[bullboy]

This is my understanding How HVAC works on my ikon.
1) Switch on a/c blower and temp knob to cold. Compressor runs with the engine and cools the cabin and it keeps on cooling.
2) Change the temp knob to mild/medium ,the hot air from engine coolant system mixes and regulates the temp .Compressor keeps running.
3) Switch off the a/c knob and keep the temp knob in cold position.Compressor stops.
4) Turn the temp switch to hot with a/c switched off .Hot air blows into the cabin.

Compressor will not switch off unless I switch off the a/c or the blower .I believe this is how it works in budget cars without climate control.

[diesel_power]

After reading all the above discussion, I have come to a simple conclusion (for cars without auto climate control). "If you feel that the car has become very cold inside, simply switch off the AC (read: Compressor). Switch it on when you feel its become warm. Don't, even by mistake, touch the temperature adjustment."

[Rodie09]

Originally Posted by bullboy

This is my understanding How HVAC works on my ikon.
1) Switch on a/c blower and temp knob to cold. Compressor runs with the engine and cools the cabin and it keeps on cooling.
2) Change the temp knob to mild/medium ,the hot air from engine coolant system mixes and regulates the temp .Compressor keeps running.
3) Switch off the a/c knob and keep the temp knob in cold position.Compressor stops.
4) Turn the temp switch to hot with a/c switched off .Hot air blows into the cabin.

Compressor will not switch off unless I switch off the a/c or the blower .I believe this is how it works in budget cars without climate control.

I'd want to completely agree with what bullboy says about his ikon. I have a Santro and an Alto and I have observed that on both these cars, there is no thermostat driven auto cut off/cut on mechanism for ac compressor.
The only way the compressor is switched off or on is by pushing the button manually.
And I doubt if such mechanism ever existed on Zen or any other regular hatch without ACC.
The best way to judge this in a car and as well as home ac is that if the compressor has gone off, you can immedeately feel that air temperature gradually starts going up and also the air becomes a bit humid/smelly and difficult to breathe in some time. This never happens when I keep the car ac on, but I can see the difference right after I switch compressor off. If it had been cutting on and off on its own, I'd have surely felt the difference in air quality as I do in my bedroom split ac which cuts in and cuts off every few mins.
Can someone confirm there is thermostatic cut on cut off on Alto or Santro?

[sagarpadaki]

Originally Posted by Rodie09

I'd want to completely agree with what bullboy says about his ikon. I have a Santro and an Alto and I have observed that on both these cars, there is no thermostat driven auto cut off/cut on mechanism for ac compressor.
The only way the compressor is switched off or on is by pushing the button manually.
And I doubt if such mechanism ever existed on Zen or any other regular hatch without ACC.
The best way to judge this in a car and as well as home ac is that if the compressor has gone off, you can immedeately feel that air temperature gradually starts going up and also the air becomes a bit humid/smelly and difficult to breathe in some time. This never happens when I keep the car ac on, but I can see the difference right after I switch compressor off. If it had been cutting on and off on its own, I'd have surely felt the difference in air quality as I do in my bedroom split ac which cuts in and cuts off every few mins.
Can someone confirm there is thermostatic cut on cut off on Alto or Santro?

We owned a Santro and i could definately feel the Compressor cutting on/off .There was this distinctive "Click" sound that was heard when ever it switched on.And the radiator fan also starts spinning faster.Try checking it by driving in some silent road

[sgiitk]

Thermostats switching the compressor on and off went out of fashion well over two decades ago. The pressure switch on the system did switch off the compressor when you were on the verge of freezing. Modern system rely on feeding some hot water into the AC radiator to maintain the temperature.

With climate control, the outside sensor ensures that the compressor does not come on once the outside temperature is significantly lower that the settings.

[ACM]

Few Layman notings;

Safari 2001 - The AC Knob adds the hot and cold air to match the selected temperature setting. It does cut off the AC when it reached the target temperature. (Announced by a very visible change in RMP and Noise while in idling the vehicle.

