Have a 26yr old 15-tonne electric powered HVAC unit. Recently, A/C portion has failed. No way of repair. Fan still works, heating coils still work.

Need to provide A/C to a 1.5-2 story work space. No real money, and no means to fix or replace HVAC unit without major cash injection and taking out heritage walls, or current office construction.

I know, horrible situation.

Any possibility that I can get a few off-the-shelf ~15k BTU A/C units, blowing their cold air into existing ductwork (fan still works) and vent hot air into HVAC return? Can't vent through any window or wall. Trust me.

Is this idea stupid/how stupid is this idea?