Glueing polycarbonate to aluminium

No. Araldite is not effective at gluing polycarbonate

Hot glue might work..

Or an acrylic sticks like s*it stuff might as well.

Hard to say without more detail.

Like whether its to come apart later on..

Or cyanoacrylate (superglue). Or silicone adhesives.

Not usually successful with metal

Or silicone adhesives.

better..

I thought double sided tape is what is normally used to hold stuff for temporary fixes.

I've very little information - as I said, this is in France and the people trying to do the job don't know much about such things (if, however, you want the aircon repairing and recharging on your private train...). I get the impression that it's a bond simply to hold the 2 parts whie the rest of the job is done, but unlikely that the parts will need to be, er, parted. I'll take some superglue, epoxy and possibly DS tape in with me and suggest that they're tried on an offcut.

If it is just holding together until bolted ... then superglue is probably best

I hope so - I'll give her 3 bottles of superglue (damn, another 75p down the drain!) to take back and we'll see what happens.