HEVAC to LO...In the first minute or two after ignition (and before the service book comes on) is the clutch plate magnetic (ie touch it (safely) with a spanner, to see)..If yes, then the clutch is contaminated or needs re-gapping. If no - engine off - unplug the round connector at the compressor - put 12 volts (or a regular 9v battery) across the terminals - does the clutch a. magnetise and/ or b. engage ? If you have a clamp meter, the clutch will draw about 3A when engaged ( i think i measured that using the 9v battery). If no, then compressor (or at least, the clutch) may be at fault.
If yes, then get the nano and check that HEVAC is issuing a/c request to the ECM (12v line, but active low), and that ECM is returning an a/c grant to the HEVAC (5v line but active low) - without those the HEVAC will not send 12v to the clutch (or relay, if you have a relay harness fitted). It's also pretty quick to do a continuity check from the RH footwell to the compressor (if you have no relay harness fitted) which would help eliminate i. low/ no gas ii. a dodgy pressure switch and iii a line break.
Next step wd be to pull the HEVAC ECU and start testing pins, but if you have a nano and trust that then you may be able to avoid that but if/ when you do pull it, note the serial of the ECU fitted.
