air conditioning and fuel economy

Submitted: Monday, Feb 23, 2004 at 19:51
ThreadID: 10735 Views:1677 Replies:10 FollowUps:10
This Thread has been Archived
Howdy folk

Just a quickie, if I have my air conditioning temperature level turned down so it is not totall turned to cold, does this mean that the compressor etc is working less so the vehicle will not use as much diesel? Or does the compressor work just as hard when you have the heat turned right up (like when defrosting windows) as when you have it on very cold? Hope this makes sense!
(1999 Jackaroo TD manual if it makes any difference?)
Just interested because if it makes no difference may as well enjoy freezing conditions on a 40 degree day.

Regards

D-Jack
Back Expand Un-Read 0 Moderator

Reply By: simon - Monday, Feb 23, 2004 at 19:57

Monday, Feb 23, 2004 at 19:57
?

You have a diesel jackeroo if thats not good enough enconomy might want to look at a charade or one of the new smart cars.
Just push the button dont worry about the extra 10cents per 100km and enjoy the cool air you only live once may as well make the most of it.

(dad is that you)
AnswerID: 47764

Reply By: Wayne (NSW) - Monday, Feb 23, 2004 at 20:05

Monday, Feb 23, 2004 at 20:05
Once the cltuch is engaged the compressor is working. The thermostat which is pre-set will turn the unit off and on.I would think get the inside of the vehicle down to the thermostat temp, and the unit will not have to work as often.

The amount of extra fuel you might use running the air con would be a small. Slowing down 5klm per hour will safe fuel but you will take longer to get to where you are going. You have paid for the air con so use it.

WayneAlways Out'N About
AnswerID: 47766

Reply By: Matt M - Monday, Feb 23, 2004 at 20:53

Monday, Feb 23, 2004 at 20:53
DJack, if the air con is on and the thermostat is on anything other than cold, your aircon system will work harder, it has to cool the air from the heater. Good if its for defrosting but not if you want cool air.

Not a big deal but if you have it on and its too cold then turn it down or off, the compressor will have to compete witht hte heater and yes it will work harder than it should have to!

Hope that answers your question.

Matt.
AnswerID: 47781

Follow Up By: donk - Monday, Feb 23, 2004 at 21:48

Monday, Feb 23, 2004 at 21:48
Mattt

I think you will find that the air goes through the aircond evaporator & is cooled before the heated air is added by the air mix door when you have the temp control on anywhere other than the lowest cold setting
Therefore the aircond is not working any harder when a hotter setting is selected

Regards Don
0
FollowupID: 309744

Follow Up By: Matt M - Tuesday, Feb 24, 2004 at 18:01

Tuesday, Feb 24, 2004 at 18:01
Djack, I stand by my first statement, if the thermostat is on anything other than cold, then the air con will have to work a little harder. Whether that is noticable or not is prob not, but that depends on the how hot you have the thermostat set. So DJack if you are worried about how hard it is for the aircon to cool, why would you introduce more heat into it, making it work harder. The air you spent that energy cooling would then start being heated again..I dont get why you would want to unless on the lowest setting the air is too cold for you. If so I wish my system had that problem!!

donkkk,

Please if you have no idea on what you are posting about, then just DONT! Save people being mislead with wrong information. I cant be bothered going to go into the workings of the cooling/heater intake system for you to understand, get a book and learn for your self and you will see your error. But I will mention one point and hopefully that will be all you need.
If you are trying to cool a car interior and the cool air is being mixed with hot air (no matter where we mix it) then the cooling system will have to work harder to cool the vehicle. YES!! I dont see what part of that is hard to understand. Goodluck with quality helpful posts in the future.
Matt.
0
FollowupID: 309836

Follow Up By: TOB - Tuesday, Feb 24, 2004 at 18:55

Tuesday, Feb 24, 2004 at 18:55
You are all on the wrong track through 1 basic mistake, i think.
If the car has thermo control for the air con this will affect the amount times the compressor cuts in. However in a normal situation when you turn the air on it will pump cold air from the compressor until it starts to freeze. At this stage the condensor cuts out the compressor to stop it freezing. This will happen reguardless of the temperature inside the car.
By adjusting the temp in the car it simply blows warm air from the heater core and this mixes with the cold air from the air/con. it has no affect whatso ever on the air con compressor. If you are to tight to use the aircon you mat as well disconnect the aircon belt and you will get slightly better fuel economy.
I have had a condensor fail which did not kick in to stop the compressor.
I kid you not, it snowed in my car and you could freeze to death on a 40deg day

