im working on cleaning up more of the wiring in my eng bay. im running a FAST efi system and both of my fans are now controlled by the FAST ecm and i was thinking i could eliminate that plug unless that plug is needed to complete the AC circuit.

basically, no rad fan signal, no AC due to "lack of cooling".

 

If it is the switch on the passenger side high pressure line, it tells the ECM that the A/C pressure is high. And enables the secondary fan relay. It goes to the ECM so that it knows to run the primary fan.

Hopefully the FAST system has a way to know that the A/C system is active.

RBob.

 

It does. It ties into the factory AC harness to bring up the RPMs when the AC is on.

If I can eliminate that piece of harness without issue then I will. None of my factory ECM harness exist now.

Other than the AC everything works correctly, speedo, tach, oil, temp, batt, cruz.

Sent from my electronic leash.

 

And turns on the fans?

RBob.

 

Right now I have both fans controlled by the FAST system as a primary pair so I'm not sure. Never had the AC working. Getting this ironed out now as I'm going to yank all of the harness back out now that everything has a home and tidy it up. Sent from my electronic leash.

 

To start, you need a fourth Gen 3-wire pressure sensor switch (AC Delco # 15-5742, GM # 22664328). It lets the ECM know the AC is on:





You will need:
1. AC request circuit - 12v into the PCM when you want the AC on.
2. AC relay control - ground signal from the PCM to the AC relay
when the PCM tells the AC relay to activate.
3. AC clutch status - 12v into the PCM from the AC compressor
clutch. This is just a verification circuit to the
PCM to let it know the compressor is on.
4. AC pressure sensor - This is the 3 wire sensor that needs to be
installed into your high side AC lines. If needed, extend this sensor to your high side sensor port.

Not familiar with how FAST deals with these, or the wiring (or non-existence of) of your car.