AC compressor / clutch '99 E430 W210
 

My AC compressor is not engaging even though the "EC" light stays off when the button is pushed. I ran the diagnostics, which indicates 0 refrig pressure.

What's my next step? I want to verify the compressor and clutch are good, which I do on other cars by jumpering the low pressure switch for a second.

Next, assuming I have an R134 leak, I want to recharge and look for the leak.
Can I recharge with a non-running compressor?