[RB777]

The Fitech efi system offers a black wire that allows for a programmable bump in rpm’s with compressor activation ...it also offers a yellow wire with a programmable electric fan activation at a pre-set coolant temperature...

I have been using the yellow wire to trigger a fan relay and it works great. Now I’m trying to get the black wire to do its job but I need an A/C ground and I am not sure where to find one. I see that the A/C binary switch can be replaced with a trinary that will send a ground signal but it makes sense that I should also tie it into the fan relay to activate the fan as well...

If I just tie the grounds together I’m afraid that I will bump my rpm’s upward every time the electric fan comes on...which would be ok but no ideal.

Has anyone recently tackled this idea ...?

 

[OZOZ]

I know asking on a vintage Mustang forum about fuel injection and electric fans is kind a long shot …

After doing some more research I see where the trinary A/C switch would definitely get me a ground wire that’s activated by the compressor kicking in.

Sharing that ground wire with the fan may require some sort of in line diode…

 

[a793aa]

Is your engine's RPM at idle getting bogged down excessively when the A/C clutch cycles to ON?

 

[OZOZ]

Yeah… if I’m at idle and the compressor kicks in it will either stall outright or the rpm’s will pull down and it will barely recover..
I kind of blame my cam for the uneven idle.

** and that’s in neutral.
I have a T5…

 

[JohnnyK]

So do you want it to bump up whenever the compressor is engaged?
You can use a relay to give yourself a ground (instead of 12v) if I'm understanding your issue correctly. I had to do that with my PF4.
Just splice into the compressor 12V to the relay (Pin 86) and ground 85, so the compressor is activating the relay coil. Then run a ground to 87 and 30 to your black wire, so that when the relay closes, Pin 30 gets a ground. (IF I understand your problem).

 

[Woodchuck]

The Fitech efi system offers a black wire that allows for a programmable bump in rpm’s with compressor activation ...it also offers a yellow wire with a programmable electric fan activation at a pre-set coolant temperature...

I have been using the yellow wire to trigger a fan relay and it works great. Now I’m trying to get the black wire to do its job but I need an A/C ground and I am not sure where to find one. I see that the A/C binary switch can be replaced with a trinary that will send a ground signal but it makes sense that I should also tie it into the fan relay to activate the fan as well...

If I just tie the grounds together I’m afraid that I will bump my rpm’s upward every time the electric fan comes on...which would be ok but no ideal.

Has anyone recently tackled this idea ...?

Since the compressor clutch is engaged by sending power to it you can add a power-switched Bosch-type relay to its circuit that will give your FiTech system a ground signal. You'd wire it like so...

 

[a793aa]

Since the compressor clutch is engaged by sending power to it you can add a power-switched Bosch-type relay to its circuit that will give your FiTech system a ground signal. You'd wire it like so...
View attachment 863148

Interesting. The A/C clutch +POS signal that triggers a A/C ground signal.