While I was making a spark plug for igniting fuels, I noticed that TESC can produce negative temp lightning, which cools the air. So I decided to put together a quick save demonstrating this (ambient heat must be enabled):
TESC with radius 0 (1 pixel) will produce absolute zero lightning.
That is true, if it is not within a few pixels of another TESC. I have done extensive testing of this. Also I have proof of this behavior in the linked save.