Laura 2006 - Dual ACC - (Seperate temp zones for LHS and RHS side.) - The ACC settings are designed for Europe and dont allow the car too cool sufficently unless the Temp is set at 21 degree C or less. Yes the AC compressor is cut off even at temperatures of 25 degrees resulting in hot Air blowing in. For a guy like me who really never wants his car too cool the AC works fine - everyone else who sits in the car curses the AC.

Aria 2010 - Climate Control - ACC setting ensure that the Compressor is cut off when the temerature selected is reached. Since the blower air actually hits the Driver hands a fair bit one is able to clearly observe that for the same temperature of say 26 degrees C the AC blows in cold air when it is the summer and hot air when it is Winter - In short works as it should. People love the AC and except for the fact that the driver side AC vents blow straight on to the hand causing me to close driver side the AC vents the ACC works perfectly as it should.

Yes in older cars the AC did not exactly switch off at times when the inside temperature was reached and Yet there has been a transition over the last decade with some cars having AC compressors that switched off (declutched) even in manual AC.

Am not an AC expert but am sure of the above experiences.

[thoma]

Originally Posted by diesel_power

After reading all the above discussion, I have come to a simple conclusion (for cars without auto climate control). "If you feel that the car has become very cold inside, simply switch off the AC (read: Compressor). Switch it on when you feel its become warm. Don't, even by mistake, touch the temperature adjustment."

Oh no. A temperature sensitive like me would want the temperature to be more or less constant. I like 22/23 the most! Moreover, I would be distracting myself too often switching on and off the A/C, if I do not touch the temperature button. Or else, I am likely to get a cold easily due to wide change in temperature. I have experienced that the frequent distraction is a huge safety concern.

Originally Posted by sagarpadaki

There was this distinctive "Click" sound that was heard when ever it switched on.

This definitely was the case with our Matiz. Adding to it, I have noticed in the Matiz, that if we were to climb an incline and we are flooring the pedal(read as huge load on the engine), the compressor would cut off.

[sgiitk]

Originally Posted by thoma

This definitely was the case with our Matiz. Adding to it, I have noticed in the Matiz, that if we were to climb an incline and we are flooring the pedal(read as huge load on the engine), the compressor would cut off.

Almost all cars have the AC equivalent of a kickdown which cuts the compressor off.

[mempheS.D]

Now that we have a good discussion re-initiated on this topic of Air-Conditioning.... I'd like to ask members on this forum, what according to you would be the best practice to follow in order to get maximum life and performance off a car ac compressor?

Is it ok to simply switch off the car, pull the keys off and walk away from the car without even bothering to shutdown the compressor? That would mean that, while re-starting the car, the battery would need to bear the load of the compressor too, correct? And that according to me, can be cause for trouble ??

And if all this does not apply, please let me know.

I was googling for tips, and all I found was this statement, "The Best way to kill you car ac compressor is not using it! Irrespective of weather conditions, it's best to run your compressor as much as possible and comfortable."

[ACM]

Originally Posted by mempheS.D

Now that we have a good discussion re-initiated on this topic of Air-Conditioning.... I'd like to ask members on this forum, what according to you would be the best practice to follow in order to get maximum life and performance off a car ac compressor?

Is it ok to simply switch off the car, pull the keys off and walk away from the car without even bothering to shutdown the compressor? That would mean that, while re-starting the car, the battery would need to bear the load of the compressor too, correct? And that according to me, can be cause for trouble ??

And if all this does not apply, please let me know.

I was googling for tips, and all I found was this statement, "The Best way to kill you car ac compressor is not using it! Irrespective of weather conditions, it's best to run your compressor as much as possible and comfortable."

The answer would depend on the type of AC that a car has.

1) Modern ACC - Climate Controlled AC. - Perfectly ok to walk away without touching the switches. The ACC in conjunction with the ECU is designed to start the compressor only after the car has started and infact if the battery is at low power even the ACC blower will be switched off to enable the engine to start with the available battery power. Also not fiddling too much with the ACC switches will ensure high life of those components. Lastly the ACC will remember the last setting when you switched off the car and revert back to that when you start. It will initially keep the blower high to enable the AC air to cool down the car and then gradually on it's own reduce the AC air levels. Besides in modes like defogging etc it on it's own figures our temp levels, blower levels and which vents to keep on and which to keep off.

