EFI AC

[mashud46]

84 H/O, EFI swapped and kept AC. Removed the ECM harness because it is no longer used. Everything works as it should, however I am still searching for a place to tap into my "Ground Trigger Input" for the AC through the EFI. Basically, I need a wire that is grounded only with the AC compressor on to give the EFI a Idle kick and turn the engine fan on when the compressor is on. Anybody Have any ideas?

 

[81cutlass]

What EFI system are you running?

Keeping the stock R4 compressor or something aftermarket or newer GM OEM?

The mix of AC pump type and EFI system has a big impact.

 

[mashud46]

What EFI system are you running?

Keeping the stock R4 compressor or something aftermarket or newer GM OEM?

The mix of AC pump type and EFI system has a big impact.

Holley sniper. New GM style compressor. Everything works I just need a ground only when compressor is on wire.

 

[UC645]

Holley sniper. New GM style compressor. Everything works I just need a ground only when compressor is on wire.

You could use your trigger wire from the Holley to piggyback another external relay to supply ground like so:

Convert a Positive Output to a Negative Output Relay Wiring Diagram

www.the12volt.com

 

[383_StealthRam]

The Sniper EFI needs to see a neg (-) ground input as you noted for it's AC ON, but the control head in the dash (I'm pretty sure) outputs a 12v (+) on a green wire, which in turn signals the ECM to turn on the compressor via the compressor control relay. Have a look at the diagram posted by 69hurstolds here to see the typical diagram. Note the V8 & V6 are slightly different depending on what your car originally came with.

So, if you had the original ECM still wired up into the system, you could use the BROWN wire circuit 449 that grounds the A/C compressor control relay but since you removed all that, you're only going to have that 12v + signal from the control head when you turn on the AC.

You'll have to use a relay wired up to use that 12v + from the control head to turn on and provide the GROUND for the Sniper AC on signal. Here's a simple diagram that might work for you...

 

[383_StealthRam]

You could use your trigger wire from the Holley to piggyback another external relay to supply ground like so:

Convert a Positive Output to a Negative Output Relay Wiring Diagram

www.the12volt.com

Excellent! I figured by the time I found an existing diagram with all the detail, I'd just draw one up on Visio quick 👍

Great minds !!