Tangentially related, I have an old residential absorption A/C unit. 3 Ton, fired off natural gas. 1960's vintage. It's a neat piece, and I intend to get it running for demonstrating the technology to students in our HVAC program where I teach. We exclusively cover vapor compression refrigeration, it would be nice to at least show them absorption.
I'm a professor of HVAC, have a degree in HVAC, hold a refrigerant license and a master mechanical contractors license... but I haven't had any luck finding ammonia refrigerant (R717) for sale anywhere.