ranch house with attic. the big pipe outside with insulation is not sweating other pipe is warm. in attic i took side covr off the unit to see if evaporator coil was dirty .it wasn't on the outside . didn't take the other panel to look at the other side wher the air from the house vent goes back in. also put my hand on the coil it wasn't cold just sort of cool. should't this coil be cold ?