Super COOL (sorry) cooling fan control discovery!

[gmtech16450yz]

(Disclaimer- This may be old news to some, but I've never heard it mentioned or tried. I'm pretty sure this will be a new discovery for most.)


Ok so I saw some recent discussion about the fan logic on Gen 4 cars and how you can't control the fans below 192* unless you use a custom OS. So I revisited my fan settings on my LSA Sky to see if I could tweak them a little better. I didn't like the idea of NO fans until 195.8* so I've been running my fans on low speed pretty much all the time. Kinda cr@ppy in the winter when I could drive back and forth from work and never really need them on.

So here's when the light went off over my head! A/C pressure! Refrigerant pressures run close to air temps, so I looked at the A/C pressure table in my E67 to see what pressures it had control over. The lowest cells are 600, 725, 850, 975, 1,000 and 1,225 kPa. Those convert to 87, 105, 141, 160 and 178 PSI. So I set up that table so the low speed fan would turn on at 141* and turn off at 105*. Drove it a few times and the logs confirm the low speed fan is turning on at ~136psi and off at ~103*! (A/C on or off, it doesn't matter. Obviously if the A/C compressor was on the pressures would be way higher but at that point you'd want the fan on anyway.)

So this is why I think this is cool... My cooling system is efficient enough that even on a very hot day, temps tend to stay below 195* which is the lowest temp that I would be able to control the fan. But what about when the coolant temp is ok (below ~190), but the under hood temps are really high? THAT'S when the A/C pressure is a useful input. It will show you what the temps under the hood and around the radiator/condensor are. (Log them and you'll be surprised at how accurate they are in giving you an idea of temps.) So now I can have my coolant fans stay OFF under most conditions when coolant AND underhood temps are low or ok. But not only will the fans come on at 195*, they will also come on if the A/C pressure gets up to 136psi, which is roughly 120* IAT temps. That's when you'd really want the fans to come on, especially when you have fans on a supercharger heat exchanger that are tied to coolant fan operation like I do.

Here's one of the scenarios I've already run into... 90* day, cruising down the freeway, coolant temp is nice and low and so is underhood temp. Come off the freeway and start doing some slower, curvy road driving. Coolant temp is still fine, but underhood temps are getting hotter. A/C pressure turns the fans on even though coolant temps are below 195*. Everything runs a little cooler with the fans running in that situation. Get back on the freeway and as the underhood temps/ A/C pressure goes back down, the coolant fan turns off. Fans aren't needed in that situation so there's really no need to be running them. PERFECT! Try it out guys and see if it works and helps in your particular situations. It's a "cool" alternative to not having ECT control of the fans below 195* without having to go to the custom OS. I'll take a couple screen shots of my fan settings so you guys can visually see what I did. Enjoy!

[DrkPhx]

The lower ECT fan values are there, you just need access to them. The other guys has an operating patch (not a custom OS) you can apply to get access and modify them.

[Chris@HPTuners]

The lower ECT fan values are there, you just need access to them. The other guys has an operating patch (not a custom OS) you can apply to get access and modify them.

they are not hidden, the axis lower limit is hardcoded in the ECM, hence the patch. Both solutions change the same thing.

[gmtech16450yz]

they are not hidden, the axis lower limit is hardcoded in the ECM, hence the patch. Both solutions change the same thing.

Thanks Chris!

This isn't totally about the coolant temp/fan control table, it's about an ADDITIONAL way of controlling the fans that might not be common knowledge. The A/C pressure table is nothing new, it's obviously been available to modify for a long time. I never thought about two factors concerning that table though. One is the fact that it uses that table whether the HVAC is on or off, and the other being that the lowest cells go down to 87psi. That 87psi is low enough to be a factor with the compressor on or off. And the fact that refrigerant pressures are close to temps in Fahrenheit means that table can essentially be used as an ambient air temp trigger for fan control. That's cool!

So the way I'm using the A/C pressure table is not as a replacement for the coolant temp table, but an addition to it.

