The way you test ground is to identify the pin the computer controls (two have 12 volts - not that one, one goes to the fan or compressor, not that one - leaving just one pin. The relay either has 30,87,85 or 86 marked next to the pins or 1,2,3,5. It will be 1 or 2 OR 85 or 86.
Slide a piece of wire into the pin socket and install the relay, use the meter between that wire and the POSITIVE post of the battery. If you see 12 volts the pin is grounded by the computer - 0 volts, the ground went away.
So you never tried bypassing the condenser fan relay to see if the fan will now run all the time? Try that.
Look for any loose or burnt pins on the relays, fuses, wire connectors for the fan and compressor and the pressure switch.
Let me know what happens if you force the fans on and run the compressor with a full charge in the system. Watch the pressures, if you see 350+ stop other wise let it run and watch the low side, it should be 22 psi up to 45 psi if the compressor is running and the fans are running.