What are the pressures reading when you are trying to charge it? That will be most telling. It will only "draw" more in if the low side is below the static pressure of what is in the can. Tell us what it reads when the compressor is running and both valves on your gauges are shut, then open the low side valve and note if the low side gauge increases any.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz