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Old 19th February 2008, 08:47   #1
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Question Queries wrt auto climate control

Gurus,
I have these queries wrt auto climate control in my SX4, looking for your response!
  1. I normally set the temperature between 24-26 deg C (re-circ mode). There is a significant difference in temp if outside temp is <20 deg Vs >25 deg (I feel hot/normal Vs cold). If the setting is supposed to maintain expected temp, why do I feel the temp difference depending on external temp? Doesn't auto climate control work as expected?
  2. When the vehicle is stopped and when I keep AC on, I notice that the temp inside is hot compared to same settings while vehicle is moving. How does AC outcome is related to vehicle movement?
Sorry if these are very basic questions.
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Old 19th February 2008, 08:51   #2
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1. Takes that much longer for the cabin to cool when your car is burning hot, it may never reach the temp you have set.

2. I guess that is because the AC works best when the alternator gives more juice to the electricals.
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Old 19th February 2008, 09:08   #3
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2 cents
1. The automatic climate control acts on sensing the temperature of the car ( through sensors placed inside the cabin) vis a vis the set temperature. So depending on the sensitivity of the temperature sensor and obviously the prevailing temperature, the climate control CPU would try to increase/decrease the temperature. So if you compare the temperature of inside car to outside air, there should be a difference.

2. Umm, ideally, the battery should be able to power the ac compressor for the time till it is drained but not so sure why a moving vehicle would give more current unless the alternator is directly linked to the compressor. Not sure on this.
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Old 20th February 2008, 20:53   #4
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Quote:
Originally Posted by sathya_nars View Post
Gurus,
I have these queries wrt auto climate control in my SX4, looking for your response!
  1. I normally set the temperature between 24-26 deg C (re-circ mode). There is a significant difference in temp if outside temp is <20 deg Vs >25 deg (I feel hot/normal Vs cold). If the setting is supposed to maintain expected temp, why do I feel the temp difference depending on external temp? Doesn't auto climate control work as expected?
  2. When the vehicle is stopped and when I keep AC on, I notice that the temp inside is hot compared to same settings while vehicle is moving. How does AC outcome is related to vehicle movement?
Sorry if these are very basic questions.
sathya,

Working with automatic temperature control, please understand that a set temperature of 22-23 degC is ideal comfort temperature. In humid conditions like India (although HVAC does dehumidify), 24-26 degC is on the higher side. Just change these settings and tell me how you felt.

Does your instrument cluster show the actual ambient temperature? Can you tell me whether this temperature tends to increase as you slow down the car?
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Old 20th February 2008, 20:55   #5
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sathya,

Working with automatic temperature control, please understand that a set temperature of 22-23 degC is ideal comfort temperature. In humid conditions like India (although HVAC does dehumidify), 24-26 degC is on the higher side. Just change these settings and tell me how you felt.

Does your instrument cluster show the actual ambient temperature? Can you tell me whether this temperature tends to increase as you slow down the car?
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Old 20th February 2008, 21:42   #6
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Short answer is AC compromised for better FE.

Long answer:

Quote:
Originally Posted by sathya_nars View Post
Gurus,
I normally set the temperature between 24-26 deg C (re-circ mode). There is a significant difference in temp if outside temp is <20 deg Vs >25 deg (I feel hot/normal Vs cold). If the setting is supposed to maintain expected temp, why do I feel the temp difference depending on external temp? Doesn't auto climate control work as expected?
If you consider the physics, to maintain the cabin at say 20 deg C when it is freaking hot outside and the car is not very well insulated thermally, your FE might go down drastically and you will see bad reviews about it and the car wont sell.

So manufactures give a digital display, to differentiate it from the cars that don't have climate control :-) Yeah, there is a lame 2-bit climate control super computer which is supposed to talk to GPS and weather forecast systems and control the inlet air temperature, but I don't know if any car actually maintains the inside temperature at the set temperature.

Quote:
When the vehicle is stopped and when I keep AC on, I notice that the temp inside is hot compared to same settings while vehicle is moving. How does AC outcome is related to vehicle movement?Sorry if these are very basic questions.
You might also notice that the 'idle' RPM of the engine will blip slightly up when you put the AC on. I have seen this happen in few cars. I guess the power output at idle speed is not sufficient enough to run the AC optimally.
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Old 20th February 2008, 22:07   #7
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moving vehicle= external radiator will be cooled better, this is inspite the fact that there is an electric fan. also compressor rpm is higher and more efficient.

in a cinema so more details later or wifee might injure me
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Old 21st February 2008, 08:56   #8
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Quote:
Originally Posted by androdev View Post
Short answer is AC compromised for better FE.

