There used to be companies who fitted after-market systems, but they may have been stopped by the emission laws.
You see, when air con is used the fuel mixture has to be altered by the ECU to maintain performance and tickover, so besides fitting a compressor, condenser, arranging the cooling fan to run in conjunction with the aircon, altering the drive belt system, running in the pipework, altering the wiring/fuesbox, changing the heater box completely.....you may then need to change the control module to make the engine cope with the extra load ........
But apart from all that, a vehicle with air con is great in the summer, even in winter it can be used to clear windows quicker than normal
