weird problem during traffic jam yesterday
 

So i was just stuck in traffic and for around 20ish minutes the car kept jerking back n fourth at 1st gear im in an AT frs. It would drop from 1k rev down to 500 and then back up while rolling.. Then the A/C started warming up and then it turned completely warm air for a good 5 mins... even while stopped it randomly went from 1k rev down to 5 etc etc.. not sure what happened is it just my car or is it normal?

I believe i have posted in the wrong topic how can i move this to the issues category?

Check the AT fluid level???

I'll bet that you began to overheat and the system shut off your AC compressor.

You arent really supposed to use the AC unless you are moving.

oh shoot really? =[ my 86 what have i done to u!!!!! i really didnt know :bonk:

For seriously? That's about the dumbest thing I've ever heard, but I could genuinely see Subaru saying it with a straight face.

On the manual if you bog the engine it will definitely jerk back and forth, which is typical of subaru engines. The AT version should keep itself from bogging in this way.

eh, are you sure you weren't barely hitting the pedal? at really slow speeds mine will "jerk".


as for the "ac not meant to be used unless moving"...ill...just leave that alone.

The jerking is the torque converter locking up. If you shift into 2nd before coming to a complete stop, it won't jerk.

The AC thing is "normal" in these cars. It's the AC compressor cycling.

I have these issues too ...but if you do a search it's somewhat normal.

I'd have to agree with the AC theory. Last week it was 90+ and I got to work a bit early so I was sitting in my car waiting to start. I had my AC on and my idle was very erratic. I turned off the AC and the idle went back to normal. I turned the AC back on again to see if the idle would go nuts and low and behold it did it again. I got out of my car and popped the hood to take a look. A few seconds after I popped the hood the the high fans turned off and idle went back to normal (with the AC on). I guess it just gets really hot under their. As soon as I shut the hood, the high fans turned on again and the idle went erratic. Heat and the high fans definitely seem to be a contributing factor.

I also have an auto and if I'm in first and the car gets up to 9 mph or a little higher and I let off the gas, the car will start jerking until it goes to second. I never noticed anything with the ac though.

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"

This week I took 2 cat naps in my car with outside temps in high 80's to low 90's. My car sat for about 30 minutes this way each time at work. If you leave the AC on 1 (for FRS), the idle will be erratic with fans cutting on and off. Leave the AC on 2 and it will be smooth and consistent with fans always on. No rough idle issues. When it was time to get up and pull into the main parking lot the car drove fine. I am in an manual however. Cannot say much for auto.

I know how it works, I just think it's stupid for the manufacturers to decide it's ok to turn off the AC if the car isn't moving. I'd rather have paid a few more dollars for a larger radiator than be stuck in a traffic jam on a hot day and have my AC shut itself off.

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

Coolant temp will be higher in traffic when the AC is off. This is because the fans only turn on when the the coolant temp reaches 100C. Try it yourself, turn off the AC in traffic and watch your coolant temp creep up.

With the AC on in traffic, the fan is always on and will keep coolant temps below 95C.

If the car was getting hot enough that it turned off the AC to prevent it from overheating you would most definitely notice the temp gauge running way too high.

Plus, it's not THAT hot in Canada yet, so it really shouldn't be having heat issues. I've had days where in BAD traffic the AC isn't as cold as it normally is, but it's still cold. I've never had it turn right off, or had the temps creep up (based on the gauge, not by accurate logging) either.

So, the fact my car has never overheated while not moving with the AC on means what?

Can you explain to me how the AC pushes heat into the radiator, since you know...it's not connected in any way. You almost had one part right though, AC is a setup of heat exchangers, NOT heat pumps. The condenser is what takes the heat, NOT the radiator. It then goes to the evaporator which once again, reduces heat. The ONLY part of the hvac system to deal with the radiator is the, heater.

As for the idle issue, you all do know there is a tsb out for that right?

If the ac blew warm air while the idle became erratic, that is a clue. It's either the ac system could not handle the heat and the pressure in the ac system shot up. This usually causes the compressor to stop because you cannot add more pressure, thus stopping the freon from circulating.
This scenario usually happens when the coolant temps cannot handle the heat and the cooling system simply overheats. This happens a lot in Manila because of the heat and bad traffic.
Things to check for are:
Radiator coolant level
Radiator cap might be leaking
Radiator fans might not be turning on that's why it happens during traffic
AC system might have sprung a leak and caused a vacuum leak which made the idle erratic

It means nothing (at least with regards to my argument)

The AC radiator and the engine radiator ARE STUCK TOGETHER.

