Health and Prevention. The compressor fan works and the copper pipe going into the house is getting cold with condensation. Pipes in basements or attics are not the only ones that may not be properly insulated from the cold. Refrigerant is piped between the two components with copper tubing. This is because when the gases used to create the cold air are compressed they must be returned to heat to expand to complete the cycle. Pipes that are located in areas that do not have proper insulation, such as basements or attics, may need extra insulation to keep from freezing. An ac unit that has copper pipes can freeze up just as other pipes can freeze up. The conditions of the pipes never differ, the small one is always cold and the large one is always room temp, nothing more and nothing less. is not cold to touch, but the thin line (high pressure line?) There is another pipe that slowly drips water outside when the AC is on. My ac unit is not cooling, the large copper line is cold but not super cold, [ 7 Answers ] My ac unit is not cooling, the large copper line is cold but not super cold, my husband changed the filter and we set the ac to 78 and it has been at 81 for about an hour. My ac unit is not cooling, the large copper line is cold but not super cold, my husband changed the filter and we set the ac to 78 and it has been at 81 for about an hour. The large one carries the cold freon and is wrapped to prevent water from condensate on then dripping from the pipe. What’s worse than an air conditioner that doesn’t work at all? have an ac system- condenser/comp unit is on top of a high rise condo, so havnt gone up there yet. the return one is warmer (but still cool) and does not need insulation. An air conditioner not blowing cold air is one of the most common HVAC problems we get here in Florida. All AC units have an air filter which you can see from outside. How to Fix Sweating Copper Pipes. The hot summer months are very taxing for even the newest air conditioning system and if it is not properly maintained it can break down. The noise goes away after the pipe cools off, so i think the noise is the acutal sound of the water in the pipe. What other things should we check for before we call an AC …