What determines the duty cycle of the A/C compressor?

[LtNoogie]

Since there is no real temperature setting like higher end cars, I was wondering what determines how long the compressor stays engaged or not?

I've always maintained, correctly or incorrectly, that the compressor duty cycle is preset at the factory. The temp gauge on our Yaris allows us to mix warm air in with the cold to make the air more comfortable.

The reason I ask is that on balmy nights, I like to cruise the boulevards with my windows down but with the A/C on. I like the cool air on my face but being able to see and hear the action on the streets.

My GF says, I'm wasting energy by doing this. I tell her that the A/C uses the same energy all the time that it is turned on whether the fan is set to fresh air or recirc or whether or not we roll up or down our windows.

Thanks

[Yaris Hilton]

I think it's the outlet temperature of the refrigerant coming out of the evaporator.

[ka0sx]

the only difference between recirc and fresh is that fresh air draws outside air and cools it. The recirculation is used to make the air even colder as the cooled air is then drawn back in and cooled again, the on times of the compressor are the same on the coldest setting.

however as Yaris Hilton points out if the outlet reaches the set temp it turns the AC off until it needs to cool again, so in turn you probably are wasting just a tad more energy.

The only thing is that you are probably reducing maybe 1/2 mpg running the AC in a car like this so there shouldn't be an argument over something like this. I don't care how much of a tree loving into the green hype hippie someone is. 1/2 mpg is not going to change anything.

[CTScott]

I think that Toyota does some interesting tricks with the compressor duty cycle to avoid completely bogging down the car. The A/C Amplifier (it's ECU) has speed and RPM inputs and the ECM has a control signal to it called the "variable control prohibition signal".

[LtNoogie]

I find that when the A/C is on, I tend to manually shift my tranny because it can tend to bog down. One of these days, I'll find out what the annoying vibration is coming from. Those of us with the Blitz S/C are hearing it with the A/C on.

[Kaotic Lazagna]

Yeah, the A/C bogs down my car enough for me to down shift much earlier to stay in power.

[ka0sx]

Yeah, the A/C bogs down my car enough for me to down shift much earlier to stay in power.

ECU disables the AC when you WOT(withing 10%) =)

[Kaotic Lazagna]

Yeah, I'm almost never in WOT. hahahaha

[BailOut]

The only thing is that you are probably reducing maybe 1/2 mpg running the AC in a car like this so there shouldn't be an argument over something like this. I don't care how much of a tree loving into the green hype hippie someone is. 1/2 mpg is not going to change anything.
Actually, running the a/c is a 6-11% hit on MPG any time the compressor is cycling, which is much more often than not. That makes it exponentially less efficient than your initial thinking, and puts it well into the realm of measurably using more energy under "normal" operation, and measurably wasting energy if one has the windows down at the same time.

[LtNoogie]

Actually, running the a/c is a 6-11% hit on MPG any time the compressor is cycling, which is much more often than not. That makes it exponentially less efficient than your initial thinking, and puts it well into the realm of measurably using more energy under "normal" operation, and measurably wasting energy if one has the windows down at the same time.

But the question boils down to whether or not windows down affects how often the compressor is running.

If I run the A/C on fresh, the drop in temperature across the evaporator is purely based on the input of outside air.

If I run the A/C on recirc, I can see how windows down would not allow air conditioned air from being the cooler input to the evaporators.

[PETERPOOP]

the a/c definately bogs me down. I find myself needed to give it a lot more gas; especially if i am staying in 1st gear (driving out of my driveway or parking lots).

[cali yaris]

I can't really post in here. :biggrin:

[Yaris Hilton]

But the question boils down to whether or not windows down affects how often the compressor is running.

If I run the A/C on fresh, the drop in temperature across the evaporator is purely based on the input of outside air.

If I run the A/C on recirc, I can see how windows down would not allow air conditioned air from being the cooler input to the evaporators.

I believe you've got it right.

[yaris-me]

But the question boils down to whether or not windows down affects how often the compressor is running.

If I run the A/C on fresh, the drop in temperature across the evaporator is purely based on the input of outside air.

