Vertical Speed:
That is exactly the wrong technique. The smart thing was to start the APU and then run the pack(s) at Fully Cold for several minutes (regardless of how cold it already was in the cockpit/cabin) so that any possible !!!!! went overboard before any heat was introduced into the system.
I never had a problem in almost 20 years and I am delighted to report that I am still in the rudest of health (so far anyway).