Gunners AC Dilemma

[Gunner]

So I have this dilemma, the re is no need to ask questions about the circumstances in which this dilemma has arisen, we just need a solution.

My mirage is hectic, and I drive it really fast all the time, constantly revving between 3000-9000rpm, because of this my AC cant keep up, it isn't designed to spin as fast as it does, and so, disengages the clutch, so when it is hot, which it always is this time of year, I need to underdrive it so I can keep cool while driving really fast in my hectic mirage.

I'm not a mathematician, nor am I an AC technician, so I need some help with 3 things;

How slow will an AC compressor compress at?

At what RPM is a compressor most efficient?

Can I achieve this rpm band by underdriving the AC compressor?

Any help would be appreciated.

[ke70dave]

those questions are somewhat impossible to answer. you will need a data sheet on the compressor, which wont be very easy to get.

you could be tricky, and put a switch on your throttle, so when you hit say more than 80% throttle, the AC clutch turns off.

[Anthony]

Maybe the compressor trigger wire goes via the ECU, and the ECU has determined by your driving inputs that you must be racing for pink slips and would therefore prefer the ac turned off. :)

[Gunner]

I want the ac on pretty much 100% of the time, excluding idle, I can keep it turned on thats easy, but it turns off at 4000rpm, which will not achieve what I want, if I can have it operational at say 8000rpm, I can achieve the result I want. But if its spinning that fast I dont think it would end well, hence why I want to underdrive it.

[Hen may possibly be a nut]

Make a larger AC pulley (or smaller crank pulley) and experiment.

PS, we need pics of the Mirage so we can judge how hektik it really is (on a scale from 1 to fooli). Of course, chrome rims give extra points.

[Anthony]

why wouldnt you want it on at idle? thats exactly when you need it isnt it?

if the ECU determines > 4000rpm to be sports driving and hence needs ac turned off, it doesnt matter how under-driven the ac comp is, it will still turn off. you still need to let the aircon controller do its thing (turn the compressor on and off when it needs) so forcing it on wont work either but you should try and determine what else is stopping. could be a much easier fix than changing clutch pulleys etc (not a fun or easy job!)

It could be high pressure switch on the AC line stopping things due to the system being overcharged with gas.this fits with the hotter weather problems. many possibilities. :)

[Gunner]

Guys forget the story, the mirage is not hectic, come on do you really think it revs to 9k, theres no mivec v6 in there. I have a design where I need to refrigerate something at high rpm, it is that simple (not the process, but the reasoning), all I need to know is how to keep the fucker on and operational between 3000 and 8000rpm.


I'm sorry but I don't want to give to many details away, you never know whos watching :))

[lolwat]

technicaly you wont your ac compressor as as little as possible, thought of a regas, if the system is working correctly, the compressor shouldnt need to be on all the time and if you really wont it on all the time supply power to clutch switch and it should engage, and leave it on 24/7. But i imagine pressures would get way to high

[Gunner]

Yes thats why I want to underdrive it.

forget about making the car cool, that doesn't matter, as its not why I want it on all the time.

[Anthony]

Refrigerated intake? Perpetual motion machine?

Whatever you are doing, you need to understand the cutout in question before you over-ride it. Theres no blanket answer without knowing that.

[Gunner]

Someones a clever cookie, refrigerated intercooler for an 06 sti i have been toying with.

[spoon]

hook the compressor up to a constant power (ie ignition switched), and put a pulley on the compressor 2xdiameter of existing one so compressor runs 1/2 the speed. otherwise hook the existing switch (from computer) to a relay so instead of switching the compressor off above 4000RPM and on below that, to switch off below that and on above 4000RPM.

[timbo]

Perpetual motion machine would have been far more exciting gunner.

[Gunner]

there must be something wrong with me, cause i find ice cold intake charge far more exciting

[timbo]

haha agreed. i've always thought about refrigerated intake and whether it would be possible to maintain the power benefits without creating a power loss. are you going to run a "cold sleeve" around intake piping?

[Anthony]

They're basically the same thing :) At 6000rpm your EJ would be breathing 100 litres of air a second if it was NA. Since it's turbo and probably an EJ25 (not sure when they changed over in aus) thats more like 200 litres +. Every second. You're going to need a fairly serious refrigeration system to make the slightest difference to that air. :)

[KENut]

Wouldn't it be easier to go to an electric unit?
Search for hot rod or hybrid solutions

[Gunner]

I have seen t work on diesels but not on a petrol engine, ideally the plan was to run it the same as a water to air cooler, but with refrigerant instead of the water.

[Anthony]

define work? I am not trying to put your idea down just playing devils advocate. I have given it some thought before though. The average engine will gain about 0.5% - 1.0% horsepower for every 4 degrees you can drop the intake temp. A standardish 4 horsepower AC compressor has no hope of taking 4 degrees out of an EJ intake charge, and even it did it would only give you 2-3 hp back (on the EJ) :S Admittedly this maths has many assumptions but as a rough guide it doesnt look good, you have to admit.

[Gunner]

No it doesn't, , used to go 4wdriving alot with te old man, there was some old bloke who rocked up one day, and at idle had steam coming from the bonnet, so we had a look as you do, and his cooler, (set up the same as water to air, but with ac system) was iced over.

I was a youngin, 12 or so at the time, and didn't understand it. Now with far more knowledge, I have been thinking about it, and a customer called me last week having a cry about heat soak, and wants to do something "cool" so I said I'd look into this. I like the idea, but it does seem alot like my "mechanically assisted" turbocharger hahaha. Alot of outlay not much gain, but that said, the Suby engine and ac layout, do kind of lend itself to the option.

I have been thinking of charging it with CO2 rather than r134 or whatever it is.

[spoon]

if its just for the drag strip, can use water to air intercooler and plumb the heat exchanger in passenger footwell into a tub filled with dry ice, will keep temps down, otherwise just put a water/alcohol spray onto the intercooler when it gets too hot - try the common fixes first i say

[Gunner]

WIll be fitting the huge water tank out of an RA wrx, and will run a custom spray bar (modified cry 02 spray bar) triggered by a hob switch to come on at 12psi, will be sprayed through a new hyperflow top mount.

[macca1590]

still on a/c drama in mirage? find the a/c on signal coming from the switch, remember might go through fan speed switch first cause u dont want ur a/c on with no fan or ur evaporator will ice up quick like, run that through factory thermostat and pressure switches to compressor, whenever a/c button is on and evaporator not iced and not low pressure and not high pressure a/c will be on, all through rev range