I had a look for this, it's not blindingly obvious at all, it seems that only the overheat relays can switch off the trim air system either by a genuine overheat or turning out of auto or trim reg off.
It appears that the ZTC would attempt to control whatever it is dealt with. Although the references to "backup" modes are really confusing i.e. not differentiated between PTC & ZTC.
Any one pack in stby appears go to relay control of it's components and also into a 40°F protection mode via a standby card which doesn't appear to talk to the ZTC.
However there is one annoying statement that the ops of the ZTC rely on packs being selected to auto and then is simply never refferred to again.....
Will continue looking.
