Air conditioning in auto mode.

Bodywork & Interior problems
Huntsman
Posts: 49
Joined: Wed Mar 21, 2018 5:46 pm
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by Huntsman »

I have always left my air conditioning in auto mode (6 years with Peugeot 3008 and 3 months with QQ J11. I have always believed that the air conditioning will only come on if the car electronics deem it is necessary. However, one of my friends tells me that the air conditioning is on constantly therefore using more fuel.

Is there a straight forward answer to this or does it rely on other factors.

Thanks

Alan
QQ/J11B - 2020 1.3 Dig-T 160 DCT N-Connecta , Ink Blue. 19" alloys
Prev. QQ/J11 - 2015 1.2 Dig-T Tekna, Storm White. 19" alloys.

Deleted User 3871

Post by Deleted User 3871 »

Auto mode can have the aircon on or off.

When the aircon is selected on, then the pump will run. The pump will only run to cool the evaporator to a certain temperature then disengage. so on hot days when u select cold the pump will operate a lot more and use a lot more fuel than on a cold day.
un1eash
Posts: 10
Joined: Sat Jan 20, 2018 7:14 pm
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by un1eash »

Modern cars are a lot better at managing the air con pump, you may see a couple less mpg in summer as its being used more.
Having it switched in doesn't mean its actually on and effecting engine performance. Would need to test it but in my old GT86 when you were accelerating the air con pump would disengage to reduce engine drag.
Ink Blue J11B Tekna 1.2 Dig-T with Glass Roof
Deleted User 3871

Post by Deleted User 3871 »

I had a Nissan Primera GT, and this was one of its selling points when your foot was to the floor it would disengage the aircon. I suspect this is standard on all cars now.
un1eash wrote: Mon Apr 23, 2018 6:49 pm Modern cars are a lot better at managing the air con pump, you may see a couple less mpg in summer as its being used more.
Having it switched in doesn't mean its actually on and effecting engine performance. Would need to test it but in my old GT86 when you were accelerating the air con pump would disengage to reduce engine drag.
Huntsman
Posts: 49
Joined: Wed Mar 21, 2018 5:46 pm
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by Huntsman »

Thanks for the replies guys. I am going to stop worrying and just leave everything on auto.

It works for me.

Alan
QQ/J11B - 2020 1.3 Dig-T 160 DCT N-Connecta , Ink Blue. 19" alloys
Prev. QQ/J11 - 2015 1.2 Dig-T Tekna, Storm White. 19" alloys.
Deleted User 1571

Post by Deleted User 1571 »

Huntsman wrote: Wed Apr 25, 2018 4:53 pm Thanks for the replies guys. I am going to stop worrying and just leave everything on auto.

It works for me.

Alan
For long term reliability its important to actually have it cutting in regularly. Apart from punctures in the system, the biggest cause of air-con failure is lack of regular use. Believe me, the repairs will cost more than any slight extra fuel used over time.
chrisw99
Posts: 541
Joined: Mon Jul 11, 2016 10:42 am

Post by chrisw99 »

See some of the other threads, air con systems dry out if not used regularly, and in modern cars it's best to just leave on all the time. It's not just for cooling, it cleans and dehumidifies the air and is just as useful throughout winter.

When you are at idle, having the AC on causes the engine to run at 50-100 RPM more, but when you are driving about at speed it's driven from the engine, so the only time it would really use a lot more fuel is if you are sat in idling traffic a lot.
Oct 2014 N-tec+, 1.2 dig-T
Deleted User 3871

Post by Deleted User 3871 »

Sorry bud, but this is total bull.

If its a warm day and the AC is working you can expect about 5mpg drop. AC is not a by product like heating, the engine has to work and in this game you don't get anything for free.

Colder days = less work for the ac pump and better fuel consumption.

AC on and idling on a hot day is a lot of stress for the components under your bonnet / hood as the temperatures get a lot higher. Throw in a DPF regen at the same time and its toasty.
chrisw99 wrote: Thu Apr 26, 2018 8:44 am When you are at idle, having the AC on causes the engine to run at 50-100 RPM more, but when you are driving about at speed it's driven from the engine, so the only time it would really use a lot more fuel is if you are sat in idling traffic a lot.
Deleted User 1571

Post by Deleted User 1571 »

Aircon takes about 5hp when the compressor is engaged, which is about a third of the time, even in hot weather once the cabin is down to a reasonable set temperature, say 19C.
That is not going to reduce mpg by 5mpg. Not unless the car only has a tiny engine and the power consumed makes up a high proportion of maximum engine power, like in a tiny Smart car where the consumption might well drop from 55mpg to 50.
In my rather powerful cars, the increased fuel use is neglible and around 1mpg at worse.
Deleted User 3871

Post by Deleted User 3871 »

As with many things I think we are taking general and not specific here. I have read that AC can be 5 - 10 % extra fuel consumption, the ambient weather will make a lot of difference in the duty cycle of the pump, the fuel type, the condition of the components, how many occupants are in the car etc. etc. etc at the end of the day AC is not free and its going to cost you in the pocket by a varying amount no matter what car you drive!
Quacker wrote: Fri Apr 27, 2018 8:28 am Aircon takes about 5hp when the compressor is engaged, which is about a third of the time, even in hot weather once the cabin is down to a reasonable set temperature, say 19C.
That is not going to reduce mpg by 5mpg. Not unless the car only has a tiny engine and the power consumed makes up a high proportion of maximum engine power, like in a tiny Smart car where the consumption might well drop from 55mpg to 50.
In my rather powerful cars, the increased fuel use is neglible and around 1mpg at worse.
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