Found it. I lost the original photo with a drive failure years ago. Damn, over 15 years ago I posted that.

https://www.autoacforum.com/messageview.cfm?catid=20&threadid=12050

Last photo

It actually squeaked down to 800 a couple of times in other tests with a little more oil.

Somewhere on the old site I posted a picture of an FS6 that would pump down to 800 microns on the suction side - with the discharge open to atmosphere. I was only turning that FS6 about 250 rpm too. I would trust the York if it was in good shape. But a tired hermetic from a discarded refrigerator is...

Fast Forward to the 11 minute mark to see the water boil off.

sure shows the shortcoming of scrap refrigerator parts as vacuum pumps too!

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Contact Aeroquip and find out what the annual permissible leak rate is for that fitting. Everything leaks a little. You are losing a pound in 3 years across 8 fittings and several feet of hose. Commercial stationary comfort refrigeration is allowed to leak 10% of the total charge per year by the EPA...

An ounce or two of refrigerant should give you plenty of pressure for a leak test. No need to fully charge the system.

Manifold valve leaks and service hose / connection leaks happen occasionally. More common on rental / loaner units...

You can place the LPCO in series with the HPCO when installed in the High side of the loop.

This will inhibit compressor operation below about 25f ambient, and when the system is completely empty - static pressure below 30 psi.

A little protection from the worst events.

Side can tap is the only way to go. Always works, any size can.

Year / Make / Model of your car would help us with a diagnosis.

Low side service connector not depressing the Schrader valve. You have charged the service hose.

Try depressing the coupler a little bit to see if your low side gauge drops.

A blockage at the TXV would result in a reduced low side pressure as the refrigerant stacked up in the receiver dryer. If the TXV was restricted you should see calm liquid in the sight glass. The receiver is designed to deliver liquid to the TXV. If the flow is reversed it does a lousy job of that. ...

Receiver / Dryer installed with flow in the right direction?