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View Poll Results: How long do you wait to switch on the AC in your car during a cold start ?
Immediately on starting 52 22.51%
1-2 Mins after start 92 39.83%
4-5 Mins after start 71 30.74%
10 or more Mins after start 16 6.93%
Voters: 231. You may not vote on this poll

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Old 5th February 2007, 16:31   #91
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I do not use the airconditioner too often. I love to drive with the windows rolled down. But, when I do use the AC, I start it about 30 seconds after starting the engine. So, I voted for the first option.
A "technical expert" at Sai Service advised me to switch on the AC 5 minutes after the engine is started and switch it off 5 minutes before the engine is switched off.
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Old 5th February 2007, 16:37   #92
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Hey.. I've a simple solution for people who have to use the AC at cold start (and, love your car, because the solution is kinda asking too much from you).

Take a bottle of water with you when you leave from home. Bathe your baby with the water and lower the metal body temperature and then, use the AC. This will sure help it get cold quicker and will put lesser strain on the engine.

Remember people used to have grass-bedding sorta thing on the top of their cars, and would wet it in the summers, about a decade ago, when AC wasn't fitted in all the cars? Why not use that old simple trick?
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Old 6th February 2007, 11:11   #93
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@amu1983. good suggestion, but its gonna make your baby look sick with the water mixing with the dust.
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Old 6th February 2007, 12:01   #94
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Drive the vehicle for about a kilometre the first thing in the morning with windows rolled down. All parts shall be lubricated properly, hot air trapped inside shall be sucked out and engine shall also warm up. Then switch on the AC.

As the old saying goes: "No gain without pain"..
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Old 6th February 2007, 14:19   #95
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Switch the AC after the engine reaches optimum temperature...which is usually in about 3-4 minutes, same holds good for revving the engine, always wait for the optimum operating temperature.
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Old 6th February 2007, 14:36   #96
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Whats the logic in all this.
I understand why we shouldn't rev the engine.
But how much load does an AC actually put.
Lets see 100bhp engine.
Lets say AC takes 3BHP(this figure is way too high as room 1.5Tonne AC takes 2BHP(1.5KW)
So 3% more load. Slight revving up will lead to this much load.
Can anyone explain to me the logic of "letting engine warmed up blah blah)?
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Old 6th February 2007, 16:40   #97
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Quote:
Originally Posted by tsk1979 View Post
Whats the logic in all this.
I understand why we shouldn't rev the engine.
But how much load does an AC actually put.
Lets see 100bhp engine.
Lets say AC takes 3BHP(this figure is way too high as room 1.5Tonne AC takes 2BHP(1.5KW)
So 3% more load. Slight revving up will lead to this much load.
Can anyone explain to me the logic of "letting engine warmed up blah blah)?
I had asked same question in this thread back in September link

But got no satisfactory answer.
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Old 6th February 2007, 16:43   #98
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I guess then people are just giving "gyan" without knowing at all what they are talking about .
IMHO, 3% load on the engine should not be of any problem. If you slot your car in gear and slowly move off even that will put a much higher load on the engine than just the air conditioning.
The 3BHP figure I quoted is on higher side, we don't really have a very powerful AC like the room AC, so 1-1.5KW would be more like it.
In case of a car like M800 the AC could be equivalent to 6-8% load but in most other cars putting above 50BHP this would translate to less than 5%.
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Old 6th February 2007, 17:20   #99
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Quote:
Originally Posted by tsk1979 View Post
Lets see 100bhp engine.
Lets say AC takes 3BHP(this figure is way too high as room 1.5Tonne AC takes 2BHP(1.5KW)
So 3% more load. Slight revving up will lead to this much load.
Any engine deveopes its max power at a certain rpm which is certainly not its idling/starting rpm. This 500 hp engine developes just about 70hp at 1250rpm!

So.. the 100bhp engine would probably be developing about 15-20bhp at idling.
Wont' adding 3bhp a big overload?