TOB
0
FollowupID: 309852

Follow Up By: donk - Tuesday, Feb 24, 2004 at 21:36

Tuesday, Feb 24, 2004 at 21:36
Matt

I do actually have a fair idea what i am talking about (i used to fit airconds to toyota's for a living)

In a toyota (with the vent fresh/recirc control on fresh) the air is drawn from the outside & then goes through the fan housing then through the
evaporator & is cooled (actually the heat is extracted) then it goes past the heater where heat is added if the temp control lever is anywhere other than the full cold position and then it comes out of the vents at the desired temperature

In your original post i believe you said that the air went through the heater core first & therefore if you were putting heated air through a evaporator the thermistor would keep the compressor operating for a longer period of time

With the fresh/recirc in the fresh position the compressor will operate for the same amount of time (within reason) regardless of where the temp control is because it is being controlled by the airflow before any heated air is added.

Regards Don

0
FollowupID: 309876

Follow Up By: Matt M - Wednesday, Feb 25, 2004 at 20:26

Wednesday, Feb 25, 2004 at 20:26
Don
OK last post, this is stupid. If you your aim is to cool the interior of the car and you introduce heat into it, the air con works harder. The thermostat controls the aircon compressor, so if you are drawing heated air from the cab, its going to work harder!
I believe I said the aircon has to cool air that is heated (see above), nothing to do with were the heater lays in relation to the evaporator but I see your mistake.
I would expect someone with as much experience with aircon systems would see how obvious the origional question and answer was. Just reassures me as to why I dont take my car to Toyota!!
0
FollowupID: 309996

Follow Up By: donk - Wednesday, Feb 25, 2004 at 21:45

Wednesday, Feb 25, 2004 at 21:45
Matt

This was the original question

if I have my air conditioning temperature level turned down so it is not totall turned to cold, does this mean that the compressor etc is working less so the vehicle will not use as much diesel? Or does the compressor work just as hard when you have the heat turned right up (like when defrosting windows) as when you have it on very cold? Hope this makes sense!


My answer as i have said in my 2 posts is based on the fresh/recirc control being in the fresh position where the air that is coming past the evaporator core(where the thermister is located) is from outside (not heated) & therefore the thermister will be cycling the compressor on and off at the same intervals (regardless of the heater control position & assuming the heater is located after the evaporator)to maintain the desired temp (39 degrees fahrenheit) at the evaporator core for the optimum operation of the airconditioner
From your continued reference to the airconditioner having to work harder due to the air flow past the evaporator being heated at first i assumed you believed the evaporator was after the heater core but on now i am you are assuming the fresh/recirc control is on recirc & this would be correct
I am sorry if i offended you in my first post as this was not my intention & i forgive you for your rude & offensive response to my first post

Regards Don
0
FollowupID: 310029

Reply By: Member - Cocka - Monday, Feb 23, 2004 at 21:05

Monday, Feb 23, 2004 at 21:05
If you were running short on fuel in a desperate situation or wanted a teensy bit more power or engine was overheating then shut it off, otherwise enjoy the comfort it was designed to give. When touring I often shut mine off and wind down the window just to get the sweet smell of the country in my nostrils.

If you want to check the little amount of power it consumes, with the engine ideling, just watch the tacho and turn air con switch on/off. Otherwise, with a steady foot on the go pedal whilst going up hill turn the air con off, I don't think you'll get your head ripped off with any extra surge in power.
Recycling the internal air helps to keep the unit from working continuously also, but not much, depends on the ambient temp.Carpe Diem
AnswerID: 47783

Follow Up By: Wayne (NSW) - Monday, Feb 23, 2004 at 21:13

Monday, Feb 23, 2004 at 21:13
Recycling the internal air is a good way to send the driver to sleep. I would rather breath warm fresh air than cold recycled CO2.

Wayne Always Out'N About
0
FollowupID: 309733

Reply By: Bazza - Tuesday, Feb 24, 2004 at 08:53

Tuesday, Feb 24, 2004 at 08:53
G'day D-Jack,
I think your question has been answered by others, but ... no offence intended ... IMO I find it hard to believe that anyone should be concerned with the fuel economy, diesel or petrol, on medium to large 4B's. If it is a concern ... I think you may be driving the wrong vehicle.
Regards,
Bazza.
AnswerID: 47829

Reply By: Rick Blaine - Tuesday, Feb 24, 2004 at 08:56

Tuesday, Feb 24, 2004 at 08:56
As an owner of a T/D Jack I have done some practical work on economy... when I'm not in an arguement with Holden over poor service.

