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Old 16th June 2006, 10:30   #16
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[quote=varunroy]
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Are you trying to imply that the compressor and the heater are both working at the same time.

Yes, definitely. It is very useful for demisting.


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I am sorry but a shower mixture works in a different way. There is no thermostat in the mixture that controls the temp ot the water. The Hot and the cold water comes from two different sources and the mixture just blends the 2 to the desired requirement. While In the AC/Heater system the two never ever work together. The inbuilt system switches off either of them depending on the Cabin temp required.
Some cars do not allow the simultaneous operation, but maruti cars for sure allow simultaneous operation (for the same demisting reason)

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While the AC relies on the compressor which is driven by the Engine the Heating element/coil derives its huge power requirements from the battery.
Electrical heating is used is some cars only for instant heating required in countries where the wheather is very cold. It is also used for diesel engines to heat the block (to aid starting), not for cabin heating. Commonly a heater core is used. Hot coolant from the engine is used for heating the air. Once engine is warmed up, this "heater" is always "ON".

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Therefore for you to say that the heater aids in engine cooling would be a wrong statement.
Because of engine coolants heat being absorbed as said above, it acts like a secondary radiator system which definitely helps in cooling the engine.
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Old 16th June 2006, 14:10   #17
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Santosh.. have you ever actually observed the compressor cutting off?
I my Swift VXi, which has manual HVAC, if I switch the AC (compressor) ON, it just doesn't cut off. This is regardless of the temperature knob setting, which itself is just an hot/cold air mixer.

So... my assumptions are:
1. Swift VXi compressor keeps on running as long as the switch is ON. There is NO thermostat to cut it off.
2. Temp control knob on the dash is just a hot/cold air mixer.
3. There is no way to put the heater off. However putting the temp control knob on the coolest position will effectively stop the hot air from entering the cabin.
4. As the compressor is always on (unless manually put off) there is no question of it getting overloaded because of cooling hot air (coming through the heater).
I think even Baleno HVAC must be having similar properties.
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Old 16th June 2006, 15:33   #18
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Guys..

rather pointless discussion..The AC and the Heater DO NOT WORK SIMULTANEOUSLY!!..

Moderators -- ..??
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Old 16th June 2006, 15:44   #19
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Quote:
Originally Posted by k36
So... my assumptions are:
1. Swift VXi compressor keeps on running as long as the switch is ON. There is NO thermostat to cut it off.
I "guess" that should not be the case. May be the thermostat in your car is faulty... check it. Other swift oweners, please comment on this and let us know the fact.


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2. Temp control knob on the dash is just a hot/cold air mixer.
Same is the case with baleno. In fact my concernes are applicable only for such systems... I had started this thread with the assumption that most manual cars have same mechanism.

Quote:
3. There is no way to put the heater off. However putting the temp control knob on the coolest position will effectively stop the hot air from entering the cabin.
As mentioned earlier, I am aware of this. But the intention is to shut off the heater while using the mixer for cool air (from AC) and the circulated air (ambient). I want to find out if it is possible to achieve this without modifications (preferrably) or otherwise even by doing some modification.

Quote:
4. As the compressor is always on (unless manually put off) there is no question of it getting overloaded because of cooling hot air (coming through the heater).
I think even Baleno HVAC must be having similar properties.
If your compressor is always ON, then it is already putting the highest possible load on engine! But as I said earlier, this should not be the normal fuctionality. Baleno surely cuts in and cuts off.
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Old 16th June 2006, 15:44   #20
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Quote:
Quote:
Originally Posted by headers
Guys..
rather pointless discussion..The AC and the Heater DO NOT WORK SIMULTANEOUSLY!!..
Moderators -- ..??
To be more precise, they should not and if they do then there is some problem with the system and needs to be checked.

So long....
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Old 16th June 2006, 15:54   #21
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Quote:
Originally Posted by headers
Guys..

rather pointless discussion..The AC and the Heater DO NOT WORK SIMULTANEOUSLY!!..

