This is kind of like asking what to expect with a woman. Every woman is different, or in this case every employer is different.
You'll be expected to: work hard, show up on time, stay late when asked, do what you're told, think for yourself and watch, listen & learn as much as possible.
Don't get defensive or nod your head and say "yah, I know... I know!"
For your own sake try not to talk about anything but HVAC during your 90 day probation period. ie; don't give them ammo to lay you off.
Hope this helps
"Quality is never an accident; it is always the result of intelligent effort. The bitterness of poor quality lingers long after the sweetness of low price is forgotten" --- John Ruskin