Not a physics student -- but was thinking about how the A/C system works in a vehicle. First surprise was that pressure drops when a tube narrows. Seemed counter-intuitive as I was picturing taking a balloon and squeezing it -- would the pressure in the middle be lower than the ends? Then again that's a closed system, but it affected my thought process. Perhaps a garden hose is a better example. Sure, the water speeds up, but it certainly doesn't feel any easier to squeeze a garden hose (say a wide but flexible one) with water running through it. The more you squeeze, the harder it would get because you're constricting the flow -- is it not inner pressure making it harder and harder to squeeze? Lastly, I understand that the refrigerant (R134a) in a cooling system needs to expand to cool, but I definitely do not understand how constricting it into a tiny section allows it to expand and become hyper-cooled gas. A) Where is it expanding to? How is there sufficient room to expand in the constricted area? How does this not increase pressure? B) If the total pressure in the system remains the same (dynamic increases, static drops?) then why is the refrigerant phase changing? In other words, if the total pressure remains the same then why does the boiling point decrease at all? Apologies if the questions are stupid. Would really love to understand the most fascinating part of what makes A/C possible.