small tube high side, big tube low side.
At low speeds the car will rock from side to side.
On a R134a system the low side service port is the smaller one.
The low pressure side is usually the fatter tube of the two. That's how it is on my '97 3.9.
The car will lurch side to side at low speed. The tire may have a visible distortion. The belt might stick out of the tire.
You check the ac system on a f-250 throught the low side port. This will tell you if you are low in refrigerant. If you are not low then you might need to get a manifold gauge set to troubleshoot it throught the low and high side. There is a website that has helpfull information about your vehicle ac system www.idqusa.com.
on the passenger side right by the fire wall you will see a nozzle that looks like a valve on a tire, that is your low side where you put your coolent. Follow the hose from the compressor and it will take you right there
LOW side
There is a web site www.idqusa.com that will tell you were the low side port is located on a 97 Malibu. Just click on the locate low side port. There is much more helpfull information about your vehicle ac system as well.
Low side.
High side and low side refer to the pressure in the ac system. Ie The high side is the high pressure line and low side is the low pressure line.
The low pressure port usually has a blue cap on it. The high and low pressure ports are different sizes so the they can not be accidentally interchanged.
The low side will be on the accumulator and the high side will be on the discharge line.....