Hi,

I was using an Evo 7/8 ECU in my Galant E30 FWD turbo with AC but without the load request signal - it idled OK and with some ignition timing tweaks it regained stable idle rpm pretty quick after the AC switched on or off, but it would be nice to have the ECU know about the AC status - plus i'm rewiring everything engine related in the "new" Galant VR4 anyways...

So is the load request signal from the A/C ECU to engine ECU only a simple GND or Vcc Signal or pwm/data?

 

+12V signal. But for evo7/8 ecu it's actually "a/c on request" signal because it drives a/c compressor relay by itself.

 

So from what pin/signal the ECU determines if the AC is on/off?

Pressure switch (pin 45) and compressor-relay (pin 8) were already connected to the ECU but I never got an "AC on" status from the ECU (evoscan or MUT3 tester), so I was assuming that the connection on pin 24 is used for feedback from the AC ECU to determine the actual status of the AC.

I'm commenting my way through an 9653 disassembly since a few months (which i'm happy to share and discuss some findings as soon as its "done"/presentable, as some comments may contain strong language ), but haven't looked deeper into the AC routines yet plus its also still missing large parts of the address->uC-Pin->ECU-Pin mapping.

As said: the car idles good (better than any of the old eeprom ECUs i've used before) and also regains stable rpm after the AC switches on/off quite fast, but as I'm refurbishing the whole engine wiring anyways it would be a "very nice to have"...

 

I would guess the pressure switch on pin 45 is the only way the ECU can tell if the compressor is "on". From the wiring diagram it looks like pin 24 tells the ECU when you push the A/C button on the control unit.

 

Sorry to bring this back from the dead. I'm going through the same issues as the OP. Swapping an EVO 8 ECU into my 2g GSX. Should pin 24 be used somehow? I noticed that pin 42 (AC Pressure Switch) from the 2g ecu was not used. Attached is a scan of the pinout I used to convert over.