As you know, the AC doesn't work with the Apexi pFC in certain vehicles so Chuck Westbrook came up with a bypass by connecting two pins of the harness together. Unfortunately, the AC is always on if the A/C switch and the fan switch in the dash are on. Chuck went with a pressure sensitive switch to turn off the AC under boost.

I'm leery of having a boost leak at 7500 rpm and possibly ruining the AC compressor. My solution is to regulate the AC with engine speed.

I bought an rpm switch from racerpartswholesale.com for $50.00.

The switch is designed to turn a light on at a selected rpm. I plan to have Chuck Westbrook AC fix normally on with the rpm switch disconnecting the connection whenever the rpm exceeds 4000rpm with a relay.

My question is: Is there a pin in the computer harness that will let me tap into an rpm signal for this switch?

Has anyone tapped into the rpm switch to control other functions?

 

If you place the switch under the hood and tap into the wires from the AC pressure switch for the relay output, you can get you RPM signal from the ignitor connector wire for the leading coil. That is where I have my tach light connected to. If mounted inside the car, get the same wire where it comes out of the ECU. This gives two sparks per rev like a coil output for a 4 cylinder boinger.

 

You can get a tach signal from the Diagnostic box in the engine bay. Just look for the IG- pin.

Also, there is an RPM wire going into the ECU. I have not verified if it's the same signal as that at the Diagnostic box, but it's the wire Apexi uses for their rev/speed meter and other devices that monitor RPM. It's wire 2B, in the 12 pin connector, yellow-blue.

-Scott