Carbed sbc 400. My R4 compressor started making noise so I bought a Sanden "Style" a/c compressor. I know my mistake. Any way it works good. Blows cold air 40* at idle. When I have the idle set where I want it idling in D and then turn the a/c on the compressor pulls the rpm down to much. So I added a idle stop solenoid. But when I cruise through town at 30 mph with a/c on and idle stop solenoid activated I cruise right along with out touching the gas pedal. I don't like that. My question is does an actual Sanden a/c compressor pull the rpms down much? How much? Do you still need an idle stop solenoid? Can you use the Sanden a/c with out a idle stop solenoid?

 

Depends on LOTS of things. Starting with your definition of "much".

Depends on LOTS of things. Not least, the tuning on the engine. A carb needs not to be leaned out to the absolute edge of disaster for example. The typical Holley EFFFFF-up of the power valve at "half of idle vacuum" is almost guaranteed to lead to this, for example.

A compressor - ANY brand - can't miracle up the power to compress refrigerant out of nowhere. It HAS TO draw power from the engine. The engine responds by slowing down, if it can't deliver the power. Not that hard to figure out. It's not that much different, big picture, from getting an auto trans car to idle right and not die when you drop it into gear. Many of the same tuning techniques that work well for automatics, work equally well at working for compressor load. Or power steering load (dying when turning into a parking place for example). Or anything else that puts load onto the engine and it has to deal with while idling.

In general, it's a TUNING problem, not a "Sanden" problem, or an "AC" problem. It's all about engine tuning.

I'm assuming you've been all the way through the Holley Tuning sticky at the top of the carb forum, in order as described and not skipping any steps or taking any out of order, and all of that is now PERFECT?

 

I will add to what Sofa said above by saying most idle issues are ignition timing issues. You want as much initial timing as the combination will tolerate and vacuum advance on the manifold vacuum port. A SBC even a stock one generally idles best around 25-30° of idle timing. If you have the vacuum advance on ported vacuum and use an idle kick up solenoid it can make the idle very quirky. You should not need much additional throttle opening to offset for the ac compressor load. IIRC from years ago the factory adjustment procedure was to unhook the clutch, energize the solenoid and add 50 rpm to the base idle. Then plug the clutch in again and you were good to go. The idea was the solenoid would keep the idle rpm the same both with and without a/c on by compensating for the ac load. The solenoid is also too weak to kick the throttle open, it only holds the throttle more open once the throttle is opened above idle and the ac is on. So when the solenoid is adjusted one needs to blip the throttle open, let the solenoid fully extend, then set the idle speed with the solenoid energized and fully extended.

 

I went by the Holley manual when I set it up. Of course I could be off but I'll check it again.

I have my vacuum advance hooked up to port vacuum because that's what the distributor instructions said. I've had my idle timing from 8 to 14 btdc. Looks like there are some things to try. Thank you. More input is always welcome.

 

Yeah that explains why it doesn't run right. Doesn't work, never has, never will. No idea why they still publish that CRAP. Was written in a different day and time when there was ALOT less knowledge in the world at large than there is now.

https://www.thirdgen.org/forums/carb...ey-tuning.html

It's a bit incoherent. I didn't exactly "write" it, rather, one of the mods back then, cut & pasted abuncha the stuff I had repeated OVER AND OVER AND OVER AND OVER into a single post I guess because he got tired of seeing me post the same thing OVER AND OVER AND OVER AND OVER again. He did a pretty good job overall though.

 

Another item to address would be to confirm the TCC on the TH700-R4 does not engage below a moderate speed, like 40 MPH plus. My '86 TPI did that as stock, and the lockup engaged at 28 MPH. With the AC on and driving a 2.77 Borg axle, it would not run in 30MPH posted zones. The TCC was bumped to 41 MPH and it resolved all of that.

 

Yes the TCC does lock up around 30. If under 40 the engine chugs so I shift in to D. a/c on or off doesn't matter. How do I bump up the lock up to 40?