With regards to abnormal pressurization on the ground in freezing conditions:
I'm not familiar with the G150 or it's pressurization system however on aircraft which rely on an ejector to provide the vacuum to open the outflow valves (as they should be on the ground prior to applying takeoff power) , if moisture happens to be present in the service air system supplying the ejector and is allowed to freeze this can potentially reduce or prevent vacuum production. This in turn allows the outflow valves to close and subsequently, assuming doors/windows are shut, pressurize the cabin with little or no control. Something to be certainly cautious of in cold weather OPS.