linked the home comfort app to google home via a nest mini, tested it last night and it works a treat! If nothing else i have a solution that works but would definitely love to know why the app itself can't connect, i'll have a look into 5366 TN/LTE issue you mentioned.