If I run the A/C on recirc, I can see how windows down would not allow air conditioned air from being the cooler input to the evaporators.

Long you have a hard head. If you drive with the windows up and it doesn't matter fresh or recirculate, the temperature in the car would get lower and you would reduce the fan speed which would reduce the load on the compressor which would reduce fuel consumption. Your GF is correct.

[ddongbap]

I don't even notice the difference when the AC is on or not. My dyno says theres only a 3hp difference.

I'm going to be tracking with the AC fully on.

[Lafiro]

Don't notice the difference? LOL stop kidding yourself.

So I took the diagnostic tool and plugged it into the car a few months ago. And I noticed something rather interesting.

At idle the engine is under little load, maybe 10%.

When the engine is in drive, but at a standstill, it jumps to around 27-30% load.

And when the A/C is being used, the load on the engine jumps to 42-52%(I forgot the exact amount)

Now, when you hit the gas, no matter how much you stomp on it, the A/C being ACTIVE will reduce 20-22% of the engine. Which to our 106hp engine means roughly 20-22housepower is gone because of it.

Don't believe me, test the car yourself when you know the A/C just kicked in, and use a nice scanning tool with graphs.

I tested this on my friends mercedes. He took it to the dyno, so we know its HP/torque. At the end, simple math equated that with his engine load raising just a few percent, we multiplied that by the horsepower put down/at the crank. Noticed, it was the exact 20-22horsepower of the engine that was being used.

This is why in our car that 20-22HP makes a really big difference, but in my friends Mercedes putting down 518 at the wheels, it really doesnt feel like anything is on at all.

This makes me really sad to know how weak this 1.5 engine is, but at the same time, happy that it does so good on gas, and thats why I own it. That and I like how it looks/drives! lol

[LtNoogie]

I think you just fell for one of ddongbap's troll messages.

It doesn't take alot more hp before you do not feel the affect of the A/C. I don't feel the loss of power with A/C in my Jeep and it only has 210 hp.

[ddongbap]

Don't notice the difference? LOL stop kidding yourself.

So I took the diagnostic tool and plugged it into the car a few months ago. And I noticed something rather interesting.

At idle the engine is under little load, maybe 10%.

When the engine is in drive, but at a standstill, it jumps to around 27-30% load.

And when the A/C is being used, the load on the engine jumps to 42-52%(I forgot the exact amount)

Now, when you hit the gas, no matter how much you stomp on it, the A/C being ACTIVE will reduce 20-22% of the engine. Which to our 106hp engine means roughly 20-22housepower is gone because of it.

Don't believe me, test the car yourself when you know the A/C just kicked in, and use a nice scanning tool with graphs.

I tested this on my friends mercedes. He took it to the dyno, so we know its HP/torque. At the end, simple math equated that with his engine load raising just a few percent, we multiplied that by the horsepower put down/at the crank. Noticed, it was the exact 20-22horsepower of the engine that was being used.

This is why in our car that 20-22HP makes a really big difference, but in my friends Mercedes putting down 518 at the wheels, it really doesnt feel like anything is on at all.

This makes me really sad to know how weak this 1.5 engine is, but at the same time, happy that it does so good on gas, and thats why I own it. That and I like how it looks/drives! lol

I've fully dynoed my car with ac on and off. There was only a 3 whp / wtq difference.

Third gear pull, on a 95degree day.

Anyways, try to be little me all that you want, and tell me more about how I'm kidding myself. I've dynoed the Yaris. And the Yaris isn't a Mbenz.

I think you just fell for one of ddongbap's troll messages.

It doesn't take alot more hp before you do not feel the affect of the A/C. I don't feel the loss of power with A/C in my Jeep and it only has 210 hp.

Normally I troll, but I'm speaking truth right now.

[cali yaris]

Lafiro, what "engine load" are you scanning exactly?

is this from the OBDII?

[IllusionX]

Does the AC on the yaris really cycle? I believe it stays on all the time, untill you turn it off. What you hear kicking on and off is the radiator fan...

[Yaris Hilton]

No, the compressor definitely cycles.

