Adam Savage did a video where he worked with a guy to build a cooling unit for a cosplay suit. They were using custom compressors that were actually pretty efficient, which makes a lot of sense if you're going to be battery powered.

I think some manufacturer names were mentioned? There are units now with with variable compressors, so you run them constantly at low current instead of full blast. If you want to build your own fridge, just to build one, I'd maybe look at those.

The efficiency of a heat pump is relative to the delta-T you're trying to push. If you are trying to hit 40° sitting in a 72° room? You could probably repurpose a portable unit for that, sure. If you're trying to bring ambient down to 40° for a cabin? I think you're right to be concerned if it's up for it.

There's also the defrost functionality which you won't have.

Re: the cosplay suit — were they essentially trying to recreate the cooling system on EVA suits?

Well, not exactly. Costumes can just be suffocatingly hot. Bulky, poorly ventilated, possibly used in an environment that isn't air conditioned. If the SFX crew for your movie is on their game, you have a cooling system built in and it's not that miserable. But I've heard stories of some people properly suffering in particular roles because it was just so goddamned hot.

If you go to a convention, like Adam is fond of doing, you're gonna be suited up for hours, without support crew. So it's gonna be tricky, and he makes money doing videos about tricky things...

That said, he did start with a surplus EVA (or was it fighter pilot?) base layer with the cooling tubes built in.