Air Con and MPG

[un1eash]

Just a quick question that i was thinking about the other day. Having the air con on tends to use MPG in most cars, now what happens if you have the air con turned on but the heaters are blowing out hot air, does this still engage the air con and use MPG???

 

Reason i ask is my windows kept fogging up in this cold weather and it only went away if i turned the air con on, it seems pointless as i've got my heaters on hot.

[martinmac]

I am happy to be corrected but the aircon will remove the moisture from the car, with the roadster I have to run it for ages to dry it out.

[un1eash]

Does this use more fuel though like it would in the summer when your blasting ice cold air out?

[nzd31155]

Pasted from elswhere...

 

The air conditioner wastes more gasoline, hands down.

 

Turning the heater on uses heat energy all ready stored in your cars coolant system to warm the air in the cabin. This is why your heater does not work until the car has been running for a few minutes. This energy is all ready in the car if you use or or not.

 

The A/C on the other hand activates a compressor which requires more electricity from your cars alternator to run. The energy to power the compressor has to be converted by the alternator, making your motor work harder. Some cars also have an additional fan that turns on with the A/C to help keep the alternator cool as it too works harder. This fan also draws power though, creating an even greater load for your motor.

 

If you wanted to test this, let your car run for a minute or two until its at its normal idle RPM. When you click the A/C on you will most likely see the RPMs on the tach increase. This is your motor compensating for the additional work it is doing by increasing the rate at which it works (RPM).

 

Sorry for sounding like a science teacher, hope this helps and lets you shut your friend up =)

 

PS: Using the A/C will cause you to burn more fuel if your on the freeway or in the city, either way.

 

PSS: Often times, rolling your windows down will cause you to burn even more gas than using the A/C, at least while at freeway-speeds of 60+. This is because you are creating much more aerodynamic drag with the windows down. It depends a lot on the vehicle your in, but more often than not this is true.

[un1eash]

I thought the air con in modern cars was belt driven and when the air con is turned on it engages a clutch in the air con pump, this extra load causes the increase in mpg.

 

This is why i wasnt sure if having the air con on but not blowing cold engages the pump or not.

[Sam Mcgoo]

If the aircon is on , the pump is on. Temperature selection will make little or no difference to the load on the pump so will use just a much fuel....

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I think.

[Vik54]

Of course it uses more fuel - but you haven't got a choice driving the zed in the UK if you want to see where you're going

[spursmaddave]

Who cares about MPG anyway? If you do then buy a more economical car

 

I have the aircon on all year round whatever the weather and when it is cold like this I have the heated seat on too I probably burn a small part of the rain forest every trip to work but at least my arse is warm

[un1eash]

I dont care to much about mpg, i currently get 10mpg with an average speed of around 11mph. My question was more about if the air turns off by itself when not needed for cooling even if you have it switched on.

[spursmaddave]

I'm pretty sure the air con is on if it is blowing hot or cold... If it is cold or worse wet outside you have to have the air con on or its like a turkish bath! I also keep the rear demister on as that fogs up a bit too...

[cmck13]

If your air con is switched on it will cost, if your heater is switched on it will cost, the air con is dearer in mpg, the heater is cheaper.

If you use your heater you will wait an eternity for it to clear steamed up windows, if you use your your aircon it will do it in seconds because it recycles.

However I dont use both together, so after that I am as wise as you, check this link and if you find the answer let me know because I don't know any more.

 

http://www.airconcars.com/html/how_it_works.html

 

jeff

[Rx7Rebel]

Maybe try rainx antifog solution?

[GT4 Zed]

I read 350z US a while ago that on the zed the a/c on is worth <3mpg more and in the <5-7hp parasitic loss:surrender: so its not to bad overall. Mythbusters worked out that with windows down is better up to 55mph and worse thereafter but it means little as it all depends on the aero profile of the car. the zed as a good Cd so it may be worse due to more drag created with the windos down.

 

WRT to your excess fogging in your car I think you need to exclude other causes excessive moisture which is more likely than just cold ambient weather. I donot have any fogging issues once the initail mist has been cleared off

 

The prime culprits are:

- wet boot or floor mats from leaking rubber seals after rain or overzealous valet/car wash .