Moderators -- ..??
I can bet that it DOES work simultaneously. It is clearly mentioned in the baleno manual itself. Ask any baleno owner or see the manual yourself. What other proof do you need ? ( I can provide others as well)

It may be pointless for you... in that case you are free to keep away from the thread. But, at least, let other people take the discussion further, who may have gotten the point... shouldn't you??
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Old 16th June 2006, 15:58   #22
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Quote:
Originally Posted by varunroy
To be more precise, they should not and if they do then there is some problem with the system and needs to be checked.

So long....
I am surprised! I have already addressed this point a couple of times. It is NOT AT ALL WRONG to have both compressor and heater ON at the same because it is really useful for demisting windshields and window glasses. But it IS WRONG if it is used for normal cooling operation.

Thats EXACTLY my point, we should be able to switch OFF the heater when we are using it for usual cabin cooling, and put it ON for demisting/dehumidifying/defrosting operations. In both cases we should be able to effectively utilize the temperature control (or rather the mixer). But that flexibility is not provided by manufacturers, so I am looking for some modifications!

Last edited by santosh.s : 16th June 2006 at 16:18.
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Old 16th June 2006, 16:31   #23
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Quote:
Originally Posted by varunroy
Are you trying to imply that the compressor and the heater are both working at the same time.
Actually, YES: The car's engine is a heater for the duration it is running! The AC compressor is the "extra" load... it is mechanically coupled to the engine via. an electrical clutch mechanism. The compressor has an outer wheel that is spun by the engine's fan / waterpump / alternator belt. When you engage the "AC" switch, power is fed to the electrical clutch on the compressor, it "locks" the inner wheel of the compressor with the outer wheel so that the compressor starts ... erm, compressing!


Quote:
Originally Posted by varunroy
While the AC relies on the compressor which is driven by the Engine the Heating element/coil derives its huge power requirements from the battery.
I think that you are confusing the "heater coil" with "glow plugs" found on deisel engines. In *most* cars (deisels included), the "heating coil" is actually a coiled tube (similar to the condensor coil) through which some of the engine coolant is redirected. It only heats when the coolant is hot and has nothing electrical to do with it. Whether this transfer of heat would significantly cool the engine is debateable.

Coming to the real topic: Car either gets too hot or too cold -

"Climate control" systems have *true* thermostat controlled temprature settings. In conventional HVAC systems, the thermostat is preset to chill the air to around 4 degrees C. It is more of a safety system than a temp control: The amount of "cooling" in the evaporator coil (the coil under the dash that gets cold) depends on the pressure of the compressed gas. This pressure depends on the rpm of the compressor which in turn depends on (you guessed it right!) the engine rpm.

Unlike your home AC, the compressor does not spin at a constant speed in your car. At high rpms, the evaporator coil can get too cold and freeze up (gas inside will reach such a high pressure that it will stop evaporating). This can lead to the pipes bursting etc. The "fixed" thermostat is actually in place to avoid such situations... when temp drops below 4 degrees, compressor is cut off.

To really control the temp in the cabin, you would need to *manualy* mix hot / cold air. I'm not sure, but I think that climate control systems do this as well, albeit automatically. Why all this mixing you ask?

Well: Cost & Complexity. It is too complex to compute whether the compressor should be off / on based on exact cabin temp (note that it is not even uniform !), engine rpm etc. If you dont mind paying extra (and it is an option in your car) then go for "Automatic Climate Control" ... otherwise live with "Manual Climate Control" aka "Sliding the mixer knob and / or switch on / off the compressor"

Just my 10paise ...

- T u r b o C -
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Old 16th June 2006, 18:54   #24
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Hey turbo_c, thanks a lot! That was pretty informative, not only for me but should be for others as well That exactly matches with my beliefs about car HVAC operation, but I was not 100% sure about everything. The discussion so far sounded as if I had some weired, non-sense idea in mind to talk about... you proved it wrong Anyways, I knew what I was saying, though.

Coming back to the real topic:

Yes, engine RPM is another (rather important!) factor in car HVAC systems. I had an idea as to how difficult it would be to account for that... that obviously means "Auto climate control"... actually I am doubtful, even that may not account for RPM (because otherwise I would expect them to include that point in advertisements for sure) As a ground reality, my choice has already been made- its manual!