So manufactures give a digital display, to differentiate it from the cars that don't have climate control :-) Yeah, there is a lame 2-bit climate control super computer which is supposed to talk to GPS and weather forecast systems and control the inlet air temperature, but I don't know if any car actually maintains the inside temperature at the set temperature.
I wonder where you learnt that Climate control talking to GPS for weather learning. Based on my experience, it isn't such a rocket science.

Quote:
Originally Posted by androdev View Post
You might also notice that the 'idle' RPM of the engine will blip slightly up when you put the AC on. I have seen this happen in few cars. I guess the power output at idle speed is not sufficient enough to run the AC optimally.
This is a compensation for the compressor load torque done on the engine side. This is necessary to ensure a smooth driveability for the driver (not affected by the additional load).
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Old 21st February 2008, 09:56   #9
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My experience with climate control on Corolla for 1 yr is as follows:
1. Summer, dry weather: can put the temp at 27-28C with outside temp at around 30-35.
2. Monsoons, humid weather: even if outside temp is lower, I have to reduce temp to 25-26C.
This is usually at 8-9AM and after 6PM. Of course, if you move out later in the morning, the temp has to be lower.

I have found that dry weather is better than humid weather in keeping higher AC temp.
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Old 21st February 2008, 11:09   #10
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Quote:
Originally Posted by sathya_nars View Post
  1. I normally set the temperature between 24-26 deg C (re-circ mode). There is a significant difference in temp if outside temp is <20 deg Vs >25 deg (I feel hot/normal Vs cold). If the setting is supposed to maintain expected temp, why do I feel the temp difference depending on external temp? Doesn't auto climate control work as expected?
  2. When the vehicle is stopped and when I keep AC on, I notice that the temp inside is hot compared to same settings while vehicle is moving. How does AC outcome is related to vehicle movement?
Sorry if these are very basic questions.
1) can you elaborate more? did you mean to say when you step out you feel the temp diff more OR while inside you have the feeling of temp diff.

2) See there are loads of factors, like ac comp rpm, radiator fan cooling, chanrging voltage and then the wind flow over the body cooling it.
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Old 21st February 2008, 11:28   #11
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[quote=dvswift;730175]I wonder where you learnt that Climate control talking to GPS for weather learning. Based on my experience, it isn't such a rocket science.

Acura RL does this. But nobody else.

I keep my swift control at 28 degrees (with air blowing directly at you). Driving is mostly morning and evening. At noon times you have to set it low say 27.
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Old 21st February 2008, 12:31   #12
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Quote:
2. Umm, ideally, the battery should be able to power the ac compressor for the time till it is drained but not so sure why a moving vehicle would give more current unless the alternator is directly linked to the compressor. Not sure on this.
I hope you are not serious, Ac running running off a battery ?

This is an interesting thread for anyone who wants insight on Auto ACs
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Old 21st February 2008, 12:47   #13
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Guys, from my engineering days, I can tell you that comfort depends upon 3 factors - temperature, humidity and air flow.

So, in the situations you have described, though the temp.is constant, you feel better in one case and not in the other is due to difference n humidity. For eg. in delhi, 35 degree C (less humidity) would feel much more comfortable in Mumbai at 30 degree (humidity close to 100%).

The auto climate can control temp. and air flow but not humidity. Obviously it dehumidifies. (When I say cannot control, I mean both increase or decrease as appropriate). After prolonged use in recirculation mode, air would become really dry.

So, install a humidity guage as well, OR adjust the temp. suit your comfirt level, and if you are going on a really long drive, to increase humidy level, allow some fresh air inside.
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Old 21st February 2008, 14:53   #14
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Quote:
Originally Posted by Technocrat View Post
I hope you are not serious, Ac running running off a battery ?
AC running on battery - quite possible
AC running on car battery - needs some work but possible as long as AC has peak current requirement under maximum current supplied by battery but it won't work for much long. So it basically won't be practical.
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Old 21st February 2008, 15:42   #15
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LOL adya, I knew that, what I meant was that companies dont wire it this way i.e. compressor will run only when engine is running, at least in the current generation cars. Correct me if I am wrong.
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