Which Thermostat are you using that you're communicating to the Arduino with??
Thanks for your replys.The compliled sketch size is only about half of the availabe. 14950 bytes to be exact.I only count 3 String variables. Is this what you are refering to? Or are you talking about all the text in the Serial.print's?
It turns out the pin was being pulled low before the serial data finished sending so I had to add a small delay after sending out the serial command.