Now, I am not trying to convert this manual system into automatic either, simply because of the complexity which do not seem to be practical at all, as you have already explained. What I wanted is this- just by having a "little" modification either to heater core's coolant inlet/outlet plumbing or its air inlet/outlet plumbing, we can considerably improve the operation of temperature control knob while using it for cooling operation. Note that for heating, it is already the way I want it to be (i.e. we can switch off the other part- AC)... but for cooling it is not so and thats why we need some modification to make it work that way! At the same time I don't want to sacrifice the ability to use both AC/heater simultaneously. Minimizing temperature deviations is the main reason, fuel savings (if any) will be a bonus.

The intention of this thread was to explore whether or not such a modification-

- is already common place
- is tried out by anybody on the forum
- would be worth doing it
- would be practically feasible
- would be cheap
- would poses any serious risks
(I guess none if quality of work is good, except for warranty issues)
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Old 16th June 2006, 19:47   #25
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Quote:
Originally Posted by turbo_c
In conventional HVAC systems, the thermostat is preset to chill the air to around 4 degrees C. It is more of a safety system than a temp control: The amount of "cooling" in the evaporator coil (the coil under the dash that gets cold) depends on the pressure of the compressed gas. This pressure depends on the rpm of the compressor which in turn depends on (you guessed it right!) the engine rpm.

Unlike your home AC, the compressor does not spin at a constant speed in your car. At high rpms, the evaporator coil can get too cold and freeze up (gas inside will reach such a high pressure that it will stop evaporating). This can lead to the pipes bursting etc. The "fixed" thermostat is actually in place to avoid such situations... when temp drops below 4 degrees, compressor is cut off.
@k36, this is the reason why I had suggested you to check the thermostat in your car.
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Old 23rd June 2006, 18:46   #26
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Quote:
Originally Posted by turbo_c

Well: Cost & Complexity. It is too complex to compute whether the compressor should be off / on based on exact cabin temp (note that it is not even uniform !), engine rpm etc. If you dont mind paying extra (and it is an option in your car) then go for "Automatic Climate Control" ... otherwise live with "Manual Climate Control" aka "Sliding the mixer knob and / or switch on / off the compressor"

- T u r b o C -
Turboc, you are right. But I seriously feel that at least adding another "air flow" control to bypass the heater core would be neither too complex nor costly. What do you say? That extra switch could have been called "heater" - on/off!

I had a glance at baleno's engine compartment, I could figure out a relatively thin pipe branching out of main coolant pipe from the engine. The big pipe connects to the radiator (obviously) and the thin pipe enters the middle portion of dash. I am sure (well, almost!) that it is leading to the heater core. There is similar "return" connection as well. Since all operations on air (heating, cooling, mixing, flow control) happen inside the dashboard, could not see any further

I need to take help from a befriended, experienced/skilled mechanic (or team-bhpian for that matter!) to explore further... safely! I don't know of any such person for time being, so if anybody is interested to help me out, then I would really appreciate them very much...

I am sure it would be much much safer to play around with air flow rather than the coolant anytime. "may be" we can make use of valves that are already being used to control various air flow modes?? Since these controls are electic, it can probably make life easier, shouldn't it?
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Old 24th June 2006, 18:53   #27
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well santhosh,

i doubt the heater is on all the time..can you clarify that?
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Old 24th June 2006, 22:44   #28
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Quote:
Quote:
Originally Posted by headers
well santhosh,

i doubt the heater is on all the time..can you clarify that?
Hang on for some time. Even I share your thoughts but we could be wrong. I am sourcing the Service manual of a Baleno from MASS, shall study/discuss the subject and post observations. On hind sight I think I have'nt really understood the problem.

So long....
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Old 25th June 2006, 09:38   #29
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Hi Varun, thats great...service manual will help a lot!
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Old 25th June 2006, 12:48   #30
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Quote:
Originally Posted by headers
well santhosh,

i doubt the heater is on all the time..can you clarify that?
Check this out

http://auto.howstuffworks.com/cooling-system10.htm
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