Help locating A/C trigger wire

[RYU]

Might someone be able to tell me which signal wire coming out of the ECU harness is the A/C compressor trigger wire? Wire color and pin location would be huge help.

I need to tell my stand alone ECU to compensate idle conditions when the AC is on. Never needed this before but ITBs are a bit finicky and I'd like to compensate for this to have OEM like idle.

Thanks in advance!

 

[Old Guy]

I am assuming that you are looking for the 'request signal' from the CCU to the ECU indicating that the compressor should be engaged (and apply idle up). The arrangement is slightly confusing; but, as far as I can tell the CCU request signal comes out of the Rad Fan Control module (CCU to Fan Control to ECU). On 1991 cars this signal comes in on terminal C3 which should be a Blu/Blk wire. On the version of the 1991 service manual that I have access to there is some conflicting (or at least confusing) guidance on exactly the position of C3 in the plug terminal. I will let you sort that out. Note that Honda reassigned the ECU pins on later cars. I expect that might have occurred with the OBDII which required more pins; but, I will let you sort that out if you have a later vintage car.

Be aware that as far as I can tell the request signal is a pull down from the fan control unit. The ECU has an internal pull up resistor and C3 would float at around 12 volts until it is pulled to ground by the fan control unit requesting compressor operation.

The compressor clutch is controlled by the OEM ECU. If you still have your compressor clutch controlled by the ECU you may already have the AC request signal wired into your ECU.