[McLaren Rulez]

Related question here: Sometimes, the outside temperature is perfect and there is no need for AC. However, when driving on the highway, I'd like to keep the windows shut to reduce wind noise.

I find that leaving the blower on (speed 2) and AC off in fresh air mode doesn't ventilate the car sufficiently. It gets stuffy after a while with three adults inside. Is this the case in most cars?

[arunphilip]

Originally Posted by McLaren Rulez

Sometimes, the outside temperature is perfect and there is no need for AC. However, when driving on the highway, I'd like to keep the windows shut to reduce wind noise.

I find that leaving the blower on (speed 2) and AC off in fresh air mode doesn't ventilate the car sufficiently. It gets stuffy after a while with three adults inside. Is this the case in most cars?

Nice question!

The thing is, when you say the temperature outside is perfect, that is the ambient temperature in an open space.

However, the fresh air mode takes air from the vents at the bottom of the dashboard (see picture below) and feeds that in through the firewall into the car. Now, the air temperature in such a situation will be affected by localized temperature also - namely the heat soak that occurs in the engine compartment. With the motion of the car, that heat is moving closer to the firewall, and in turn raises the temperature of the inlet air just enough to take the comfort out of it.

The second thing is, in a closed car, the perspiration of the occupants raises the humidity of the air. More than heat, it is humidity that causes discomfort since higher humidity prevents sweat from drying off and thereby cooling you. When the AC is running, it also dehumidifies the air, improving comfort levels. When the AC is off, this humidity has nowhere to go (it cannot just be ejected from the passenger compartment).

So, the gist of it is - keep the AC running - even if the temperature isn't set so you feel cooler, it will still dehumidify the air and improve comfort.

[McLaren Rulez]

Originally Posted by arunphilip

The second thing is, in a closed car, the perspiration of the occupants raises the humidity of the air. More than heat, it is humidity that causes discomfort since higher humidity prevents sweat from drying off and thereby cooling you. When the AC is running, it also dehumidifies the air, improving comfort levels. When the AC is off, this humidity has nowhere to go (it cannot just be ejected from the passenger compartment).

Good answer! Now that I think about it, I suspect the second point is the main contributor to the stuffy feeling. Guess the AC has to be on or the windows must be opened unless it is a lot colder outside.

Now that I think about it, those butterfly windows on some MPVs as well as those quarter-glass windows that could opened in older cars make so much sense! They help the air actually flow through and out of the car with minimal noise - precisely what one needs in this situation.

[Sedate driver]

Reviving an old thread..

In my Hector I often make round trips of 220 kms and usually have the AC set to auto. The AC setting will be mostly in 24 - 24.5 deg C. Generally the cooling is very effective in Hector and the blower speed will be in minimum when the set temperature is reached. however I experienced fatigue, eye strain and lips cracking after the drive. I really needed a rest of 3-4 hours after every such drive. In Hector when auto is selected, the AC is always in re-circulation mode and selecting the fresh air mode disables the automatic climate control. So I thought of trying the fresh air mode for the entire drive barring dusty, smelly and smoky stretches during which I switch to auto mode and quickly get back to fresh air mode once I cross such zones. To my surprise there is a big difference with almost nil fatigue, eye strain and cracked lips. So the question here is whether to drive in fresh air mode only in highways is advisable as I doubt the external dust will definitely get into the system thereby clogging the filters and ducts. And why the automatic climate control re-circulation mode causes fatigue? Is it because of the lack of fresh oxygen inside?

[Jeroen]

Originally Posted by Sedate driver

. In Hector when auto is selected, the AC is always in re-circulation mode and selecting the fresh air mode disables the automatic climate control.?

That is very odd. I have never come across an AC system that keeps the AC in permanent recirculation mode.

Most AC system when switched on might go into recirculation mode for a few minutes to drop the inside temperature quickly. But they should go back to normal circulation always.

Recirculation mode is not meant to be used permanently. As you are noticing, it creates an environment lacking sufficient oxygen!

Every single AC system, on a car, a ship, an airplane, requires constant supply of some fresh air for this very reason.

I suggest to check your owners manual what it says, or maybe another Hector owner can shed some light on this.

Jeroen

[Rodie09]

I own a Tata Safari XZA+ and I think I have not completely figured out how the ACC is set to work. Few points where I am looking for direction:

1. The ACC to my understanding is going to keep the temperature at a set point unlike a manual AC car where the cooling power is fixed (based on setting) but final temperature may vary and user may need to adjust cooling or fan according to needs. So, in simple terms ACC is nothing but how the AC works in our homes trying to keep a fixed temperature. Right? All good until this point and the ACC in Safari also works like this.

