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Old 6th June 2013, 19:51   #61
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Default Re: Airconditioning cars, were we fooled?

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Originally Posted by saket77 View Post
I would like to ask that does the blower speed matter when it comes to the extra load put on the engine by turning on the a/c or even fuel consumption?

For example, will it matter if I am using the A/C with blower on the first speed setting? And will shifting to setting 3 (or whatever is highest speed of the blowr in that particular car) will change the compressor behaviour/ engine load/ or affect FE of the car?

I would be interested in the answers in the the perspective of both newer and older cars, if they are different.

Also, my presumption is that when using only the blower or even the heater (without switching on the compressor) does not affects the FE & performance of the car, unlike A/Cs. Please share your knowledge on this too.

Thanks & regards,
Saket

As a general rule, switching on anything electrical puts a higher load on the engine. That goes for a fan or even your lights. Also switching your fan to a higher setting puts a higher load on the engine. Higher load due to electrical loading means you take a hit in the FE department. How much, well varies hugely. But on a medium sedan running the interior fan on full blast could easily cost you several kWs or HP's.

Normally the fan setting should not directly influence the compressor behavior.
Using your heater normally doesn't affect FE at all. What it means is that instead of running your coolant through the radiator cooled by air it is now running through a heat exchanger that warms up the air going in your car. Your engine doesn't know the difference. FE remains the same. There might be a few exceptional scenario's where FE might be affected, but they would be the exception rather then the rule.

My Jaguar has fully electronically controlled climate control, but my wife's little Fiesta, my Jeep Cherokee and my Alfa Romeo only has the on/off version. My Mercedes W123 doesn't have AC at all.

Rather than switching the compressor on and off, I find that it is often much better/convenient by just adding a little warm air. It does mean the compressor runs constantly, but it's designed to do so. Although the figures vary hugely between cars, running your AC could cost you 5-12% FE. On some cars when you use the kick down, the AC compressor gets disconnected as it makes a very noticeable difference on the acceleration.

Whether there is any difference in all of this between older and newer cars: You will find different answers if you google for this question. It's not so much the age of the car as what refrigerant was used. My 1986 Alfa Romeo Spider still uses Freon. Due to environmental concern the use of Freon has been virtually outlawed in most countries. No idea about India, but I assume it's the same here. New generation of refrigerants tend to have far superior thermodynamic properties. Although they work on higher pressures then the old freon system, the nett result is that the new systems are physically smaller, lighter, and use less power for the same cooling capacity.

To put it slightly different: Modern AC system (modern being post Freon) will have a positive effect on FE compared to the old freon based system. They are lighter, smaller and require less power to drive. Hence if everything remains equal you should have an uplift on the FE compared to Freon based AC equipped car.

Last little anorak fact: Running your AC with some hot air is the most efficient way of de-misting the inside of your windows as well. Especially in colder climates. The fully electronic climate controlled units do exactly this. If you have a on/off AC, just shove the warm air handle to full and put the fan on full blast and aim the air through the front window facing ducts.

Jeroen
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Old 7th June 2013, 10:06   #62
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Default Re: Airconditioning cars, were we fooled?

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Originally Posted by Jeroen View Post

Normally the fan setting should not directly influence the compressor behavior.
Using your heater normally doesn't affect FE at all.
Thanks Jeroen and EFF-EIGHT-BEE for your inputs. The quoted above two lines clears my doubt.

More than electrical load, I wanted to know if compressor puts more load on the running engine at a higher blower speed.
In fact this story stretches back to an year or so. I was sure that the blower speed does not affect engine performance & FE, but I a driver-cum-mechanic who was driving my uncle's Alto was boasting that how there is no drop in the performance of the car, even with the blower speed on max setting with the AC. I interrupted him saying that blower speed will not affect performance, but he insisted on his version till we reached our destination.

Thanks,
Saket
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Old 7th June 2013, 11:50   #63
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Default Re: Airconditioning cars, were we fooled?

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Originally Posted by saket77 View Post
More than electrical load, I wanted to know if compressor puts more load on the running engine at a higher blower speed.
The compressor puts a mechanical load, a higher blower speed will add electrical load. Impact is more with the compressor activation than higher blower speed. On some cars you feel the power drop during compressor activation. It could be felt even on a car like the Ikon 1.6l. I don't feel this though on my Fiat T Jet. You have no idea that the compressor has cut in or out. I know it has cut out as the radiator fan stops working momentarily when cabin temperature is achieved via set temperature on the climate control.
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Old 7th June 2013, 19:05   #64
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Default Re: Airconditioning cars, were we fooled?

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Originally Posted by saket77 View Post
More than electrical load, I wanted to know if compressor puts more load on the running engine at a higher blower speed.
Sandeephohan answer is correct. To put it simply, the answer is no.

Your AC compressor is running or not. Therefor it puts a certain load on the engine or not.

Your blower is running at a certain speed. That puts a certain loading on the engine. If you increase the blower speed it will put a higher loading on the engine.

So the compressor and the blower are independent of each other in terms of loading up the engine, but both can and do put a load on the engine.

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Old 7th June 2013, 21:50   #65
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Default Re: Airconditioning cars, were we fooled?

Quote:
Also switching your fan to a higher setting puts a higher load on the engine. Higher load due to electrical loading means you take a hit in the FE department. How much, well varies hugely. But on a medium sedan running the interior fan on full blast could easily cost you several kWs or HP's.
Strange it may seems but using fan in lower speed will put a bit higher load on battery/alternator. Reason being fan regulator uses resistors.


Quote:
So the compressor and the blower are independent of each other in terms of loading up the engine, but both can and do put a load on the engine.

Jeroen
Compressor will put more load as its directly driven by engine through belts. Cooling fan and blower a slight minimal load. Its driven by battery/alternator.

Unlike compressor alternator is always being driven by engine, whether you use its power to fullest or say 5%. There is no question of load unless you reach a threshold point at which your alternator or battery will heatup (Eg: while using electric winch) which is rare.

Take for example people are packing their cars with 10k rms watt of music system on 12volt battery for ages. Did it ever affect the driving conditions except for by standers who will curse you for that blarring what not playing on it.

Last edited by SirAlec : 7th June 2013 at 21:57.
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Old 7th June 2013, 21:52   #66
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Default Re: Airconditioning cars, were we fooled?

Thanks everyone who contributed.
My initial concept was correct, however, was put in useless doubt. The only reason that I believed the driver was because he was a mechanic too.
May be these posts should be moved to a thread that I faintly recall as something as 'most hilarious statements by non-petrolheads'. Thanks to teambhp that I personally don't feature as the central character in that thread!

Thanks,
Saket
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