How long should it take for system to draw in refrigerant?

[GMBDguy]

Assuming a completely vacuumed system. About how long should it take to draw in a 12oz can?

Last 2 times I have tried it seems to take quite a while. I did not time it but it seems to take 20-30 minutes.

[tbirdtbird]

That would not be unusual

[JohnHere]

A few questions: Did you achieve a vacuum of 29.9 inHg or thereabouts depending on your elevation? The higher the elevation, the lower the achievable vacuum level.

Is your vacuum pump in good condition (fresh vacuum-pump oil of the correct type, all connections air-tight)?

Are you charging the system via an unimpeded path: The low-side hand-wheel on the Manifold Gauge Set (MGS) fully open and the thumb-wheel at the service port also fully open? Of course, the high-side MGS hand-wheel must remain fully closed during charging.

Are your hoses connected to the MGS correctly? Some hoses have internal check valves that impede flow if they're reverse-installed.

When attempting to charge it, do you have the system turned on so that the compressor engages as soon as the minimum pressures are reached, thus drawing-in the refrigerant?

Are you using the correct can-tap valve, and is it fully open? The newer self-sealing small cans take a different type valve than the older piercing-style cans.

Are you charging with the refrigerant can upright and keeping it as warm as practical (not hot)?