Manifold Heater for Cold Climates

i presume the summer in silver springs has the odd day of humidity. if it was icy on the outside it will have been colder on the inside

and your set up created, on some occasions, a considerable change in pressure from high to low
and your inlet acted like an aircon unit or fridge.
compression a restriction and then freedom for what was compressed, to expand

i.e expansion of previously compressed gas stole all the heat from its surroundings.
just this time it was your inlet not a bag of chicken dippers from costco that froze

conditions were just right

different season early evening, R in the month no problem.... but every now and again