Quick background...

Bought car in the winter, a/c didn't work, PO converted to R134, didn't care then, it's about to get VERY hot in AZ, I care now, trying to fix, read below...

No pressure on the low side, I hook up venturi style vacuum pump and manifold to see if there is a leak before I attempt to start replacing everything. My air compressor is kind of lame and I can only get about 19" vacuum on the system however it has been holding that for 4 hours now without a loss. Am I safe in assuming that I don't have a leak? I know you need to pull 29" for hours in order to boil off the water before refilling, but at this point I'm just checking the mechanics.

I also know I'll need to get a new dryer and might as well replace the expansion valve but I'd like to not have to replace the compressor or track down mystery leaks once I do recharge.