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]

Originally Posted by Kaotic Lazagna

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]

Originally Posted by ka0sx

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]

Originally Posted by BailOut

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.

[Yaris Hilton]

Originally Posted by LtNoogie

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]

Originally Posted by LtNoogie

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]

Originally Posted by 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

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.

Originally Posted by 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.

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