Generally speaking, Air con is disabled by ECU at start up and Wide Open Throttle, via a relay.

Also as said revs are usually increased in preparation for the extra load.

Also ECU will bring on Condenser / Rad fan /s and leave them/ it on after switch off to cool the Condenser.

I found that on my Focus the ECU also disables Front / rear heated screens and heater and A /C at start up.

I just traced the wiring back to a relay and put an ordinary ignition feed to it.

I'm not using A/C but wanted all other heating.
My V8 ECU has A/c signals that I could have used.

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