Is a P-Trap needed before connecting a hose to drain water from air conditioner to sump pump?

You can not go wrong using a p-trap on any system.It may not need one it depends on a number of different things, Odors, static pressure in duct, local codes. If your duct has a high static pressure then the air will blow harder out the drain line if it is on the leaving side of the blower and suck in more air if it is on the entering air side of the blower . Mike