What determines when a two stage heat pump switches from 1st stage to 2nd stage? Somewhere I heard that after 10 min. it will switch to 2nd stage if the system hasn't satisfied the set point, but that makes little sense if best efficiency and dehumidification requires longer run times. Does the tstat make a difference? I'm using a White Rogers 90 Series Touchscreen on my current single stage heat pump so it will support dual stage units, but the manual doesn't provide much info.