Here's my take on the freeze trap:
Top Middle Bottom
█████WW█████ ████████████ █████MM█████
█++======++█ ███╬╬╬╬╬╬███ █++++++++++█
█+░░░░░░░░+█ +XƒƒƒƒƒƒƒƒX+ █+≡≡≡≡≡≡≡≡+█
█+░░░░░░░░+█ +XƒƒƒƒƒƒƒƒX+ █+≡≡≡≡≡≡≡≡+█
█++======++█ ███╬╬╬╬╬╬███ █++++++++++█
████████████ ███≡≡≡≡≡≡███ ████████████
████████████ ███░░░░░░███ █++++++++++█
████████████ ████████████ █████DD█████
+ Floor
█ Wall
░ Hole
╬ Fortification
= Retracting bridge, over hole
≡ Raising bridge, AKA Atom Smasher
ƒ Freeze zone
W Water Source
M Magma Source
D Drain
X Floodgate (optional)
It can only by two tiles wide, but could be as long as you want (using more bridges for lengths above 10) . The freeze zone of course will need to have all the ceilings above it channeled out. The holes on the top level will turn into ice walls when water fills the chamber.
All bridges are linked to a single lever. When pulled, the top bridges retract and water pours into fortifications in the middle level, and form there into the freeze zone. The magma below it has been atom-smashed, so the water freezes. The bridge on the middle level raises to prevent water from going down the drain.
When the lever is reversed the top bridges reappear to stop more water pouring in, and the bridge below lowers, allowing magma to flow in and melt the ice above. The bridge in the middle lowers to let the melt-water drain out.
The floodgates, if you use them should be connected to a separate lever. Their only purpose is to prevent a mess from the water, and they only need to be raised during thawing.
For what it's worth, I invented this independently, before I had ever heard of the degrinchinator.