Never, do not let anyone touch it if it's working. The furnace, yes...the outdoor unit, NO. Even then, the furnace would just need filter changes, and maybe checking gas pressures for heat and heat exchanger cracks or whatever..
It's a closed loop system. Zero reason to even look at it unless it stops working.the more it gets worked on, the higher changlce it won't be working the same after.
Full darkness is most certainly a thing and is more of a thing then light..light is artificial. Remove the sun...what do you get, full darkness. Light is added, darkness isn't.
Same with heat..everything is cold unless heat is added.
Cold and full dark are forever, heat and light are techcially temporary.
Are your Huskies paws scratchy or smooth? Curious as mine are kinda scratchy like a cats tongue but they have never seemed to bother her. I always figured it was a breed thing.