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Old 10th November 2011, 21:57   #106
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Default Re: A/C and fuel economy & How to use aircon optimally.

^^^
The Sanden system did cycle (In the SS80). In my experience the Subros system never did. But then it never really chilled also!

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Sutripta
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Old 11th November 2011, 10:57   #107
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Default Re: A/C and fuel economy & How to use aircon optimally.

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Originally Posted by anujmishra View Post
Is everyone sure that AC cuts off in Manual AC when certain temperature reaches? Is there any source of information for this?

If this was the case cars with smaller CC should sometimes should not feel load on engine(Atleast for some time). I have never felt this during my seven year of driving of 800. I was driving 800 with almost AC on for 80% and there was drastic power reduction when AC is switched on.

I feel people making statement based on his experience of Window AC at home.
I too share your views on this.
At home I usually set the temp at about 28-29C and fan speed to maximum most of time.It then switches on and off more regularly than if I set it at say 18-19C.
I do the same in my Getz as well.While traveling alone I set the temp more towards warmer side, but still on the blue though, and fan speed to 3.(say its equivalent to 28-29 at home).So obviously the car is not getting chilled and so AC is putting less burden on car resulting in better mileage.
And if I set the temp to max,extreme left of blue mark which is sort of equivalent to 18-19 for window AC,its putting lot of stress on engine resulting in low mileage.
In-fact keeping the temp to max and fan at lowest speed will result in lowest mileage IMO because it will take longer for a low speed fan to distribute the cool air in cabin.

Thats my own theory though.
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Old 11th November 2011, 11:38   #108
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Default Re: Air conditioner Load

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Originally Posted by Sutripta View Post
Hi,
If you cool air below its dew point, water will condense out. If you bring it back to its original temp, it now carries less moisture - it has been dehumidified. The RH value has dropped. Note though that if you just cool it below the dew point, though you will be precipitating moisture, RH now is 100%. Uncomfortable. Cold and clammy.

So you first cool the air to remove moisture. There are some standard rules (incorporated in tables) as to when a person feels comfortable in terms of temperature, humidity, wind velocity, whether clothed or not etc. Then you heat it to the degree needed.

Regards
Sutripta
See this chart,
Name:  aircon_comfort chart.jpg
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Source and more info:I.S.Vox : the voice of "indoor systems": Thermal Comfort

In degree celcius:
Name:  aircon_comfort chart.gif
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Last edited by jalsa777 : 11th November 2011 at 11:42. Reason: Better information
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Old 27th November 2011, 19:02   #109
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Default Re: A/C and fuel economy & How to use aircon optimally.

Few observations I have noted in our Baleno.

When the engine is really cold (say, in the mornings), before starting up the car, set the temperature knob to the highest (say 31 degree), switch on the A/C, switch on the auto mode, then crank the engine.

1) Even though the set temperature is higher than the outide temperature, the compressor gets switched on! The pipes leading from the compressor gets cold. Okay that the compressor gets cut off and on frequently, but what is the necessity for it to get switched on?

2) The cabin do not get heated up even after a good 2 minutes. On other instances when the engine is hot, we can feel the hot air at the grill inside the cabin fairly quick.

Deductions-

1) a) This might be to adjust humidity! Couldn't think of another reason.
b) Considering FE as the only criteria, even the automatic climate control is not as fuel efficient as switching off the A/C manually after maintaining the lowest fan speed and temperature.

2) There is no separate heater as such, at least in the Baleno. The hot air is obtained from the engine's heat alone.

Difference on the Chevy Beat - The compressor did not get on comparing to item 1) above. Does it mean that the Beat's A/C is not checking the humidity? If we switch on the A/C button manually, then the compressor gets switched on even if the temperature set was at the highest (31 degree). This is a confirmation that in modern auto A/C, the compressor do get off if the outside temperature is lower than the set temperature. In this light, the auto A/C is more fuel efficient than the old manual A/C for temperature settings above low. Item 2) stood true for the Beat too.

Last edited by thoma : 27th November 2011 at 19:26. Reason: adding test result for the Beat
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Old 28th November 2011, 09:49   #110
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Default Re: A/C and fuel economy & How to use aircon optimally.

The AC detects and controls the temparature inside the car, rather than out side.

The car heater works off the engine cooling system. There is an offtake from the cooling circuit to a small heat exchanger, normally in the fan circuit.

In ACC both AC and heater may come into play to control humidity, but in the normal Ac such is not the case. The AC is controlled by the AC button, and the heater by the thermostat. I have inadvertently switched the AC on in winter and both were on, till I switched the AC off.
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Old 28th November 2011, 10:16   #111
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Default Re: A/C and fuel economy & How to use aircon optimally.