- user error :You should not recirculate the air but rather switch to refresh mode when its especially cool outside or when you notice the mist building. The middle dial controls this function which a simple press down and the light indicates either choice.

 

If you find no faults try to stop sweating alot or use antifog.

 

finally as already covered the ac is more efficient at removing mist than the heater that will take ages and the window down is likely worse on yuor mpg

[JetSet]

I read 350z US a while ago that on the zed the a/c on is worth <3mpg more and in the <5-7hp parasitic loss:surrender: so its not to bad overall. Mythbusters worked out that with windows down is better up to 55mph and worse thereafter but it means little as it all depends on the aero profile of the car. the zed as a good Cd so it may be worse due to more drag created with the windos down.

 

 

Yeah, 3mpg sounds about right as does the 7bhp loss. The percentage loss of mpg looks to be pretty constant over a range of cars. Power loss is much more obvious in cars with 60 or so bhp, rented a small Suzuki Swift? in Arizona and had to turn A/C off up a lot of hills as 60 ton trucks started passing me . On some cars A/C won't come on if the outside temp is less than 3 centigrade to prevent damage from icing, don't know if the Zed has this feature though .

 

Pete

[sasha@lazytrips]

I must be the only person who when placed next to an obnoxiously revving neighbour at traffic lights, who is trying to jump a queue of cars by going straight from a lane designed for right turns only, apart from all the other obvious necessary steps turns off the aircon, radio & heated seats in preparation...

[stanski]

I think we need to chill here - the aircon pumps from ye olden days were massive things akin to washing machine motors the newer stuff is far more efficient.

The Zed remember has a 3.5 Lt V6 - this has massive torque (like a diesel really)- it is not a Nissan Micra 1.0 engine. If you have the aircon on all the time then yes it will help to drink some of your petrol more so around town driving, on the motorway I not very much.

 

So dont worry too much about the aircon being on -it will hardly make that much difference to your fuel bill, well I never really noticed much difference when I had my ragtop and as Mart says Ragtop owners tend to fog up quicker than tintops.

In fact it was too damn efficent and I used to switch it off once the snowman appeared in the other seat!

[ATTAK Z]

Isn't the good life in general all about being comfortable ? If "aircon on" is better than "aircon not on" then go for it .......... if you can't afford it, get a better job, go back to school or marry some rich person who can

 

 

 

 

 

 

 

 

 

 

 

simples

[un1eash]

I was in higher education long enough so i'll take your other advise and go ask for a pay rise.

[christianmg]

Who cares about MPG anyway? If you do then buy a more economical car

 

I have the aircon on all year round whatever the weather and when it is cold like this I have the heated seat on too I probably burn a small part of the rain forest every trip to work but at least my arse is warm

 

someone told me that having the heated seats on greatly reduces the life of the leather on the seats and cracks the leather?? is this true?

[chrisjones6699]

Who cares about MPG anyway? If you do then buy a more economical car

 

I have the aircon on all year round whatever the weather and when it is cold like this I have the heated seat on too I probably burn a small part of the rain forest every trip to work but at least my arse is warm

 

Ahhhhhhhh Dave, you do realize that I went to the Amazon for Sky one this year to highlight global warming!?

 

I also drive with aircon on constantly and my heated seat! It helps with my bad back!

[Fee]

I must be the only person who when placed next to an obnoxiously revving neighbour at traffic lights, who is trying to jump a queue of cars by going straight from a lane designed for right turns only, apart from all the other obvious necessary steps turns off the aircon, radio & heated seats in preparation...

 

 

Ermmmm I do too...especially if they are male!!!

[sasha@lazytrips]

I must be the only person who when placed next to an obnoxiously revving neighbour at traffic lights, who is trying to jump a queue of cars by going straight from a lane designed for right turns only, apart from all the other obvious necessary steps turns off the aircon, radio & heated seats in preparation...

 

 

Ermmmm I do too...especially if they are male!!!

 

every horse & lb torque counts!