So far as I can tell, there's no indication of LP ground connection to the aircraft. Normally we coordinate with the ground crew via interphone so as to not have both APU bleed and LP air providing the packs simultaneously.
Indication of the air cart actually providing conditioned air can be seen on the COND sd page. The zone duct temperature indication shows an according value (i.e. not 30 degrees or something like that but an actually comfortable temperature)