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Old 19th April 2007, 04:00   #16
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rohitbhai, that was a very good way of explaining operation of aircon system in non climate control cars. the purpose of this thread was to confirm this fact & I want to DIY a temperature control system.
can somebody design a circuit or give basic idea with a thermistor , a relay& a variable resistor like a volume control knob.I plan to disconnect the original thermostat & put a relay in circuit. a thermistor will take place of thermostat. when I vary the variable resistor I must be able to change the thermistor operating value. a separate thermometer at the grill will tell the actual temperature output. I think default grill temperature is 11. if I can vary this from 5 to 25 it will solve the problem & maximize FE. a multi pole switch may replace the variable resistor once exact value of each setting is found out.
I hope I am explaining my project properly.
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Old 20th April 2007, 19:01   #17
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i think we have a shortage of DIY guys in teambhp
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Old 21st April 2007, 16:51   #18
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Hello guys,

I have a question about AC in M-800. In our M-800, I have observed that the compressor trips very often when the blower is in position 1. It trips every 30 seconds even in the sweltering heat in the afternoon when there is no cooling at all and passengers are sweating profusely. Ideally, considering the amount of cooling of the 800's AC, shouldn't the compressor be on all the time?

Can some of the experts please explain this phenomenon?
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Old 21st April 2007, 21:30   #19
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akmar, get your ac ducting below bashboard checked for leaks. check the thermostat, if faulty replace it with aftermarket ones available for 250rs max. ask the installer to lower the grill temp to 6(4 if compressor can handle it), be ready to loose mileage due to this mod. delhi heat is real difficult to handle
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Old 31st October 2011, 21:58   #20
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Default Re: Airconditioning cars, were we fooled?

Sorry for Digging such a OLD Topic. But I could not stop myself from posting under this topic.

When the AC is Turned ON, it will Cool the Cabin and the Compressor Cuts Off automatically. So there is in fact no need to Switch Off the AC Manually.

If the procedure of MANUALLY Turning AC ON and OFF every few mins is followed, it will waste more fuel.

I will explain both cases of-
1) Keeping the Temp Knob at Coldest (Blue Zone) Position and turning the AC manually OFF when the cabin has cooled and ON when the cabin has become hot.
If AC is Manually switched OFF after cooling and again Turned ON when feeling hot, the Compressor will have to cool the entire cabin over again which will waste fuel.

2) Keeping the Temp Knob at Near Middle Position and the let the AC compressor do its work.
If the AC Temp. Knob is kept at near middle position, it will Cool the Cabin to the Temp. corresponding to that Knob Position and the Compressor Cuts Off automatically. Remember this Temp. is more than that of Temp. when AC Temp. knob is at Coldest (Blue) Zone. So the Compressor cuts off early (since the Pre-set Temp is reached earlier) and since the Compressor does not have to cool the entire cabin again (to the Minimum Temp), it will save fuel.

I will explain with an Example.

1)Case 1- AC Temp Knob kept on Blue Zone (Coldest)
Lets assume that the AC Compressor Cools the cabin to 18 Deg C at this setting--
When the AC is Turned ON, it will Cool the Cabin to 18 Deg C and the Compressor Cuts Off automatically. Now if AC is Manually switched Off and again Turned On when feeling hot (temp. may have risen to @ 25 Deg C), the Compressor will have to cool the entire cabin over again to 18 Deg which is 7 less than that of Current (read Hot) Temp. and this will waste more fuel.

2) Case 2- AC Temp Knob kept at Near Middle Position
Lets assume that the AC Compressor Cools the cabin to 22 Deg C at this setting--
When the AC is Turned ON, it will Cool the Cabin to 22 Deg C and the Compressor Cuts Off automatically. Now the Compressor Turns ON when feeling hot (temp. may have risen to @ 25 Deg C), the Compressor will have to cool the cabin just 3 Deg as against to 7 Deg in Case 1.

EDIT: -
Also when the AC Temp Knob is kept at Near Middle Position, as the Hot Air from Engine is mixed with Cold Air from Compressorto achieve the Pre-set Temp, the Engine Temp gets somewhat (not drastically) reduced.

Last edited by IndigoXLGrandDi : 31st October 2011 at 22:07.
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Old 31st October 2011, 22:29   #21
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Default Re: Airconditioning cars, were we fooled?

