AC compressor tech questions

[Murray_Calavera]

Hi all,

I'm wanting to have my AC run during track events, however the stock Haltech settings don't really allow for that. (base map settings, AC turns off over 75% throttle and/or over 4500 RPM with a 4 second hysteresis)

I have a suspicion that the Haltech settings are setup that way using the logic that, if the driver is over 75% throttle or over 4500 RPM, surely they want all of the power available so kill the AC to reduce the load on the engine. 

Before I just set it to run all the time regardless of throttle/RPM, does anyone know if the AC compressor can be over revved or if there is anything else I should be concerned about?

 

[Kinkstaah]

An AC compressor is not actually running all the time. Most OEMs will actually avoid the AC from 'kicking' on when you are under heavy load scenarios. The Haltech is mirroring this behaviour by default.

I don't know the RPM limits of the AC compressor but I'd be damn suprised if it only hits its max compressor ability at 7000 RPM, because that is NOT a sacrifice most people would make when it comes to using Aircon, as most of the times you want aircon you are going to be in areas of the map under 6999RPM.

[Chopstick Tuner]

Most manufacturers have this feature as standard, to avoid damaging AC compressor and components, not for the extra hp.

Would it damage from one or two over revs? Probably not, but constant high RPM on a track, I would say you're asking for it to fail. I don't know of anyone that's done it, and there's probably a good reason. 

[Murray_Calavera]

On 5/30/2022 at 6:39 AM, Chopstick Tuner said:

Most manufacturers have this feature as standard, to avoid damaging AC compressor and components, not for the extra hp.

Would it damage from one or two over revs? Probably not, but constant high RPM on a track, I would say you're asking for it to fail. I don't know of anyone that's done it, and there's probably a good reason. 

I was worried that was going to be the case. Probably not much else I can do to get better AC on the track 

[robbo_rb180]

I haven't looked at r33 wiring diagram for ac wiring but most systems of a pressure switch that will turn off the compressor if not enough or too much pressure. It will most likely cut out on high pressure if you change the settings in the haltech.
If need more airflow when wearing a helmet get an external blower fan and pipe the airflow over your neck, it helps a lot

[Murray_Calavera]

Yep, I'd say your right based on the Haltech settings -

[joshuaho96]

On 5/29/2022 at 2:48 PM, Murray_Calavera said:

Yep, I'd say your right based on the Haltech settings -

I can try taking some logs with an RB26 on the stock ECU to see roughly where the OEM RPM threshold is. 4500 RPM seems a little low to me but who knows.

[Murray_Calavera]

Nice, that sounds good. The more data the better!

[Kinkstaah]

I have had to do this with the LS in my car - The alternator hits max RPM at 5000RPM stock, so the answer is a larger pulley to slow it down so it still provides charge up at redline.

This is something you could feasibly calculate for your AC pulley, but would be a pretty big undertaking and would affect your AC ability at lower rpm.

Keep in mind that the AC compressor only kicks on for a few seconds then switches off again (again, they never operate all the time). So it can switch on in hairpins and still provide the cooling it's supposed to if you time it right. Thats why I did the LS swap after all, I get low-down AC as well as low-down torque at 3000-4500rpm.

[joshuaho96]

On 5/29/2022 at 4:29 PM, Kinkstaah said:

I have had to do this with the LS in my car - The alternator hits max RPM at 5000RPM stock, so the answer is a larger pulley to slow it down so it still provides charge up at redline.

This is something you could feasibly calculate for your AC pulley, but would be a pretty big undertaking and would affect your AC ability at lower rpm.

Keep in mind that the AC compressor only kicks on for a few seconds then switches off again (again, they never operate all the time). So it can switch on in hairpins and still provide the cooling it's supposed to if you time it right. Thats why I did the LS swap after all, I get low-down AC as well as low-down torque at 3000-4500rpm.

AFAIK since the 2000s a number of cars have variable displacement compressors to improve AC efficiency so the behavior in those systems will be different compared to a fixed displacement unit that has to cycle on and off.

[GTSBoy]

The other thing to keep in mind is that it is not at all good to ask the clutch to pull in at high rpm. If you do not prevent it pulling in up high, then it will, and the clutch will cop a hammering.

[Kinkstaah]

On 5/30/2022 at 9:59 AM, joshuaho96 said:

AFAIK since the 2000s a number of cars have variable displacement compressors to improve AC efficiency so the behavior in those systems will be different compared to a fixed displacement unit that has to cycle on and off.

Yep, 100% - But the Skyline and the LS are the 'old' style, which worked well for my purposes. By working... less well.

