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-   -   Winters : Use Heater with or without compressor? (https://www.team-bhp.com/forum/technical-stuff/131068-winters-use-heater-without-compressor.html)

Mod: Kindly delete/edit/move this thread if repeated (my search didn't yield similar thread).

I was traveling with a relative in his Figo tonight and it is quite chilly outside during the night. He is an enthusiast and loves his cars. He has multiple cars from Figo to X5 and an experienced driver, though he is mostly driven around. He cranked the car and immediately put on the AC. Turned the dial towards heating and blower to face and feet.

I have never done that, I never put on the AC. Though I do not use the heating too much but even in Germany and Scandinavia I had never used the AC knob and still got good heating.

I was so surprised that it came out as "Woah, wait you are doing it wrong". He is senior and didn't take it too well and said without putting the AC ON how will we get the heating and that without it in use, you are only dependent on the engine heating. I remarked that there are heating coils and not the compressor that is used for heating. H then said he has been doing so for years and also on his latest X5. His company driver does it on A4 and its the same story with his personal drivers, his Sons and everyone in his network. I was quite surprised and showed him how the cold engine without the AC On was heating the cabin and how misting is avoided with circulation and windshield and defogger.

I just now spoke to my mother and she said most drivers to this and have to be checked on this. She added that in older gen cars it was actually part of the engine getting warm. My wife too said it was common practice. I just can't digest that many think of the heating being done by AC.

Am I the only one thinking the wrong way or here maybe I was caught between some bozo explosion and not knowing the car well.

Electric vehicles have resistance heaters. But for most ordinary petrol/diesel vehicles, the heating is NOT done by the air conditioning compressor, it is done by the hot engine coolant flowing through the heater core.

I'm sure the compressor probably switches off at the hot end, but if it does not, it'll give you worse heating, since practically every car switches the radiator fan on with the compressor.

You are absolutely right.No need of switching on the AC while the heater is on. This practice is done only when you need to rapidly defog the front windshield.

Infact my i20 has a defog button for the front windshield. On clicking it the ACC switches on the heater,the AC with full fan speed and directs the air to the windshield.The windshield is cleared in a matter of seconds and you can switch it off.

Would he ever switch on an AC and an heater in the same room at home? Its exactly the same thing.

Keep the compressor running along with the heater, to prevent the inside surfaces of your windscreens and windows misting up. All ACC systems run the compressor simultaneously with the heater.

When I turn on AC with heater I feel that I am getting good quality heated air. And without AC I get hot air in which I feel uncomfortable. I do find my observation strange which is without technical explanation.

One reason could be, generally heating coil is located after cooling coil. If we keep A/C on then air is cooled first and then heated back again in heater coil.
Effect of this is that, cooling of air removes moisture from air and heating again moisture free air. Which helps in preventing misting and air feels good as it is free of water/moisture.

Not sure what is right, but what i have observed is this.

• If i turn the dial to heating without switching the AC on the heating takes some time (Until the engine it hot) and once the engine is hot it works well.
• For mild winter (upto 5-7oC) the heating provided (Without switching AC on) is sufficient.
• Have a feeling (No data) that this also results is slightly better fuel efficiency as compared to switching AC on.
• Switching AC on while setting the thermostat to heat gives out warm/hot air instantly, the engine pull drops a bit (As AC is switched on) and i am guessing that this also results in lower fuel efficiency.
• For heavy winters (Closer to 0 or sub 0 temperatures), one surely has to switch AC on (set to heating).
• While in the mountains, if its not too cold its better to use engine heating as AC does not drain engine power.

The time when both are required is misting of the glasses. You need to remove the moisture in the air without cooling the glass so much as to get frosting outside. I may add once frosting starts outside it takes ages to get rid of it.

Easier to manage the outside misting/frosting by liberal use of wipers, than the misting that happens inside.

Whats wrong with that?

AC is an acronym for Air Conditioner and NOT Air Cooler. It is a generic term which could mean both.

From the internet:

Let me rephrase it, why would any one purposely turn on a device that cools air and the one that heats it at the same time?
Also leading to lesser fuel economy.

Leave the defogging apart.

I do agree on the feel good thing posted by other bhpians.

In winters you need to put AC on as putting on only the heater will fog up your windows.
Try this experiment.
Put blower to windsheild and put on blower without AC. Window will fog up.
When you switch on AC, the window will clear

In Winters certainly no need to use the AC along with the heater. In case of mist just switch off the Re-circulation mode and allow some fresh air to come in, automatically with few mins the mist will clear off.

Its not wise to put immediately put AC on as soon as you start the cold engine. This will though, help to warm the engine quickly but in the long run will have a negative impact on the engine, especially the Diesel Engines.

Regards

Amit

Not when the car is standing still or being driven slowly.

Nothing of the sort happens. You can breathe easy, your engine will continue to remain in perfect running condition.

Hi Buddy,

My concern is in extremely cold weather like we have in Delhi, its not wise to immediately put extra load of AC especially when we start in the morning.

In my Sx4, i truly miss the front windshield de-fogger.

BR

Amit

I use only fresh air mode, with the temperature knob is set to hot air, and don't switch on the ac switch. This prevents the stuffiness which occurs when heater is used, ensures inner misting doesn't happen. It is not as warm as it can get when re-circulation mode is used, but this is something which I learn't in leh - one should never try to change the artificial temp to be at a huge variance with actual temperature. That is the easiest way to fall sick - as the body is just not equipped to jump such extremities in temperature.