^^^
???. To everything.

Off topic:
The water heater in your bathroom -
On all the time, thermostat doing its work, or
switched on half an before your bath, and then switched off.

Relative electricity consumption in the two scenarios?

Regards
Sutripta
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Old 31st October 2011, 22:51   #22
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Default Re: Airconditioning cars, were we fooled?

Quote:
Originally Posted by IndigoXLGrandDi View Post
Sorry for Digging such a OLD Topic. But I could not stop myself from posting under this topic.

When the AC is Turned ON, it will Cool the Cabin and the Compressor Cuts Off automatically. So there is in fact no need to Switch Off the AC Manually.

If the procedure of MANUALLY Turning AC ON and OFF every few mins is followed, it will waste more fuel.

I w.
.
.
.
.<snip>
.
.

EDIT: -
Also when the AC Temp Knob is kept at Near Middle Position, as the Hot Air from Engine is mixed with Cold Air from Compressorto achieve the Pre-set Temp, the Engine Temp gets somewhat (not drastically) reduced.
Whatever you have said is wrong.
In modern cars with climate control, hot air is mixed with cold air to regulate cooling.
In most cars below 10L, there is no climate control, but a "mixer" knob. IT tells how much hot air is to be mixed with cold air.
So if you keep it at middle, it will just mix cold and hot air, and give out cool air instead of air at 5 degree C(or whetever is the grill temp).

Last edited by tsk1979 : 1st November 2011 at 12:18.
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Old 31st October 2011, 23:56   #23
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Default Re: Airconditioning cars, were we fooled?

Those who are familiar to JavaRanch, a forum for everything related to Java might remember the phrase "don't wake the zombies" for digging up an old post. But, I feel it is good by Team-BHP to leave this post open and do not mind waking up a zombie, because, the topic of this thread never became old.

Quote:
In modern cars with climate control, hot air is mixed with cold air to regulate cooling.
I thought, with automatic climate control, there is a sensor to measure inside car temperature. Once the interiors have become cold enough to the set temperature, wont the compressor get cut off? In this regard, setting a temperature of 16 degree would keep on making the compressor and the fan work till it reaches 16. Assuming an outside temperature of 24 degree, an automatic setting of 22 degree would free up the compressor much early than the 16 degree setting (even if the mixing of hot air may be needed for the 22 degree setting).

Assuming that I am correct above, I doubt what happens if we do not use the automatic climate control, but still set the temperature to 22 degree? Will the compressor get cut after reaching the set temperature? Or will it still keep on mixing hot air with the cold air without cutting off the compressor?
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Old 1st November 2011, 08:14   #24
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Default Re: Airconditioning cars, were we fooled?

Most Car A/C's have a thermister set around 2.5~4 dec Celsius near the grill. When the grill temp reaches the desired temperature it simply cutoff the compressor. It will not sense the cabin temperature. Once the evaporator loses it chill due to heat exchange the compressor starts again. Thats the reason if you want good FE keep the blower fan to 1. When I asked the same to the mechanic he told me higher blower fan speed puts load on alternator hence less FE. Some part of is statement is true but 80% of FE is lost to the compressor load rather than alternator load.
Ideal A/C setup: Instead of mechanically coupling the compressor, ideal way would be coupling with brushless DC motor to get the variable refregrant flow, sensors inside the cabin to control the flow. The compressor will never turn off and keeps consistant cooling. What makes manufacturers not to try this method just like electric radiator motors.
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Old 1st November 2011, 15:24   #25
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Default Re: Airconditioning cars, were we fooled?

Quote:
Originally Posted by IndigoXLGrandDi View Post
If the procedure of MANUALLY Turning AC ON and OFF every few mins is followed, it will waste more fuel.

I will explain both cases of-
I'm sorry I do not understand.

I think you are mixing up Automatic climate control, and Manual AC. In a manual AC, if you manually control the compressor there is **absolutely** no fuel wastage, when compared to when its fully turned ON.
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Old 6th November 2011, 11:19   #26
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Default Re: Airconditioning cars, were we fooled?