[The Bogan]

Have a look at the Dodge Demon interchiller set up

I "think" it keeps the A/C running at WOT

In saying that, it was designed and sold as a 1/4 mile car and the rev limit is 6500

[joshuaho96]

On 5/30/2022 at 1:00 AM, mlr said:

Have a look at the Dodge Demon interchiller set up

I "think" it keeps the A/C running at WOT

In saying that, it was designed and sold as a 1/4 mile car and the rev limit is 6500

Even if it couldn't actually run AC from idle to redline, the way the system is described means it can use the water to air charge cooler to help absorb the transients until the compressor can kick on again. It also seems to be designed for drag passes so there's a definite start/end to when that transient would be in the intended use case.

[The Bogan]

On 30/05/2022 at 6:57 PM, joshuaho96 said:

Even if it couldn't actually run AC from idle to redline, the way the system is described means it can use the water to air charge cooler to help absorb the transients until the compressor can kick on again. It also seems to be designed for drag passes so there's a definite start/end to when that transient would be in the intended use case.

Yeah but I read somewhere that the aircon does not drop out at WOT, although god knows where I read it, it was when I was researching interchillers

But I don't believe they use a different compressor between the NA Dodge and the supercharged and interchilled version 

Again, not to sure, but maybe Dodge have found an answer to your particular conundrum 

 

Maybe not

 

[joshuaho96]

On 5/30/2022 at 5:16 AM, mlr said:

Yeah but I read somewhere that the aircon does not drop out at WOT, although god knows where I read it, it was when I was researching interchillers

But I don't believe they use a different compressor between the NA Dodge and the supercharged and interchilled version 

Again, not to sure, but maybe Dodge have found an answer to your particular conundrum 

 

Maybe not

 

I'm pretty sure the AC cut at WOT in most cars is just to reduce the parasitic loss when requesting maximum power. The RPM limit though is almost certainly determined by what the compressor can take without destroying itself.

[The Bogan]

On 31/05/2022 at 11:31 AM, joshuaho96 said:

I'm pretty sure the AC cut at WOT in most cars is just to reduce the parasitic loss when requesting maximum power. The RPM limit though is almost certainly determined by what the compressor can take without destroying itself.

I don't think your picking up what I'm putting down

Does aircon cut at WOT on 99.9999% of cars yes

But, does the HP loss from from a running aircon translate to enough to justify shutting it down when running a interchiller with the Dodge Demon 

I read that Dodge keep the compressor going, is it a "special" compressor, is it that the RPM limit is 6500rpm and their techs think the compressor can handle those revs, in the end the compressor works the same at idle or 6000rpm, faster does not equal colder

In the end it's a difference of only 2000rpm for the Demons compressor 

The issue I see is spinning the compressor up high RPM, OEM seems to think 4500 rpm is fine, what fudge factor % was reduced for warranty 

Maybe the compressor can spin up to 8000rpm, whilst only loosing 5 hp???

Maybe the compressor explodes at 6000 rpm????

Maybe the compressor in a Dodge Demon is special 

Maybe I'm talking out my arse and have not remembered correctly and the Demon compressor shuts off lime every other one

In the end Tesla use a electric motor to run their AC compressor, which runs at a constant speed, maybe you could jerry rig one of those puppies

Electric power steering pumps are a common mod now, hell I want to fit one to my current beastie

Maybe the next fad will be electric aircon compressors

 

TL;DR I'm bored at work

[Duncan]

Electric AC is common I think, pretty much every Hybrid or BEV needs it

[Chopstick Tuner]

Long story short, if you plan to do it you'll likely be pioneering constant AC on an RB track car, and will be letting us know how good or bad the idea went. 

Curious to see if an electric AC pump can be made to work in there, equally curious to see if your stock one explodes at wot high RPM. 

Godspeed sir 🤣

 

[GTSBoy]

On 5/31/2022 at 11:53 AM, mlr said:

In the end Tesla use a electric motor to run their AC compressor, which runs at a constant speed, maybe you could jerry rig one of those puppies

 

On 5/31/2022 at 12:27 PM, Duncan said:

Electric AC is common I think, pretty much every Hybrid or BEV needs it

 

On 5/31/2022 at 12:52 PM, Chopstick Tuner said:

Curious to see if an electric AC pump can be made to work in there

And....no. You're not going to draw 3ish kW of power from a 12V supply.

BEVs and hybrids that use electric AC compressors are running them on the 42V standard that sort became the thing when such high power demand applications started to become a thing, or even higher voltages. This because..... they have higher voltage available.

You wanna rig up a special alternator capable of putting out 42V, then yeah, maybe.