[jyl]

I’m only pulling vacuum on one lineset at a time. Since I have not opened the refrigerant valves, I assume the two lines are isolated from each other.

The red knob was closed . I just closed it with more force and am trying again. I’ve also tightened the adaptor and hose fittings a bit more than max finger tight (visegrip, judiciously).

Could my cheap gauge set be defective/leaky in some way? I don’t want to be the workman who suspects his tools rather than his own lack of qualifications, but if this current attempt yields the same result in both linesets, then . . . I’m running out of ideas.