As for whether or not you can feel the difference, well, some people wouldn't know the difference if two cylinders weren't firing. If you pay close attention, and particularly if you measure fuel mileage, you can tell the difference even in huge V8 powered vehicles. But it's proportionately a greater effect as you go to smaller engines with less total power.

[ddongbap]

No, the compressor definitely cycles.

As for whether or not you can feel the difference, well, some people wouldn't know the difference if two cylinders weren't firing. If you pay close attention, and particularly if you measure fuel mileage, you can tell the difference even in huge V8 powered vehicles. But it's proportionately a greater effect as you go to smaller engines with less total power.

crappp..... i'm missing some pistions.....

[Yaris Hilton]

crappp..... i'm missing some pistions.....

Don't you just HATE it when that happens? :biggrin:

[IllusionX]

No, the compressor definitely cycles.

As for whether or not you can feel the difference, well, some people wouldn't know the difference if two cylinders weren't firing. If you pay close attention, and particularly if you measure fuel mileage, you can tell the difference even in huge V8 powered vehicles. But it's proportionately a greater effect as you go to smaller engines with less total power.


explain. Actually, i do feel the difference in power when the AC is on, but... when the AC is cycling... ???

[ddongbap]

Don't you just HATE it when that happens? :biggrin:

I DO! But I can't tell when it happens.

[47_MasoN_47]

I could tell the difference in power in both my Yaris and my old Ranger if I had the AC on. The difference in my Ranger wasn't as significant as in the Yaris, but that's probably because it had a lot more power than it needed anyway (I had the 4.0 litre V6 in a 2wd). If I'm going uphill I've gotten to where I just turn off the AC no matter the temperature because it seems like I'll never make it if the AC is on.

[Lafiro]

Lafiro, what "engine load" are you scanning exactly?

is this from the OBDII?

Hey!

Yes this was with some scanner with a live graph that I borrowed from my friends shop one day to play around with.

But its pretty accurate, I mean I know its just a computer, but when the A?C is ACTIVE I know for a fact that amount of HP is gone because engine load reaches 100% faster, and pressing the pedal faster ot harder to the floor didnt make it faster when it was on. The feeling of lost power was very obvious. And this was done on the same level long stretch of a driveway, so hills have nothing to do with what I felt + the scanner results displayed via OBDII.

[IllusionX]

The AC compressor has a clutch that engages and disengages that is what they are talking about cycling, it engages as needed.

The AC compressor stays engaged, until the AC is turned off....

[ddongbap]

This thread is going to be another one of those threads where people just spout out information that they've heard.

I've dyno'd the car, with and without the AC on. 3 whp difference.

[Lafiro]

Alright, the clutch is engaged when its ON, hence why cold car comes out the vents, and then its disengaged, meaning its OFF, meaning also NO load on engine, which is why the air gets warmer. You know when its engaged or not, the car either feels faster for a minute, and then it doesn't.

My guess is that ddongbap dyno'd his car just when the compressor disengaged.

Now lets see you argue me wrong on my hypothesis.

[cali yaris]

some people wouldn't know the difference if two cylinders weren't firing.

unplug one coil and try driving. Anyone would notice that.

Meanwhile, I still don't know what "load" is measured by OBDII. Trying to get educated here, help me out!

[CTScott]

unplug one coil and try driving. Anyone would notice that.

Meanwhile, I still don't know what "load" is measured by OBDII. Trying to get educated here, help me out!



Calculated Engine Load
California Air Resource Board (CARB) defines this as airflow divided by peak air flow. Peak air flow may be adjusted for altitude via barometric means if available. For diesel engines, the number is current output torque divided by peak output torque at current rpm. We have noted that vacuum leaks can have dramatic effects on this value.

[mikenacarato]

The ac compressor clutch does NOT stay engaged all the time when the ac is on. the thermistor (toyota term), cold control switch, or its also knows as an ac thermostat. it is in the climate unit and should be stuck somewhere in the fins of the evaporator. and as yarishilton said, it measures the temp of the evaporator.

