Yes, but don't you think I can jumper those 2 ECU pins and regain full function other than stepper motor control?

Frank

I would expect to regain use of the AC you either jumper them or run a new wire up to the compressor. You will not get idle up from the MS with your firmware.

Yes, I knew that going in and hoped the A/C compressor load would not drop the idle appreciably. Testing it for idle quality is how I found out the compressor didn't work... when I tried to check for idle issues with the A/C on during the first warm spell it didn't work and I realized that there was an ECU connection.

I have the relay installed in the relay board for a FIdle circuit and included the FIdle circuit on the main board plus the trigger wire in the harness to the engine bay.... so if the A/C compressor loads the engine too much at idle, I can add a switched air valve/solenoid of some type to bleed a little more idle air into the mixture.

One of the OE EGR solenoids might work well for that purpose if I can size the orifice correctly.

Frank

Can you rig some bypass air with a lectrovalve, adjusted to a base idle rise with an aquarium air needle valve?

I'm not yet sure if I need it - or if I do, how I'll go about it. Somehow, I'll need to take a trigger voltage from the compressor switch circuit and use it to switch a solenoid valve to provide air behind the throttle plate. I don't see why I couldn't run a bypass from before the throttle plate to the solenoid, then on behind the throttle plate.... trigger the solenoid with the compressor clutch switch.

I might find the FIdle relay circuit in MS useful for some function in the arrangement ..... just don't know yet.... it would depend on how much current one of the solenoid switches would draw.

Frank

GM stuff is full of lectrovalves for engine vac that should work fine. Get one that's NC and opens on power, and tap the compressor clutch circuit for the power. Tune the idle up air amount with the aquarium needle valve. Plumb it from front to back of TB. Air cleaner case to a ported vac tap should work fine. May have a minor lean out effect on a/c'ed idle mixture, but you're rich at idle, anyway, right?

I said "EGR solenoid" earlier, but I meant the purge solenoid valve - located on our trucks just below the purge cannister... an extra one of those should work just fine.

The aquarium valve might work for air flow adjustment..... or I could adapt a carburetor needle and seat into a small box. The best arrangement might be a fixed opening, though - easy enough to make by plugging a vacuum line fitting with epoxy, then drilling the epoxy filling with the correct hole size..... trial and error notwithstanding, it might be an easy fix.

First, I need to get the A/C compressor circuit working, though.

Frank

I'd guess the path thru the ecu is just for a/c on sensing for idle up. There's a hi-lo limit pressure switch in the refrigerant circuit in the a/c. I guarantee the ecu does not turn off the a/c in an overheat. Jumper it.

that's common for alot of vehickes now a days... and a even some of these antiques would cut off compressor when sensing a great load on the engine. I think Isuzu 4 banger does.

I dont think lower idle will be a problem. When I had an open coil in IAC , the idle would drop from 600-400 with A/C on.


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I never use AC because I dont have to...bums can sweat all they want

Right - that function is provided by the engine coolant temperature switch located on the passenger side of the intake manifold water box.

Frank