I'm not familiar with the puma engine but here goes.
what fuse does it blow? is it the fuse for the aircon pump clutch or a random fuse.
with the engine stopped..! can you remove the drive belt for the aircon(my 300 has a separate belt for the aircon)
then start engine and switch on the aircon, if the fuse blows you know its a wiring short, if the fuse does not blow you know the aircon pump or clutch is the problem.
I have seen the pump clutches size through mud ingress, with the belt off, IGN on, & engine not running you should hear the clutch click(LR - clunk
) when the aircon is switched on, the aircon pulley should "freewheel" easily until the aircon clutch pulls in, then the pully should turn easily but you should feel the drag of the fluid.
hope this helps