18031 Fan desired % VS AC pressure recommended settings
Does anyone have any advice on what range of values to use in the 18031 Fan desired % VS AC pressure table? I'm talking at what pressure should I enter the first/lowest speed (e.g. Perhaps it's 0% for all the pressures below 130 psi and the cell for 141psi is the first entry at 10%). Then ramp them up in each cell through the rest of the table, perhaps by the time I get to the cell for 359 psi is the 90% value and all cells after that are 90% also.
Engine is an LS3 with e38 and I'm doing PWM Electric on a single fan.
I'm trying to drive my radiator fan via pwm and want to do my best with using lower/slower speeds if I can get away with it, instead of just a hard brute force "half speed" or "full speed" setup whenever fan is needed for AC. It would be great if, for example, the fan I'm using is large enough to only ever need to have it running around the 10-30% level for anything that the AC ever requires. No point blasting away on the fan at higher speeds if both the engine temps are under control and the AC doesn't truly need any more airflow. Rad fans can certainly be annoying with noise at times.
I guess my question is over what range of high side pressures should you generally be running a fan and at what speeds in order to run the AC system well?
The e38 I have came programmed for relay driven fans, not using pwm. And the fan desired % VS AC pressure was 0% all the way through to 195 psi cell, then 50% in 213 psi cell, then 90% in 232 psi cell and all the others through to the end. Therefore I can't really use the old "just stick to whatever it came with by default" method here.
Just like any other aspect of tuning, you need to collect some data - in this case it'd be good to know the relationship of fan speed vs high side pressure vs discharge temp to know if/which direction it needs to be adjusted.
Because this is my first adventure in this LS swap arena, this is why I was hoping to find perhaps a table for this fan speed VS pressure that had largely worked for someone else before. Perhaps I could use that as a starting point, then go from there in fine tuning, logging temps etc and fine tuning as needed.
I know all our systems/installs/applications are different, so it's like asking how long is a piece of string, however with the very hard on/off settings which my table currently has seems to be quite illogical and not relevant to what I'm doing.
In my mind, getting something of a more progressive slope looking table and fine tuning it from there is much more logical than starting with this silly cliff looking slope and trying to fine tune from that. Problem is, just finding that example ski jump style table.
I would be confident that someone who has a C6/7 or Camaro or SS/Caprice/Commodore should surely already be using some kind of relevant table with settings, so I was keeping my fingers crossed someone might have responded and said something like "here's what mine looks like....". If I started to gain some confidence in what "normal" looks like I would then probably have some better understanding as to what I should be looking at, seeing etc.
P.s. If I go to the tune repository, can I download some tune files from various similar vehicles and check out what they have done without consuming a credit? Or does just opening a tune file consume a credit?
If I can freely open other tune files to have a sneaky look at their examples then basically I could find this out myself.
I basically answered my own question. I downloaded 60 tunes from the repository for vehicles I thought would be somewhat similar to see what the tables looked like. Generally speaking they were largely similar, but also had their differences...
For Commodore, across 6.0 and 6.2 litre engines and for all years through to 17 when they canned it the table is the same. I find this silly, annoying, especially for the later years like VF when they clearly had pwm fan control and yet still decided to manage the AC demand with a simple 25% 50/ 90% speed strategy. (I'm in Australia so Commodore is closest to my understanding/experience).
Camaro/SS settings also look to be using a 25/50/90 strategy but interestingly enough the table has shifted a bit to the left. It looks like the fan starts a little earlier and hits 50 and 90 much earlier in the mix. I wonder why this is? Because of different market than Australia, temperature conditions? Or perhaps different AC gas or charge pressures are used there?
Onto Corvette and I noticed a difference in the pre and post 16 tables. I know close to nothing about Corvettes so I'm sure someone can comment on why there seemed to be quite a difference when 2016 came along.
In all these instances (except for Commodore) I looked at the 6.2 litre tunes only. I only accepted looking at the 6.0 tunes on commodore because there weren't a lot of the 6.2 tunes to be found.
So what does this mean for me? I'd say I will start with something similar to the 16+ Corvette table. First entry at 6% at 1100kpi and then smooth ramp up to 90% at 2350kpi. Is this correct, a good idea etc? Who knows, but I gotta start somewhere so that's where I'm gonna start!
How the AC responds to fan speed/airflow is entirely dependent on how good the condenser is at dumping heat, and how much heat there is to dump. Obviously these are affected by things like condenser size/efficiency and everything that affects the heat load being delivered to the condenser from the cabin. And one fan's "30%" isn't going to be the same amount of airflow and pressure as a different fan's "30%".
On my truck, converted from a viscous fan to variable speed PWM, it works fine with a flat 30% fan speed (below 15% is 'off') from 159psi all the way through 286psi, then jumps to 60% for everything above that. Logs have never shown it above 260psi in normal use. I found that, with my condenser and everything else, that higher fan speed made very little difference in duct temps, at least not enough difference to make the screaming fan noise worth putting up with. On a different vehicle with different AC components in a different environment the results might be totally... different.
Set fan speed to a flat low number. Drive & log & record discharge duct temps. Then do the same with higher fan speeds. See if the extra airflow actually does anything worthwhile or if it's just making noise for nothing.
I'm just going through all this now with an interchiller installation.
After logging I've determined at idle, engine hot my AC pressure is 1250kPa, ambient was around 27degC and very humid. When the fans kick in they drag it down to 1000kPa. Then when cruising on the 110km/h zones I'm still around 1000kPa. In the log shot you can see the fans are still running at 75% when doing 110km/h.
There is no point having fans on when cruising at 110km/h so have since set the table as below to see if they turn off, but when I stop, the AC pressure should rise and they should ramp up to max. Haven't tested this yet but I think you get the idea. The red line is what I want to see the fan do.
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