We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember harry saying
something like:

Seems to me that a DIYer could make a heat pump

By arranging a bank of fridge/freezer guts to do the job.

The problem being evacuting and filling the system.

Not a single system- several unmolested systems arranged in parallel.
I've observed that many fridge and/or freezer systems can be removed
from the cabinets in one piece and pressed to another use; either as an
air/air exchanger or even heating a water trough.