Same basic system as a standard auto system. Instead of the evaporator in the cab, a small freon to water heat exchanger is placed in line. A water pump would be needed to circulate the water and the heater box would need work to manage the condensate. With the right valves, I think that even the heater would still work.
The A/C guy here at work is interested in trying it and has located the parts in A/C catalogs.
