I have a carrier gas heating unit is in the atic and the drain line (pvc) drains outside down the wall I have insulated the pipe but at the bottom it freezes up when the water starts to swril around about 2 inches off the ground and to the ground -- this stops flow and stops the furnice what can I do -- I tried to run pipe insulation to the ground and our few inches but still freezez at the end of the insulation

Cut off the pipe some so there is a bigger distance from the ground to the pipe OR redirect the pipe to a indoor drain for the cold weather so it has no chance of freezing. Building codes need to be considered eventually but for now you just need to keep the furnace running.