How to identify a/c low pressure service valve?

Answer by  lule (166)

You should put hand on the lines. The low pressure side is colder if the valve is operating. If valve is not operating, than you can decide by the size of the line. The larger is with lower pressure.

Answer by  kipcat (1964)

The low pressure side, or suction side, will be the colder of the two lines when it runs. If it is not running, it will be the larger of the two lines going into the condensing unit. It will still have a pressure of 30 - 90 psi, so it really isn't low pressure and should be treated with care.