2. However, like someone pointed out above, if you touch any button - modes, recirc/fresh the AC will come out of Auto. Is this normal, even when I change mode to direct air at my feet? I find it odd and expect the AC to remain in Auto for this. No?

3. I'd agree that touching fan speed will bring it out of Auto and it does. But then in manual mode if I change temperature, it adjusts the fan speed. Isn't that odd? Isn't that what it does in Auto anyway?

Am I missing anything fundamental about ACC operation?

Thanks!

[Jeroen]

Originally Posted by Rodie09

I own a Tata Safari XZA+ and I think I have not completely figured out how the ACC is set to work. Few points where I am looking for direction:

Am I missing anything fundamental about ACC operation?

Most AC systems will go out of auto when you touch any of the control buttons.

All of these questions are very likely addressed in the owner's manual I would think. Did you check?

[mathewspaul]

Originally Posted by Rodie09

2. However, like someone pointed out above, if you touch any button - modes, recirc/fresh the AC will come out of Auto.

This is the same in my Nexon also.

[Sedate driver]

Originally Posted by Rodie09

3. I'd agree that touching fan speed will bring it out of Auto and it does. But then in manual mode if I change temperature, it adjusts the fan speed. Isn't that odd? Isn't that what it does in Auto anyway?

Am I missing anything fundamental about ACC operation?

Thanks!

In manual mode if you adjust either the temperature or fan speed, there shouldn't be a change in the other parameter. Isn't it the basic requirement of manual mode? Did you check after changing the temperature, are you able to vary the fan speed manually and the fan speed doesn't vary after that?

[Jeroen]

Originally Posted by Sedate driver

In manual mode if you adjust either the temperature or fan speed, there shouldn't be a change in the other parameter. Isn't it the basic requirement of manual mode? Did you check after changing the temperature, are you able to vary the fan speed manually and the fan speed doesn't vary after that?

There are a few possibilities. As I mentioned the owner manual is likely to give the answer.

On most cars, If you engage manual mode, nothing gets controlled. So setting the temperature doesn’t do anything. In many system when switching to manual, the temperature digits disappear altogether. All you can do is alter the fan speed, valve positions, add heat and so on.

What I suspect in this case: Manual mode means the temperature gets regulated by only fan speed. In auto mode it will control fan speed, heating and the positioning of the various flaps and valves, including recirculation. It will take into consideration outside temperature, sun soak and so on. The idea being that on auto the cabin temperature is controlled more precisely and more comfortably.

When all is said and done, in terms of temperature control the fan speed is the single largest factor. (Apart from adding heat of course).
When in manual mode, Does it actually regulate the fan speed down as the temperature inside drops?


Jeroen

[NomadSK]

Originally Posted by Sedate driver

So the question here is whether to drive in fresh air mode only in highways is advisable as I doubt the external dust will definitely get into the system thereby clogging the filters and ducts. And why the automatic climate control re-circulation mode causes fatigue? Is it because of the lack of fresh oxygen inside?

I know, some car models automatically switch modes (re-circulation to circulation mode) based on the air moisture/humidity levels inside the cabin.

Why would it do that? And how would it do that? It would require an additional sensor for measuring the air moisture content.

Thats true, there are additional sensors to monitor humidity levels and in some cars also for pollution (PM). Based on that, the AC mode keeps on changing as per the requirement. For short runs, one may not notice this though.

https://www.seat.com/car-terms/h/humidity-sensor

A special sensor system reduces misting-up of the windows and enhances comfort by managing the humidity levels inside your car. From the data delivered by the humidity and temperature sensor in the base of the interior mirror, the climate control unit calculates the dew point temperature of the air - that is, the temperature at which the air humidity would condense and cause misting. An infrared sensor remotely measures the radiated heat on the windscreen, and calculates the window temperature. To prevent the windows from misting up, the automatic air conditioning system regulates the air humidity

This is what the Car's owner manual says;

[Jeroen]

Originally Posted by NomadSK

I know, some car models automatically switch modes (re-circulation to circulation mode) based on the air moisture levels inside the cabin.

This is what the Car's owner manual says;

Why would it do that? And how would it do that? It would require an additional sensor for measuring the air moisture content.

Some/most AC systems will switch to recirculation mode when switching to defrost mode automatically. Because it is the fastest way of extracting moisture from the air. I am not familiar with any car AC system that has an actual moisture sensor.

Jeroen

[Sedate driver]

Originally Posted by Jeroen

I suggest to check your owners manual what it says, or maybe another Hector owner can shed some light on this.

Jeroen

I checked the user manual and there seems to be no mention about the auto mode. But it is suggested not to use the re-circulation mode continuously for long drives.