No harm will come from running the A/C at all. All it does in the long run is consume a little more fuel because it scavanges a little power away from the engine to run it. It will never overheat running the A/C unless your cooling system is in a horible state of no maintenance. Idling for more than 3 minutes is not recommended unless it can be avoided. If you idle the engine for prolonged periods of time (more than 25 minutes regularly) I would change your engine oil according to your severe use schedule in the manual. Idling also does not allow for full oil circulation, possibly in the long term experiencing bearing wear in the journals and races furthest away from the oil pump. So in short, if you are going to sit in place for more than 5 minutes, best to shut her off and head inside to shelter.
Believe it or not, NOT running your A/C is more harmful that running it. If it sits for a prolonged period of time without use, oils in the refrigerant do not circulate, lending itself to damaged/dry rotted seals.