Probably inadequate airflow heatload going through the indoor coil.
So Z-Bail...did you have long term success with this? Reading your posts were like looking in a mirror, almost to the letter. I caught on to running the blower on "on" early on.
It would cool for 7-10 days, but ultimately freeze over again. The tech always instructed me to run it on auto and within 24 hours the coil/TXV would freeze.
Just replaced the t-stat, ran on auto and it froze the next day. Tech is thinking it's the board for the blower. He's stumped and has brought it to his companies tech group. Would love to hear if you had long term success.