[tazrulesny]

Don't take my word for it, go turn your ac on then actually watch the compressor, you will see and hear when it engages and when it disengages. Just because your ac light on the knob is on does not mean the compressor clutch is engaged. :laugh:

Hahahahah that cracked me the hell up. Guess when my head lights are on doesn't mean my car engine is still running huh? :thumbup:

[ozmdd]

A/c compressor clutch turns on and off as the unit cycles. You still get cold air if the fan is blowing air across the cold coils. When the system needs to compress again (to keep the coils cold), it re-engages the compressor pulley clutch. If you have the ac "on" and listen with the hood open, you will be able to clearly tell when this process occurs.

[Lafiro]

Exactly.

Ok fact is, even though the light is on that says the A/C is on, does NOT mean it is engaged 100% of the time.

It only turns the compressor on for a certain amount of time, then turns it off for a certain amount of time. Either that or it does so by temperature somehow, depending on where the knob is turned too.

So for everyone to understand this:
You are is losing 20%(on our stock engine) or so of power when the A/C ( the compressor ) is engaged! And just to clarify one more time for everyone, the compressor is NOT engaged 100% of the time, but it cycles on and off.

This should be the end of people giving out wrong information.

ozmdd is right as well (post above mine).

[ddongbap]

So, 20% of 500whp, is 100whp. Is that how thats works?

[ddongbap]

Exactly.

Ok fact is, even though the light is on that says the A/C is on, does NOT mean it is engaged 100% of the time.

It only turns the compressor on for a certain amount of time, then turns it off for a certain amount of time. Either that or it does so by temperature somehow, depending on where the knob is turned too.

So for everyone to understand this:
You are is losing 20%(on our stock engine) or so of power when the A/C ( the compressor ) is engaged! And just to clarify one more time for everyone, the compressor is NOT engaged 100% of the time, but it cycles on and off.

This should be the end of people giving out wrong information.

ozmdd is right as well (post above mine).
I'm not trying to disprove the fact that the AC drains power. My point is that it doesn't drain THAT much power.

3WHP difference. The AC was turned on after a few dyno pulls. So the AC was off for a while. The air was ice cold during the first AC pull. So the AC had to be fresh. Now, this might just prove that the clutch engagement system is intelligent, and turns off the AC during high load?

Now, this part is me theory crafting. A lawnmower engine has 2-3ish HP. I don't think one of these would have any trouble powering a AC compressor. It kind of seems high price to pay to run the AC which'll take 20hp.

[Yaris Hilton]

Now, this might just prove that the clutch engagement system is intelligent, and turns off the AC during high load?

Yes, actually most modern cars do disengage the AC compressor at or near wide open throttle.

[ozmdd]

Yeah I found it amusing as well.:biggrin:
You should really quote who you are talking about. I am assuming you are saying this for illusionx?


Again, you should quote who you are posting about, who is giving out wrong information? Illusionx is or was the the only one on here that thinks that the compressor is engaged 100 percent of the time. There have been several post to explain the opposite since that post. :iono:

True, quotes are helpful, but mine wasn't directed at anyone, other than simply stating some facts relevant to the thread. :thumbup:

I will quote more in the future.

[LittleRed]

I put in a AEM cold-air intake and my car no longer bogs down with the A/C on...apparently the engine is starved of air under stress...its really easy putting it in....well worth the $150... i also use fuel system cleaners in it on a regular basis and use 91 octane gas..its really quick now

[NH3R717]

22 hp is a ridiculous amount of power for a car a/c. 22 hp = about 16kw. Your home A/C might pull 2-3kw. hp and kw = power the same exact thing but different units.

[krolos]

I have owned V8 trucks, and other small 4 cyl. cars with Ac.
And I can tell you my Yaris has been by far the most sufficient with AC on, the gas mileage changes very little, if at all, yes it does bog the engine down a little,
but for a 1.5 I would say it is pretty good, and really not a whole lot.

33,000 miles on 2008 sedan, and no problems.

[Yarisduder]

22 hp is a ridiculous amount of power for a car a/c. 22 hp = about 16kw. Your home A/C might pull 2-3kw. hp and kw = power the same exact thing but different units.


+1 000 000 000

That's what I wanted to say!