About the size of those high and low-pressure A/C lines

February 1, 2016 | By Staff


I’m pretty sure there is a typo in December’s Mechanic on Duty column. In the letter from Russell Jansen from Phoenix, he inquires about adding A/C to his ’56 Chevrolet. In response you detailed the highlights of the installation and said, “High-pressure hoses are bigger in diameter, and low-pressure hoses are smaller”—when, in fact, the opposite is true. The vapor, suction, return or low-pressure line—by nature of its function is always larger than the liquid high-pressure line on a conventional automotive air conditioning system. My guess is that most folks know this from experience. But just to eliminate any confusion, you might clarify.


You are correct, John. The high-pressure liquid hoses are smaller, but when the liquid is decompressed and becomes a gas, it is fed into the larger diameter lines. My statement was incorrect and misleading. I hope when a reader receives a kit to add air conditioning to his car and looks at the diagrams showing the installation, the situation will become clear. In the end he can’t hook it up wrong, though, because the fittings are different on the two types of hoses.