2) Modern AC but not ACC - Here too in some cases it is ok to switch off the AC and not so in some depending upon the car. The thing is modern car ECU's will ensure that the compressor load will kick in only once the car engine is started and slightly heated. - But this varies from car to car and needs to be observed for the specific car from the point of view of checking when the compressor starts. (One can hear the sound, instant cold air as well as see the engine revs buildup a notch)

3) Earlier car AC's - Do not switch off the car just like that- It is best to move the blower to zero rather than fiddling with the AC button as that automatically also cuts off the AC compressor plus ensure that at start up the AC blower too will not start up leaving full power for the Battery to start the car.

[mempheS.D]

Thanks ACM ! I ll need to check which category my Skoda Fabia Elegance 2011 falls under. I think it would be category 3. As I've observed that the compressor does turn on immediately after I crank up the engine. Although, I hope it would have categorized under 2. Maybe the next car... I'll mind this. Please let me know if you have a definitive idea on what compressor the Fabia runs.

[ACM]

Originally Posted by mempheS.D

Thanks ACM ! I ll need to check which category my Skoda Fabia Elegance 2011 falls under. I think it would be category 3. As I've observed that the compressor does turn on immediately after I crank up the engine. Although, I hope it would have categorized under 2. Maybe the next car... I'll mind this. Please let me know if you have a definitive idea on what compressor the Fabia runs.

Nope do not have an definitive Idea on the AC system in the current Fabia. But somehow feel in todays times it must be of the type 2 mentioned by me earlier. When you switch on the car do you almost immediately get cold air blowing immediately or is it a bit later. Yes air would blow from the Air vents but that could be with the compressor off and the compressor may cut in a bit later.

[jessie007]

Great thread! This question just came to my mind and found the answer on Team BHP only on googling. I knew that the window and split A/C turn-off the compressor when the set temperature is reached, but was wondering how the temperature knob in the car, instantly varied the temperature of the air being blown through the blowers. I also knew that the heater in the car works by passing air through the warmed up radiator, as in winters, it took time till the car warmed-up and one was able to feel warm/hot air being blown through the vents inside the car.

I indeed used to lull myself into thinking that by keeping the temperature control knob at less than coolest position, I will be using less fuel and the compressor might be using less power from the engine. Though the main criteria is to avoid a drastic difference between the outside and inside temperature, so as to be able to acclimatise easily when one gets out of the car. Also, it doesn't seem practical to keep switching the A/C compressor on/off frequently in a car with manual A/C.

One thing is not absolutely clear to me - what is the affect of fan speed on the compressor (power drawn from engine) and the fuel consumption?

[saket77]

I would like to ask that does the blower speed matter when it comes to the extra load put on the engine by turning on the a/c or even fuel consumption?

For example, will it matter if I am using the A/C with blower on the first speed setting? And will shifting to setting 3 (or whatever is highest speed of the blowr in that particular car) will change the compressor behaviour/ engine load/ or affect FE of the car?

I would be interested in the answers in the the perspective of both newer and older cars, if they are different.

Also, my presumption is that when using only the blower or even the heater (without switching on the compressor) does not affects the FE & performance of the car, unlike A/Cs. Please share your knowledge on this too.

Thanks & regards,
Saket

[EFF-EIGHT-BEE]

Originally Posted by saket77

I would like to ask that does the blower speed matter when it comes to the extra load put on the engine by turning on the a/c or even fuel consumption?

Load on engine yes! The electric load on the alternator increase with increase in speed but its cumulative effect on actual FE will be very very less, much less so as to reflect on the FE figures calculated. So the blower puts load? Yes, but slowing it down to get more efficiency is not that great idea, so use it as much as you want and enjoy cooling.