Paul, The solenoid is 24V but the compressor has a 12V motor. Same thing just need 10A at 12V but thats exactly what Ive now done. Got a PIC12C508A to get the signal from the RX and convert it to a PWM output through a MOSFET to the compressor motor. It also has a auto zero upon powerup for the RC input and a softstart function to reduce EMI from the motor. The pressure switch is then connected through an LED to another input of the PIC to light when upto pressure.

The PWM freq is only 2.08kHz but with 32 steps (only first 16 used upto 50% duty cycle) gives a smooth startup. This gives me 7uS for the PWM rountine and 8uS inbetween to read the Rx input with 16uS resolution. Now that was a challenge.

It seems to work ok so far.