[sgiitk]

There are two parts to this:

1. Obviously at a higher speed the blower will draw more power. Say 3A, i.e. 36W (or 1/20hp) which is negligible.
2. As the blower runs slower the cooling will be reduced. I suspect the loss here will be negligible, since very seldom do we let the car get so cold as to have the compressor switched off. When running the compressor draws it full power (up to 3-5hp at speed). This is the place where the real juice is consumed! Modern cars do not have thermostats and only switch the compressor off whent he pressure in the system goes low.

[S.H.Shankar]

I believe that the blower unit does consume some power, sufficient to affect FE ever so slightly. I have noticed in more than one vehicle (including my own Innova) that switching the blower on at full in an idling vehicle momentarily dips the idling r.p.m. This means that the blower at full power does add sufficient load to the engine (through the alternator) so as to make it felt.

As far as cooling is concerned, I for one always prefer my blower set to tornado mode. I feel much more comfortable that way.

[gpa]

Originally Posted by S.H.Shankar

I have noticed in more than one vehicle (including my own Innova) that switching the blower on at full in an idling vehicle momentarily dips the idling r.p.m. This means that the blower at full power does add sufficient load to the engine (through the alternator) so as to make it felt.

As far as cooling is concerned, I for one always prefer my blower set to tornado mode. I feel much more comfortable that way.

I have noticed the same in my Alto. On speeds 1-3 the blower seems fine, increase it to the max of 4 and you feel a slight change in the engine RPM. I rarely use speed 4 in my car, but have noticed the change.

[Shashwat B]

Looks like my post is coming in 10 long years laters.
For the benefit of other users/members I shall share my little experiment.

Car - Hyundai Elantra 2005 ( Petrol)
Month of April and May 2019
Location- Bangalore

1. After filling the tank. I used the car with AC set at 17°C with outside temperature around 30- 32° C. Blower speed was kept at the highest.

Observations - The performance was hit hard. The engine would grunt during heavy acceleration. Rpm needle would rise but the speed would increase in a lethargic manner. As the driving was done in city only, this was during overtaking at speeds of 30 to 70kmph.

Fuel efficiency- 8kmpl ( it was 8.13, I am rounding it to 8)

2. Another tank full, but now, I kept the blower at speed 2 and rarely 3. No noticeable change in performance. It continued to perform as in above case.

Fuel efficiency - 8.4. Kmpl but this could be due to an airport trip. ( 60kms to and fro).

3. Now, Temperature was set at 24° C. Blower speed was at low and about 20% of the time, at Max.

Performance- car performance was a notch below driving without AC. Although the lithargic attitude would be present at crawling speeds. But once at 30kmph. Performance was good.

Fuel efficiency- 10kmpl ( around 10.24 rounded off)

Method used- Tank full to tank empty method.
Person driving the car - Me. No change in driving style.

Conclusion - I hope this brings value to these series of posts.
This experiment may yield different results based on your car, age of car, fuel type, condition of AC Gas etc.

Note - The AC compressor gas has not been refilled in over 2 years. AC does a good job. During this experiment I tried to keep the driving conditions as similar as possible.

Thanks for reading

[Aroy]

Yes that is normal for car with AC on. The lower the set temperature, the more power it sucks from the engine. Similarly the smaller the engine the more hit on FE. In some larger engined cars you may find no FE hit with AC on at reasonable speeds.

[KaurDiCar]

Me and my husband make a journey from Gurgaon to Greater Noida almost 3 times a week, Sometimes in his Spresso and sometimes in my Thar. While my Thar has been fairly consistent with FE figures given that we come and go in peak hours, my husband's Spresso is a different story.

While we go in the morning when it's far warmer and the AC runs on 3, we are getting a mileage of 10 kmpl as per the MID, and by the evening when it's cooler and the AC runs on 1, we get around 13kmpl.

The difference isn't small considering a similar amount of traffic and the same driving style.

Would love for the forum to shed some light on this.

[Turbanator]

Originally Posted by KaurDiCar

when it's far warmer and the AC runs on 3, we are getting a mileage of 10 kmpl as per the MID, and by the evening when it's cooler and the AC runs on 1, we get around 13kmpl.
The difference isn't small considering a similar amount of traffic and the same driving style.

Can be attributed to the time Compressor in the car was working. If the fan speed is less, compressor usually trips faster, at least on regular A/c systems. Plus, perhaps, subconsciously, we are driving faster in the morning, trying to reach the office on time/ finding space for parking/ catching-up the pending work whereas back home is usually stress-free.