Most airports now prohibit the use of APU on stand for more than a few minutes. Many 'helpful' ground agents will connect conditioned air without consultation, for this reason it would be prudent to select the pack switches to off as per the warning in the supplementary procedures -
Ground Conditioned Air Use
Before connecting ground conditioned air:
PACK switches ............................................................ ................OFF Packs can be damaged if they are operated while ground conditioned air is connected.
After disconnecting ground conditioned air:
PACK switches ............................................................ ...... As needed