[kuehl]

If this is R12 or R134a, at 70F you would prefer to see around 160 'ish' on your high.
Again, looking at a bogey, if R12 was 33.5 then with R134a should be about 28 oz by weight. You got 18? You are severely undercharged.

The 50 low is baffling, but for the moment.

I would not blame the compressor just yet. But, did it come in a Denso box? New?

Will operating this system with an undercharge hurt things. Yes, possibly the compressor over time. Compressors need a reasonable amount of refrigerant flow to stay lubricated; the refrigerant carries the refrigerant oil through the system.

Side note: On testing for leaks, pulling a vacuum down to 30" is just a test for gross leaks (big leaks). Your system can run up to 250 psi easily on a 100F day.
30" of mercury is equal to 14.7 psi. The best 'testing' is with an electronic leak detector. Next best is dye and a black light however limited to what you can see.