Quote:
Originally Posted by tsk1979
In modern cars with climate control, hot air is mixed with cold air to regulate cooling.
In most cars below 10L, there is no climate control, but a "mixer" knob. IT tells how much hot air is to be mixed with cold air.
The function which the Climate Control does in a Climate-Control-Equipped Car is performed by Temp Knob in a Non-Climate-Control-Equipped Car.
If the AC Temp Knob is kept on Coldest Position, how come the Compressor mix Cold Air with Hot Air.
It does mix Cold Air with Hot Air when the Temp Knob is kept near middle position.
Quote:
Originally Posted by tsk1979
So if you keep it at middle, it will just mix cold and hot air, and give out cool air instead of air at 5 degree C(or whatever is the grill temp).
Due to keeping the Temp Knob at near Middle Position, the Temp to which the cabin is to be cooled is higher and hence the Compressor does not have to work very hard as compared to when the Temp Knob is kept at Coldest Position. Please see my examples. The Difference of Temp to cool varies between 3-7 Deg C.



Quote:
Originally Posted by dhanushs
In a manual AC, if you manually control the compressor there is **absolutely** no fuel wastage, when compared to when its fully turned ON.
The Compressor cuts Off & Turns On every few mins and Does Not Remain Permanently ON Even If the AC Switch Is In ON Position. Hence when the Compressor cuts off, IT Does not SAP Power From Engine.



Please have a look at below pics--
1) The AC Temp Knob of Indigo XL Grand DiCOR has Blue Zone till Halfway and Red Zone below that.
Airconditioning cars, were we fooled?-dsc01689.jpg

2) In Indigo LS IDI (not TDI), the Blue Zone goes on decreasing as the AC Temp Knob is Turned towards Red Zone and Vice-Versa for Red Zone.
Airconditioning cars, were we fooled?-dsc01692.jpg
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Old 6th November 2011, 11:49   #27
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Default Re: Airconditioning cars, were we fooled?

Quote:
Originally Posted by IndigoXLGrandDi View Post
The Compressor cuts Off & Turns On every few mins and Does Not Remain Permanently ON Even If the AC Switch Is In ON Position. Hence when the Compressor cuts off, IT Does not SAP Power From Engine.
A known fact. You can even hear the relay clicking when the compressor turns on and off. But how does that translate into better FE? Whats the difference in switching it off and on manually?




Quote:
Originally Posted by IndigoXLGrandDi View Post
If the procedure of MANUALLY Turning AC ON and OFF every few mins is followed, it will waste more fuel.
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Old 6th November 2011, 12:21   #28
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Default Re: Airconditioning cars, were we fooled?

Where are variable displacement compressors used?

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Old 6th November 2011, 13:10   #29
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Default Re: Airconditioning cars, were we fooled?

I really doubt if the compressor really is switched off with Automatic Climate control system, even in the winters when AC button is on and no cooling is required i have observed the compressor is always switched on, even the ACC uses mixing to achieve the set temperature. This comes with my experience with Climate control systems of Elantra, Punto and Fortuner.

My Laura does not have ACC but it has variable load compressor, the effects of load can be seen on live Fuel consumption display. On a hot afternoon with AC set on 22(yes, the thermostat knob is marked with temp) the display shows close to 1litre/hour at idle, with the same settings the consumption drops down to as low as 0.6litre/hour when not much cooling is required. BTW i keep the knob fixed at 22 with AC on all the year round and i do not miss Climate control at all, all extra it can do is regulate fan speed automatically and change air flow modes.

Last edited by .anshuman : 6th November 2011 at 13:11.
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Old 6th November 2011, 13:47   #30
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Default Re: Airconditioning cars, were we fooled?

When we talk about fuel consumption and lower FE when the AC is on, what kind of FE saving are we talking about here, really? A 0.5 km extra? Or a whole 1 km extra with every liter?

Someone mentioned that the cabin would get warm and the compressor will have to work double-time to cool the cabin, if the AC is repeatedly switched-off. So I've noticed that my Santro gives me about 10.5 in the city with the AC switched on occasionally. And it will give me 11.5-12 if driven without the AC turned-on and if I drive with a really light foot.

When there are decimal points involved, I generally try and stay out of it, because I find it a little silly.

It's like conversations that happen when the topic is about tyres. A slightly wider contact-patch or a lower profile might increase FE. Really? Sigh.
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