You apparently never took thermodynamics.
In the refrigeration cycle, a heat pump transfers heat from a lower-tempeature heat source (the evaporator in the passenger compartment) through the compressor (which makes the refrigerant HOT as it is compressed back to liquid) then it dumps that heat into a higher-temperature heat sink (The AC radiator).

The AC radiator IS ATTACHED TO THE ENGINE RADIATOR.
In SOME cars the AC radiator is INSIDE the engine radiator.

By running the AC you are dumping heat directly into the radiator. This is especially hard on the system when there is less air flow through the two radiators than when the car is moving.

When you argue with an engineer you make yourself look stupid.

that is true it wasnt that hot that day. hmm :bonk:

I'm not suggesting that the engine was running way too hot or about to overheat.

I was just pointing out that the ECU software cycles the AC compressor on and off for various reasons.
One can be for economy - No reason to run the AC at 100% duty cycle if the demand is only 20%. So it turns the AC compressor on and off via the solenoid clutch in the AC compressor.
The software can just decide to give less and less drive to the AC pump as it detects engine temps rise.

I thought I even heard of someone comment that their AC would not work after driving the car at the track hard because the engine temps were too high...

Tell ya what, I'll just say. "Sure" and leave it at that.

Fixed that for you.

Most(if not all) car manafacturers spend a lot of time and money making sure their cars will not overheat on hot days. If you've ever seen pictures of the "heat soak" buildings a lot of them have in Arizona you'll know that they leave their automobiles sitting in them, running, with all the accessories on for hours and hours. I find it really hard to believe Toyota skipped this step in testing. I would have to say its something else, and NOT normal.
As far as arguing with engineers, I've worked in the petrochemical industry for 20+ years, and can assure you engineers CAN and ARE wrong quite a bit. We in the operations side of things just love it when we get brand new engineers at work...it seems that some of them trade in their common sense for that sheepskin to hang on their wall.... :lol:

It's cool. Engineers are always correct. Even when they have nothing to do with engineering the system in question. Makes me wonder how every car I've ever owned has never raised a single degree in temp while running the AC.

we are all dumber for reading this nonsense...

I made it a point to call you out because you were blatantly wrong in calling ME out about how an air conditioner works.
And note: You never said Oops I am sorry I was wrong.

Oh I wasnt aware that you have run instrumented tests on your car in the past....
I can say for a fact: You are wrong. Running the AC DOES make your engine run hotter. Period.
One of the things I do for a living is instrumented thermal testing of systems far more complex than a car. SO even your "Even when they have nothing to do with engineering the system in question." is incorrect.

You said that an air conditioner was not a heat pump, it was a heat exchanger. You were wrong.

And it is 100% a fact that the running the AC adds heat to the engine's cooling system.
You dont need to be an engineer to understand this.

AND I never said that the OPs car was overheating or WAS going to overheat.
I merely stated that as the car sits in traffic with the AC running that the software will begin to do things to keep the car cool.
Such as turning on the electric fans and cycling the AC compressor more frequently.

I honestly have no idea why you even argued with that statement as it is fact.

And being an old fart we were always taught to not run the AC unless the car is moving.
I guess young kids these days think cars have always been perfect and have had computers in them to manage themselves.


I agree. Except in this case I was not wrong. I was being lectured about how an air conditioning system works by someone who does not know (apparently).

FACT: Running the AC dumps a huge amount of heat into the car's cooling system.
FACT: Running the AC adds a significant load to the engine.
FACT: The car gets less cooling when not moving.

Now you can debate whether it's bad for the car or not all you want, but the above are facts.
Or are they NOT facts just because I am an engineer and engineers are always wrong?

I didn't say you were always wrong, what I said was car manafacturers spend a lot of time testing for things like this. I guess I took exception to the line "When you argue with an engineer you make yourself look stupid". Kinda condescending, no? I've argued with a few, and I've been right. I've been wrong also, but it's not a given.
There has to be something else wrong with the car otherwise every one of these cars would exhibit this behavior in hot climates. I myself live in south Texas and last summer we had many 100+ degree days and my car never exhibited any of these symptoms.
So is my car the exception, or the OP's?

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

My condescending comment came only after:

And

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 ****?

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?

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....

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

kind of tired of these questions...

:offtopic: 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.

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...

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.

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.

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.

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