Sometimes, if your deployed power requirements are greater than your PP produces, your life support shuts off when you deploy weapons. I have an icourier that does this - I just treat it like a battle timer challenge! 7:30...
With all my shields, boosters, PA, and rails, my FDL takes a huge amount of power. I put things that aren't critical to combat (Cargo hatch, FSD, life support) on priority 5 so they shut-off when my hardpoints deploy. Prior to engineers, this was extremely common as power plants were limited to stock power. Nowadays, it's more rare since you can over-charge your PP. However, I have a really cold, decently armored PP that I don't want to change, hence I saved power by turning off life support in combat. It does alter combat a little as sound is muffled, but you get used to it quickly.