discomania said:

Same circuit except your circuit assumes the original switch was remote to the compressor, my circuit assumes the switch used to be ON the compressor which the OP also said it was - like the 'assumption' sketch - which is how I think the wiring inside the compressor works, minus pressure sensor, overheat sensor etc. if fitted.

Click to expand...

Aye

skint-as-usual said:

The 12v to the IR receiver and low power relay side I would recommend tying into IGN switched electrics (such that it is not on all of the time).

These may be white IGN unfused
or
Green, from a fuse (say fuel gauge?)

Click to expand...

Good shout.

Did the ebay page give a mA current for the device in 'sleep' mode?

Specification:
This is the self-locking Receiver + Remote Control Kit. When you press the ON key, the relay of receiver board close, LED lights; when you press OFF key, the relay release, LED off.

1 channel Self-locking R Receiver Controller:
Operating voltage: DC 12V
Quiescent current: ≤ 1mA
Pick-up current: ≤ 80mA
Remote control distance: MAX 8 meters
Work status: Self-locking
Size：50*20*20(MM)

Infrared Remote Controller:
Using UPD6122 chip ,NEC encoding format
User code :0x00FFKey value ："ON" Button is 40;"OFF" Button is 19
Battery powered : CR2025
Size：86*40*6(MM)
Note:The receiver board must be equipped with a suite of remote control, it cann't recognize other remote controls.The load capacity of this relay is 250VAC-10A、125VAC-10A、30VDC-10A、28VDC-10A.

Package Included:
1 x Receiver Board
1 x Remote Controller