Last edited by k36 : 6th February 2007 at 17:21.
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Old 6th February 2007, 17:24   #100
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Well if you start moving the car it is going to put much more load.
When we talk about not running the car at high rpm for first few minutes it means do not utilize full power initially.
With 3bhp increase we are still nowhere close to utilizing full power.
By this logic cars should idle for 5 minutes before even starting off, because when we go to 1500rpm its like 20-30hp more from the engine!
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Old 6th February 2007, 18:55   #101
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Quote:
Originally Posted by tsk1979 View Post
Whats the logic in all this.
I understand why we shouldn't rev the engine.
But how much load does an AC actually put.
Lets see 100bhp engine.
Lets say AC takes 3BHP(this figure is way too high as room 1.5Tonne AC takes 2BHP(1.5KW)
So 3% more load. Slight revving up will lead to this much load.
Can anyone explain to me the logic of "letting engine warmed up blah blah)?
I don't think the pieces are fitting together. I have a couple of doubts

Why would one feel a drop in performance if A/C takes only 2-3% of the total developed BHP ?

In my personal experience fan speeds above 3 on Petra causes a drop in performance, where as fan at position 2 or 3 really does not cause any perceivable loss. Observed similar or worse loss of performance in Balenos, Accents, Ikons and Esteems too.

The performance drop to my gut feel is definitely more than 2-3%. It definitely does not feel marginal in the mid range too. Only at the high end it may be. At low end it feels more like 20-30% drop. Do we have to add the load created by both A/C and distribution system ?
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Old 6th February 2007, 18:58   #102
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K36 makes a great point. It also has to with torque charactersitcs of the engine. In a diesel engine, I would say the AC would hardly make a difference even in idle. On my OHC, I can certainly feel the load on the engine at low engine revs with the AC on.
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Old 6th February 2007, 20:19   #103
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Quote:
Originally Posted by Floyd de Souza View Post
Thanks SB...I too do the same as you i.e. keep the TC knob in the white area just before the red zone but that mechanic claimed that FE could drop by around 0.5kmpl by doing this. 0.1 or 0.2 kmpl difference can be digested but a 0.5kmpl difference is difficult to ignore.
I don't agree. when you keep it anywhere oher than full COLD, but towards cold, I don't think any hot air will come in to mix with the cold air. hot air comes in only when you move the temp control towards HOT.

keeping it switching on and off to maintain optimum temperature is same as keeping the temp control at optimum setting. the themostat takes care of what you have been doing manually.

I don't think this will lead to EXTRA fuel consumption than what you have been practising, in fact, your compressor is doing sudden stops and starts which may not be desirable.

I think the things that is confusing us is teh temp control knob.

1. Is it just to divert the hot/cold air into the cabin?
2. Or, is it related to thermostat, to control the temperature, like in home ACs.

And if it's the first case, remember that energy required to cool a cold object (shifting heat from cold temp to hot temp) is much more than energy required to cool a hot object (shifting heat from hot temp to cold temp, which is spontaneous)

he he he, confused you even more.
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Old 7th February 2007, 10:14   #104
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Quote:
Originally Posted by vivekiny2k
I don't agree. when you keep it anywhere oher than full COLD, but towards cold, I don't think any hot air will come in to mix with the cold air. hot air comes in only when you move the temp control towards HOT.
Well, as per MUL literature, hot air does mix with the blower air when the temp knob is at any setting other than the "full cold" setting.
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Old 7th February 2007, 11:09   #105
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Quote:
Originally Posted by vivekiny2k View Post
I don't agree. when you keep it anywhere oher than full COLD, but towards cold, I don't think any hot air will come in to mix with the cold air. hot air comes in only when you move the temp control towards HOT.

keeping it switching on and off to maintain optimum temperature is same as keeping the temp control at optimum setting. the themostat takes care of what you have been doing manually.
That's not the case, please try the following: While keeping the AC OFF (manually) adjust the temp-control knob within the cold-neutral range. You will notice the change in air temperature as you move from cold towards neutral. What, other that hot air mixing, can cause this?
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