weird problem during traffic jam yesterday

[stugray]

I just ran a datalog of the car sitting idling after 100% warmup.:
https://docs.google.com/spreadsheet/...Wc&usp=sharing
With the AC Off, the engine coolant temps cycle from 203 (fan off) to 190 (fan on).
And the intake temps were ~115 (ambient is 39)

With the AC On, the engine coolant temps were a solid 195 (fan on continuously).
And the intake temps were ~125 (ambient is 39)

So there is hard data that the AC is dumping heat into the engine coolant and running the intake air temp higher.
AND data that demonstrates that the ECU software behaves differently with the AC on (it left the fans on continuously as mentioned above)
Why did the engineers that designed the system make it do that? - because they know that running the AC will generate more heat.

If it had been over 100 degrees ambient, I would have also seen the AC compressor turning off, but I didnt in this case.

Now back to the OPs issue:
I believe that the AC compressor was kicking on & off and messing with your idle.
But I'm just a lowly engineer and I didnt sleep at a holiday inn express last night

[stugray]

Originally Posted by zooki

I guess I took exception to the line "When you argue with an engineer you make yourself look stupid". Kinda condescending, no?

My condescending comment came only after:

Originally Posted by gramicci101

That's about the dumbest thing I've ever heard...

And

Originally Posted by J_kennington

.... You almost had one part right though, AC is a setup of heat exchangers, NOT heat pumps.

Why is that when engine tuners, auto painters, & mechanics tell someone on these forums that they are wrong, they get all kinds of thanks for sharing.
When an engineer mentions their credentials, everyone gets all tweaked?
Truth is generic "engineers" (assuming they actually have a degree) only have one thing and that is "proof that they were at least above average in technical skills at least once in their lifetime".
That is all.
Perhaps I should have said: I am an aerospace/electrical engineer with 20 years experience in high end thermal control & monitoring systems.
Would that have made me sound like less of a ****?

[zooki]

I would have to think that the thermal load of an engine at idle, even with the AC on, is less than an engine pushing a car down the highway. Much lower. And the engineers should be able to take that into account and design the cooling system's airflow to accomodate that, even at idle. How many horsepower would you figure one if these motors uses idling with the AC on?

[stugray]

Originally Posted by zooki

I would have to think that the thermal load of an engine at idle, even with the AC on, is less than an engine pushing a car down the highway. Much lower. And the engineers should be able to take that into account and design the cooling system's airflow to accomodate that, even at idle.

I never said that the car was going to overheat.
However, think about; greater than 100 degree weather, engine heat soaked, engine bay heatsoaked, road heatsoaked, and cars in front of you blowing hot air all while not moving. Not the best time to add even more heat to the mix.

When I lived in LA and passing through Vegas during the heatwaves, they would even tell you on the radio to not run the AC in a traffic jam as it was the #1 cause of breakdowns.
Maybe that dates me....

[skyloran]

Originally Posted by Honeydew

its really interesting good thing it's not something wrong with my car.. i was pretty scared for a while @-@

Never had this happen on Manual. why you get an auto at first place?

[Minovsky]

Originally Posted by skyloran

Never had this happen on Manual. why you get an auto at first place?

kind of tired of these questions...

[SirBrass]

Originally Posted by skyloran

Never had this happen on Manual. why you get an auto at first place?

and AT vs. MT is totally unrelated to the issue at hand.

And I think the reason people get torqued at us engineers when we give an engineer response is that we're generally more blunt than others (worse bedside manner if you will). Other engineers won't interpret the response as condescending, just direct. Other folks, however, seem to need to have their feelings soothed first. You don't call an engineer for that, which is why we usually aren't ever actually asked to talk when in front of a company's investors.

[stugray]

Originally Posted by Honeydew

kind of tired of these questions...

When I traded in my MT supra for an AT Solara, it was because I had a 3-4 commute in bumper-bumper traffic almost everyday. My knee could not take it anymore...

Originally Posted by SirBrass

, which is why we usually aren't ever actually asked to talk when in front of a company's investors.

LOL! I definitely agree. I have been known to say things like "I am not afraid of the customer" when I have to stand up to them and explain that they are wrong.
So I dont get invited to the hug-fest type of meetings, only the technical ones.

[SirBrass]

Have you seen the "red lines" video about what project managers are like from the engineer's perspective?

http://www.wimp.com/theexpert/

SOOOO glad I'm a contractor now, not a direct. I've been hit with the backscatter of this kind of project manager BS before and it still stank to high heavens. Being the one hit with it directly ranks just as high on my "Do not want!" list as becoming management.

[Luis_GT]

Originally Posted by stugray

I'll try to explain slowly....
Air Conditioners are heat pumps. They pump heat out of your interior into (wait for it) into your radiator (the thing trying to cool your engine).

AC systems take quite a bit of power: both HP from the engine and extra electricity for the fans (more drag on the alternator).

So while sitting in bumper to bumper traffic you are running a car in a way that generates the most heat while providing it the minimum cooling capability.

The system can detect the rising temps in the cooling system, first the car will turn on the electric fans to try to provide extra cooling for the radiator.
It even has more than one speed for those fans.

If that is not enough, it will take further measures and turn off your AC compressor. Why? because it knows that it generates more heat.
So I will rephrase "People who know what is good for their cars will not sit in traffic, not moving, with their air conditioner running"

um, wrong...

A/Cs have their own separate radiator, which is actually called an condensor. The only thing in the A/C system that runs through the radiator are the heater cores, which are used to heat the car, and are often closed when the system is set to throw cool air. The only reason the car runs hotter when the A/C is hot is due to the force required to run the A/C compressor.

Our cars have a built in failsafe that disengages the A/C when the engine demads more power to run (when accelerating hard, or when the engine is cold)

I've sat in 2 hours of bumper to bumper traffic, and have never had an issue with the A/C shutting off, or erratic idle.

Edit: Just noticed the condensor is in front of the rad, poor design is the reason it'll overheat... had the condensor been smaller (like on my bimmer which is 1/2 the size of the rad along with an extra front mounted fan) or placed behind the radiator it would be a non issue.

[stugray]

Originally Posted by Luis_GT

I've sat in 2 hours of bumper to bumper traffic, and have never had an issue with the A/C shutting off, or erratic idle.

I notice my car cycling the AC compressor on & off all of the time.
It will either do it if the engine gets too hot or if the temperature in the cabin reaches the setpoint on the dash (no point in cooling more if it is cold enough)

Originally Posted by Luis_GT

Edit: Just noticed the condensor is in front of the rad, poor design is the reason it'll overheat... .

Pretty much every car is like this.

[Luis_GT]

Originally Posted by stugray

I notice my car cycling the AC compressor on & off all of the time.
It will either do it if the engine gets too hot or if the temperature in the cabin reaches the setpoint on the dash (no point in cooling more if it is cold enough)


Pretty much every car is like this.

yes, but not every car has a radiator that's thiner than the condensor