Whether or not I have aircon on for a trip of 100 km means very little cost wise about 36 cents with air on. If I do the same trip with the windows down then it costs an extra $1.17 cents!!!!! Using the heater in winter makes no difference to fuel costs.

My only real advice is to make sure you give the aircon a short run... say once a week ... in winter to keep the seals lubed.

AnswerID: 47830

Reply By: jackablue - Tuesday, Feb 24, 2004 at 09:16

Tuesday, Feb 24, 2004 at 09:16
On my petrol jack on the weekend the difference was 2lts per hundred with the a/c on full bore. 84 kms difference.
AnswerID: 47832

Reply By: jeff-wa - Tuesday, Feb 24, 2004 at 13:42

Tuesday, Feb 24, 2004 at 13:42
You will find the compressor cuts in and out and the same rate so your will have the same economy. My ol' Rocky was great it actually had a thermostate style control instead of a simple on/off switch. It would change the cut in and out times of the compressor, fanstic idea and SO simple. My surf chews juice with the air con on and it's always bloody freezing! So I end up having to put the heater up a bit and just throw away those extra few cents! ;-)
AnswerID: 47868

Follow Up By: Matt M - Tuesday, Feb 24, 2004 at 17:49

Tuesday, Feb 24, 2004 at 17:49
Jef, you will find the Surf will either have a thermistor or a thermostat too, just not one you can easily adjust. It souldnt be too cold all the time, the cut in and out temps are pretty standard across the board for aircon systems. If it is too cold on the low setting, you might want to get it checked, but I sure wish I had that problem!

Matt.
0
FollowupID: 309834

Follow Up By: jeff-wa - Tuesday, Feb 24, 2004 at 18:09

Tuesday, Feb 24, 2004 at 18:09
It's great on those 40c days, the only thing is the motor tends to get a bit hot and bothered in the sand, so you might be right, may be running too much. I've got the radiator out today getting re-cored and a new top tank (has some pinhole leaks, not serious yet but would become bad news if not attended to) so hopefully that will solve my prob. Might leave the aircon as it is though, I like my hands going numb on those hot days! :-) I will get onto the guys on the Surf groups and see how easy it is to change, maybe worthwhile changing the settings between summer and winter?
0
FollowupID: 309839

Follow Up By: Matt M - Tuesday, Feb 24, 2004 at 18:28

Tuesday, Feb 24, 2004 at 18:28
OK Jeff, the thermistor is a replacement of old thermostats, its a tine electronic thermostat and is not adjustable, if the compressor isnt cuttin in at about 6deg and out at 3deg then the themisitor is us and its a throwaway. If you have the thermostat the gap between cut in and out are the same, but you can swing them up and down the scale slighly. Bare in mind, that if the evaporator runs lower than the 3degs(ish) it will start to freeze and then you lose you cooling due to loss of air flow across it! Great hey!! I would definately get those radiator hole fixed ASAP, Surfs are not renowned for liking hot work and overheating is one of their common downfalls, why make it worse when you know it needs to be fixed.
Goodluck with it.
Matt.
0
FollowupID: 309841

Reply By: Shaker - Tuesday, Feb 24, 2004 at 19:28

Tuesday, Feb 24, 2004 at 19:28
If you wind your windows down, you are upsetting the vehicles aerodynamics..... consequently using more fuel. There is minimal difference in economy between driving with the air cond on, or driving with the windows down! This was proven a few years ago after testing by the Ford Motor Co.
AnswerID: 47925

Reply By: D-Jack - Tuesday, Feb 24, 2004 at 21:43

Tuesday, Feb 24, 2004 at 21:43
Thanks guys for your replies - sorts it out in my mind - everything from no difference to 2l/100km difference!! Was not interested in finding out because I was having some sort of nervous breakdown about it though - just because I enjoy getting the most out of my vehicle - power/performance/economy - kind of an interest if you like. What's the point of using more fuel that you need to if you could turn the dial 15 degrees and still be comfortable?

P.S. Anyone interested in tagging along with me (with a mate in my vehicle) on 19/3/04 for about a week targetting 60lb + Mulloway/shark/snapper/yellowtail kingfish etc from Fowlers bay though to Yalata Aboriginal Lands? (an Aboriginal Aid at Yalata recently caught a 116lb Mulloway - the biggest ever recorded there! Tides/Moon is all perfect, just waiting for weather forecast!!

D-Jack

AnswerID: 47945

Sponsored Links

Popular Products (13)