For my 04 Sierra 1500 5.3L I had to replace the tube assembly with the high and low side ports (and orifice tube in between) because of a stuck, non-serviceable schrader valve on the high side port. I'm doing some work that will require me to open the system up, again, so there's no sense charging the system with R134a (since I know I'll need to replace it in a few weeks). It's cool/cold out, so I see no need to use or engage the AC. As I understand it the compressor should be prevented from engaging by the low pressure sensor in the system, anyway -- which may be relevant as I have climate control (I tend to manually make sure there's no snowflake showing, though). So, is there any reason not to leave the system at -27Hg for the next few weeks? Please advise.