Blown Thermostat Twice and Dead Transformer
Pretty much can guarantee either you've wired up your thermostat wrong, or that you chose a thermostat whose current draw on the connection to the A/C unit  exceeds the A/C port's rated capability.
Consider checking the manuals.
Then see if you can power the thermostat off a different source, such as a local DC supply, rather than hanging it off the A/C block.