Quote:
Originally Posted by thoma View Post
1) Even though the set temperature is higher than the outide temperature, the compressor gets switched on! The pipes leading from the compressor gets cold. Okay that the compressor gets cut off and on frequently, but what is the necessity for it to get switched on?
If the AC switch is ON, the compressor is switched on. And, it will try to cool the air.
Quote:
Originally Posted by thoma View Post
2) The cabin do not get heated up even after a good 2 minutes. On other instances when the engine is hot, we can feel the hot air at the grill inside the cabin fairly quick.
The heat to heat the cabin is taken from the engine coolant. So, when the engine is cold, there is no heat in the coolant, and hence no heat coming inside the cabin.


But then, yes.. Compressor turning ON in heating, is to control humidity.
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Old 10th June 2014, 15:43   #112
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Default Re: A/C and fuel economy & How to use aircon optimally.

Reviving this old thread. I have driven zen and swift in India.

Let me define the thermo setting in Swift: 25% area for Blue, next 25% white, next 25% again white, next 25% as Red.

I have notice if I keep the a/c setting in the second white section next to blue, the air from the blower is not as cold with a/c on. If the temp knob is pointed to blue then the air is colder.

Does this mean hot air is being mixed with cold air? If that is the case, then this setting is very inefficient for summers.

Does the compressor ever turn off in Swift for temp setting pointing to white next to the Blue?

In my zen, this setting used to turn off the compressor regularly but haven't been able to make out much of a difference in the Swift maybe because of its higher power.

Also, if the a/c switch is turned off and knob is pointing to the white section next to the blue section, the air is warm as if being heated. This reinforces the above observation and is true for both the cars.
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Old 10th June 2014, 17:33   #113
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Default Re: A/C and fuel economy & How to use aircon optimally.

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Originally Posted by Zappo View Post
Well, the moment the AC is on the the RPM goes up. You can check this if you have a tacho in your car. Even otherwise, when the car is standing still hear the engine noise the moment you switch on the AC. It goes up. This is because the engine now needs to generate more power to run the engine and at the same time also power the AC. So fuel consumption does go up.
Are you sure on this, i have tried this and see there is no increase in engine RPM audibly not except for fan kicking in but the needle does not budge beyond 900-950 rpm.

There may be possibility where alternator is supplying the additional current needed which we call engine getting robbed the power ?

One noob doubt here, will the compressor be spinning always as it is connected with the main transmission belt. what about models with ACC, i hear a distinct click when i hit the a/c knob, in the ACC model.
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Old 10th June 2014, 23:04   #114
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Default Re: A/C and fuel economy & How to use aircon optimally.

While driving between Bangalore and Chennai in GQ, I usually maintain 100Km/hr with rpm as 2750 in my i10 with 100% AC. If I want to speed up further, I'll switch off the AC to reduce the burden on engine. Also, rpm beyond 3000 reduces the FE from 19 to 17.
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Old 11th June 2014, 17:38   #115
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Default Re: A/C and fuel economy & How to use aircon optimally.

Quote:
Originally Posted by sriramr9 View Post
Are you sure on this, i have tried this and see there is no increase in engine RPM audibly not except for fan kicking in but the needle does not budge beyond 900-950 rpm.

There may be possibility where alternator is supplying the additional current needed which we call engine getting robbed the power ?

One noob doubt here, will the compressor be spinning always as it is connected with the main transmission belt. what about models with ACC, i hear a distinct click when i hit the a/c knob, in the ACC model.
. In all my Marutis, the idling with AC is higher than idling without. There is a small relay which is activated when AC is on and it opens up the throttle a bit.

. The AC pulley is always rotating when the engine is, but the AC is not. When you switch on the AC, a clutch in the AC is activated and connects the input to the AC main shaft. That is the click you normally hear when switching the AC on.

. The so called temperature knob is basically a mixer for the heater. At extreme blue the heater is off, and as you keep moving towards red the heater get more and more hot. Note that the heater is nothing but a pipe from the radiator supplying hot water, and has its own mechanical controller which determines how much hot water is to be let in.

. In my older M800, there was a thermostat similar to that of domestic AC, and that would control the temperature. In the newer model that seems to be missing.
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Old 15th June 2014, 12:09   #116
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Default Re: A/C and fuel economy & How to use aircon optimally.

Quote:
Originally Posted by Aroy View Post
.
. The so called temperature knob is basically a mixer for the heater. At extreme blue the heater is off, and as you keep moving towards red the heater get more and more hot.
I am starting to believe this now and feel like a fool to have kept the knob in non-blue area ever! Do you think that even within the blue area (25% of knob movement for Swift), the heater would be ON at the lower cooling position? I have noticed the heater turns ON only after the 25% postion mark when the AC is off. This would mean one should always keep the knob at the highest cooling position.

Quote:
Originally Posted by Aroy View Post
.
. In my older M800, there was a thermostat similar to that of domestic AC, and that would control the temperature. In the newer model that seems to be missing.
In my Zen 2005, I could feel the compressor turning on and off if the temp was not set at max cooling. It was possible because the engine took a lot of load when the compressor turned on.
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