Sticky black liquid coming from Furnace / AC Unit
Has the combustion been checked on this furnace recently and is the heat exchanger in good shape. Are there any odors in the house, people getting headaches, nausea, etc. If he said that it looks like it is coming from an old drip pan made of tar get someone else to check your system. You may need to gain access to the duct work to find the source of the black sticky stuff.