AAR operation - can anyone explain how it works?

[kenikh]

What does the electrical lead for the AAR do? I always thought it was a non electrical item that used a bi-metallic strip, that when warm enough, adjusted airflow via expansion differential, to drop idle down. So what's the electrical connection do?

I am trying to figure out if the and EMS can control the AAR like an a IACV, to control idle speed.

[JFairman]

It's the resistance wire heater element on the bimetalic strip. Same thing on and inside the WUR.
These are ancient mechanical CIS devices that will not heat up and work properly without that 12 volt supply plug plugged in. They are not heated to operating temperature by heat transfer absorbtion from the engine they are heated by the 12 volt heat element wrapped around the flat bimetallic strip.

[Tom F2]

Kenik,

I believe that the electrical connection is for a heater that warms the bimetallic strip, as in the WUR.

I can't help with your second question.

Tom

[gavinc69]

That would be cool being able to bin the AAR and control it by the EMS instead.

[kenikh]

If I read you right then, there's a thermotime switch somewhere that tells the heater when to turn on/off and thus cause the bi-metallic strip to open/close the AAR. If so, then using the EMS to manipulate the AAR using duty cycle control should be easy peasy.

Am I reading you right?

[mark houghton]

Originally Posted by kenikh

If I read you right then, there's a thermotime switch somewhere that tells the heater when to turn on/off and thus cause the bi-metallic strip to open/close the AAR. If so, then using the EMS to manipulate the AAR using duty cycle control should be easy peasy.

Am I reading you right?

No there isn't any timed switch involved, just direct 12V power continuously on whenever the engine is running (powered from the rear fuel pump relay circuit). The AAR is open to its maximum position when cold and slowly closes as it heats up.

You wouldn't want to interrupt power to it once the car is fully warm, which would cause it to open back up and cause a high idle. You can experience the same effect a couple minutes after starting a car back up which had been shut down when fully warm. The AAR will slowly open while you're in the store buying a 6 pack or some cigs, and the car will idle really high the first minute or so on startup.

[kenikh]

Well, my car idles high for 15 minutes. I've tried two different AARs, so either my 12v supply isn't working or my EMS is doing some crazy $#!t to fight the AAR. Which means I should probably just take a voltage meter to the AAR power leads and see what the reading is...

[jpnovak]

Kenik,

how do you have it connected?

You should see about 35-38Ohms across the terminals of the AAR. It only needs static 12V. No PWM needed.

you can test on the bench. apply 12V and then wait. The half moon disc should close off in about 3-4min. Its relatively slow. If it moves, it is working. It could be sticking inside and you can drill the 4 rivets to clean out. Then replace with screws.

I don't really see the need to connect to an EMS since it operates independently.

[mark houghton]

Originally Posted by jpnovak

Kenik,

how do you have it connected?

You should see about 35-38Ohms across the terminals of the AAR. It only needs static 12V. No PWM needed.

you can test on the bench. apply 12V and then wait. The half moon disc should close off in about 3-4min. Its relatively slow. If it moves, it is working. It could be sticking inside and you can drill the 4 rivets to clean out. Then replace with screws.

And/or, alternately heat the thing up in the oven @ 150 or so, then put the whole unit into the freezer (if your wife will let you). First note the degree that it's open when warm, then after a few minutes in the deep freeze. If it doesn't show any movement then there may be something mechanically wrong with the innards.

Go here Idle is high and look at the picture I posted at post #28...pict of a cold AAR. The resistance values will tell you if the internal heating element is open, and if checking for voltage at the plug be sure that your pumps are running or you'll read zippo volts.

[smurfbus]

I installed a hand throttle to replace the AAR. Simplicity and looks FTW. I think EMS needs an idle motor if you skip the AAR.

[kenikh]

So is the AAR a timed device, meaning that the 12V heater is supposed to expand the bimetallic strip and thus move the AAR plug over a fixed period of time, based on calculation of the coefficients of thermal expansion? Is there no actual input or feedback in the equation? If so, that is just WEIRD!

[kenikh]

Originally Posted by jpnovak

Kenik,

how do you have it connected?

You should see about 35-38Ohms across the terminals of the AAR. It only needs static 12V. No PWM needed.

you can test on the bench. apply 12V and then wait. The half moon disc should close off in about 3-4min. Its relatively slow. If it moves, it is working. It could be sticking inside and you can drill the 4 rivets to clean out. Then replace with screws.

I don't really see the need to connect to an EMS since it operates independently.

Stock connector to the stock harness is how I have it connected. The only thing that isn't stock is that I am using an EMS for spark, which has some ignition curve calcs for cold start that you can configure. That said, they don't seem to have any effect upon the idle speed.

[Ronnie's.930]

Originally Posted by kenikh

So is the AAR a timed device, meaning that the 12V heater is supposed to expand the bimetallic strip and thus move the AAR plug over a fixed period of time, based on calculation of the coefficients of thermal expansion? Is there no actual input or feedback in the equation? If so, that is just WEIRD!

Not timed - the strip is gradually heated (gradual, as opposed to sudden, because the amp draw is very low), causing the disk to slide into the closed position, and with the engine running (relay energized) the strip continues to be heated and the disc remains in the closed position.

The colder the strip is to begin with, such as if the ambient temp is cold, the longer it takes for the strip to heat, and thus, the high idle lasts longer.

[kenikh]

I've concluded the AAR is a ridiculous device.

[T77911S]

it is a very crude device but it works for what it is intended to do, raise the RPM's ONLY when cold.

it is a slow acting device so it can not react fast enough to REALLY control the idle.

the only timing it has is the amount of time it takes it to heat up an lower the idle.

testing is apply 12v and see if it closes. check for 12v at the connector.

the great thing about this and CIS is it is very reliable.
go with a euro setup like me and i have no electronic crap that can break.

[Tom F2]

My 77 has a hand throttle, which suggests that Porsche lacked confidence in the AAR.

[dap930]

Kenik,

You could replace it with a 2-wire Bosch IAC valve. Then use the ECU to pwm control warmup via warmup table. But, you would have to do some wiring and add a "coolant" temperature sensor to engine.

[kenikh]

Originally Posted by dap930

...you would have to do some wiring and add a "coolant" temperature sensor to engine.

Already in place.

[16Volt]

Not sure if tech has improved but PWM control of a IAC is not an easy setup in terms of programming. Been there done that, no thanks.

Like I said Kenik, try isolating the idle zones on your ignition map. If you are stubbornly dedicated to making your life hard I have a few IACs laying around you can toy with.

[kenikh]

^ you know me.