The power of your compressor is given by P = V x I = 12 x 30 = 360 W. This sounds about right.
It sounds as though your compressor is badly made and that the pressure switch is not adequate for the job.
You could try to modify like this.
Figure 1. Relay control of compressor motor.
Rewire the unit as shown.
- Use a 12 V relay rated for > 40 A. Your local car parts shop should have something suitable.
- When the pressure is low the switch will close and energise the relay.
- The relay will power the motor.
- When the pressure is high the pressure switch will open and the relay will turn off. This will turn off the motor.
- The pressure switch will run cool because there is only the relay coil current passing through it.
- Use heavy gauge wire for the motor contacts. The relay coil can be light gauge.
Figure 2. 12 V relay found by OP. Terminal numbers used on Figure 1.