Idle speed in D ac on hot day

[jetfiremuck]

As title says what are you all setting idle speed in drive ac on (high fan speed). Does the engine vibrate or hunt ? Thanks

[v8volvo]

Idle speed IIRC from book spec is supposed to be around 750-800 with engine warm and trans in neutral?

I have never noticed a major drop in idle speed with trans in gear on the automatic Volvo TD cars when everything is working correctly, maybe a few hundred RPM. AC switched on can drop it a little further. But if yours goes low enough to vibrate and hunt/surge, that says to me that your injection pump may still need further fine-tuning (wrong calibration settings can impede the governor from compensating for load, as it is designed to do up to a certain extent), or the IP may have some worn internal components that show up as the hunting behavior when the fuel and engine are very warm (fuel extra thin). I have seen that once or twice on VW diesels with the similar VE injection pump when they get a lot of miles on them and/or ingested some low quality fuel.

OR the other possibility is maybe it is not a perfect marriage of A/C compressor to engine. I think you said one time previously that this setup is running the Land Rover A/C compressor, correct? If so then it is possible that the compressor is a larger one that puts a heavier load on the engine than would have existed with the stock Volvo one. Or another possibility is that the pulley on the compressor is too small in diameter, if it is designed for a higher revving gas engine that was originally in the truck. A big capacity compressor with a relatively small pulley, idling in gear with heavy electrical load also from a fan turned up high, etc, and you can see how the accessory parasitic drag on the engine may be going outside of the original design envelope and require some creative solutions to make it work smoothly.

I would probably start by trying to play a little more with the injection pump settings or consider having it fully bench-calibrated. A good diesel fuel injection shop can do this, or I believe Tom Bryant also has all the equipment now and is probably much less costly to send to him. This would have the side benefit of probably making the engine run stronger and cleaner all across the rev range.

Then if that doesn't bring you the right improvements, you may want to think about changes to the compressor setup like trying a Volvo compressor, and/or continuing with the Rover compressor but building some kind of throttle kicker system to boost the idle when the compressor is energized. I think you had been considering something like that before. Probably wouldn't be too hard to do.

I for one would still very much like to see some pictures or video of your installation some day and hear more details of how it is bolted together. A D24T powered Land Rover is a daydream project for me and probably plenty of others here.