I thought that you listed 1.5 bar above, which would prevent compressor engagement.

7.5 bar probably isn't enough pressure to do much of anything, and this could be the problem. Be sure to verify the reading on the pushbutton unit with a gauge on the high-side service port.

The resting pressure means very little, unless it is very low. The pressure that you will see depends on the refrigerant temperature alone, as long as there is any liquid in the system.