[JBZ]

im sure that you have the two spreadsheets that are in a link in the Gen 4 sticky but just had to say that I took a look at this, ended up implementing what you did here because I found that my fans were not doing what was commanded. I must have played around with the 2 spreadsheets for an hour trying to get them to line up and it looks like you have done your homework. im pretty sure the vowners members would be pretty interested in this if you haven't posted it over there already.

so I tried to keep the fan desired vs current state and could not for the life of me get the temps I was looking for, so I tried yours and what do you know they lined up perfectly. I downloaded them in 2 days ago and I have to say it is keeping the coolant temps 10 degs F cooler on average in the afternoon drive home. in the morning when its cooler out side it is negligible, but when its matters when it warmer it is keeping the ECT's between 180 and 190 during stop and go traffic down here in Houston, it has been about 90 outside both days.

so what would be any (if any at all) downside to this? running the fans too often, cycling too often potentially stressing the fan motor? well at least the second fan anyways, the way my tune had previously had the fan 1 come on always and never turn off. are my ECT's too low, I know there is much debate on engine and oil temps?

also just to note, I didn't see much of a difference with IAT2 temps (maybe a degree or 2) but I did notice that when I did get on it at all after traffic that my recovery rates were better... obviously because both fans were running.

this is good stuff John keep it coming.

[Michael_D]

I just stole your AC table settings for a freind's Vette who is havng trouble with his ECT's in 115 deg weather.

Loved your Sky build video. Some very impressive fabrication skill there (I am a milright by trade). I'll also pretty jelous of your shop. Damn, you have your own Bridgeport... Where's the engine lathe with VFD and water jet?

[BigMike42]

This is very COOL.

[JBZ]

It has been hovering in the high 90s over the last week and my ambient has been right at or around 100 and sitting in traffic the highest temp i have seen is 198 now. But typically has been around 190. Getting as low as 180 cruising at fwy speeds. I am liking these settings.

I made mention that i didnt see any difference in my IAT2 temps but it actually has been pretty impressive. When the temps are anything below 90f outside i typically have a delta T of 20f and that drops as the temps go up. The highest IAT 2 i have seen in traffic to date since changing to this fan scheme is 117f but most of these 95+ days its been right at 115 in stop and go and 109f cruising. That of course is dropping my delta T a few degrees.

Impressive

[gmtech16450yz]

Thanks guys!

Yeah, I've been running these settings for a few months now, I really like it. The biggest difference I like isn't even when the fan runs, it's when it doesn't run. Before I pretty much ran it on low speed all the time until the temps got above 199, then it would be on high. Kinda stupid running the fan through the winter when it really didn't need it. So now my fans don't come on until either the coolant temp is high enough, OR the underhood temps are high enough. That's what's awesome, the coolant temp can be below the fan turn on point but the underhood temps might be hot enough that it needs the fan on. There are a LOT of situations where it's the A/C pressure signal that's turning on my fans before the coolant temp would have. I like it!

Thanks Michael, I absolutely LOVE that Bridgeport! A friend of mine that buys and sells heavy equipment like that picked it out for me. It had very low hours but just needed to be cleaned up and gone through. The chrome ways are still like new. I took the entire mill apart, replaced all the bearings and belts, polished all the aluminum and painted it gloss black instead of boring grey. I have learned SO much working with that machine, there is so little that one of those Bridgeports can't do. I don't have a lathe mostly because i don't have enough room for one, but I have things that make lathe-type work possible on the mill. One of the best pieces I bought was a huge rotary table. With a little thinking outside of the box I've gotten by ok without a lathe. A water jet would sure be nice though!

And yeah, my shop is one of my "happy" places. I built it myself from the ground up and it does pretty much everything I need it to do. It is a small shop/garage compared to others in most any other part of the country, but that's because we're in the SF Bay Area and lots are small. I have it packed full of a ton of tools and equipment though! It sure is nice having just about everything you need to build or work on most anything you want.

[GHuggins]

I for one love that car A LOT of skill and time went into that one...

[BigMike42]

Gonna try this this week when I swap my mr gasket 180 in. I cannot keep my car under 210 with the stock thermostat even with the fans on full blast.

[15PSI]

I normally don't view the GM stuff as I am a Coyote guy, but while searching for IAT2 temps and such, I came upon this. Unbelievable. I have designed, fabricated and built race cars and race bikes for practically my entire life. But... I don't think I have ever come across such a completely nuts home-build such as this. I watched the video, all 18+ minutes of it and was smiling ear to ear. What a great job. I absolutely love that car.