Carol, sounds like you should have called the heating/AC people to fix your original problem-not the plumber. IF your unit is up in the attic and it sound much like the AC condenser on a convential central A/C system like we use in the south, the condensate drain sounds like it is clogged up....did your plumber confirm that the new drain pipe he installed was not plugged up as it drains into your house plumbing vent;drain system? and did he verify that the drain outlet out of your A/C unit was not plugged up or clean it out if it was? My unit has a backup overflow pan underneath to catch the water and drain it out an exterior soffit or wall if the primary pan and drain line are clogged from mildew, dirt, grime, etc. does your unit have the same setup??? Post up with more details of your configuration and what was done or not done so we can help with better suggestions.