Sunday, January 21, 2007 - 07:14 am, by: David Vaughan(Davidv)
There is no problem with humidity from having windows open. An A/C unit comprises two heat exchangers and a compressor/pump. One heat exchanger is at the front of the car and always has air passing over it. The other heat exchanger is in the cabin and receives fresh or recirculated air depending on whether you have the vent open or closed.
Opening the windows merely renders the A/C inefficient by adding presumably hot air to the air the A/C unit has cooled for you. Therefore, you will be warmer and will use more petrol as the A/C tries to compensate by blasting in a higher quantity of cooled air for a longer period (i.e. you use the compressor more).
Cracking open the sunroof adds an air escape slot which speeds up removal of hot air from the cabin when you first get in to the car. Alternatively, it is common and sensible to open the windows wide if your car is hot, to dump the hot air quickly and then close them and run the A/C on recirculate for a while for faster cooling of the interior.
I have noticed that the Soarer system likes to hang on to the recirculation mode for much longer than my other car. If you want fresh air then just override it by pressing the vent open button. This will not affect any other aspect of its operation, although it will leave fresh/recirculate mode under manual control until you next start the car.
Sunday, January 21, 2007 - 07:48 am, by: Peter Nitschke(Pen)
The moisture in the air in the cabin condenses on to the internal exchanger as it is much colder. This then freezes if the A/C is working well.
Having the window open on a humid day would mean more water collection, thus more ice which could reduce the effectiveness of the system as it reduces or blocks the air flow. I haven't looked at one, but possibly if enough ice built up, it might put undue pressure on the fins etc.?
Sunday, January 21, 2007 - 08:12 am, by: David Vaughan(Davidv)
I doubt any of that would happen, Peter. How does the air through the window reach the heat exchanger if it is not on recirculate? If it is not on recirculate then external air is exactly what it is getting anyway. Having the window open and recirculate on just means it gets less of the same air than if recirculate were off. The air through the window is no different from the air through the vent. Further, it will not freeze on the heat exchanger except very briefly. The system will adjust the blower and switch the compressor to account for the fact that air entering the cabin is now around zero degrees, which is probably cooler than you want it. If it is not cooler than you want it then that means the air incoming to the heat exchanger is hot and will melt ice promptly.
It is well known that during rain on otherwise cold days the most effective way of clearing mist from the inside of your windscreen it to run the air conditioner. This leads to no problems, yet it is vastly more likely that freezing will occur during 100% humidity and low temperatures than on a hot and probably dry day.
The air conditioner in our house has its internal heat exchanger under the roof and an external one down the back yard. In hot conditions when there is imminent rain we do not expect ice formation in the ceiling space although we do get a little water runoff out the drain pipe from moisture condensed out of the air. On the reverse cycle, we get ice formation on the external heat exchanger only when the air temperature is near zero; hardly the conditions in which one runs cooling in the car.
Sunday, January 21, 2007 - 05:05 pm, by: Benny Gammelmark(Oldfield)
We once had a table tennis table top leaned up against the Reverse cycle A/C in the house in winter (the side where the fins were). It resulted in the unit freezing up completely and no hot air coming out at all.
As soon as we removed the table top it disappeared.
Sunday, January 21, 2007 - 05:22 pm, by: David Vaughan(Davidv)
When the air temperature drops toward 0 C then reverse cycle A/C no longer produces more output heating than input energy and below zero it is pretty useless as you say, We have a 12KW supplementary heater in the system to cope with the fact and isn't that an expensive thing to run when it is used. Staying under the doona until the sun warms the air a bit, before starting up the heating, is both cheaper and more satisfying
Sunday, January 21, 2007 - 09:08 pm, by: Adam Barry(Acdchook)
David Vaughan wrote on Sunday, January 21, 2007 - 05:22 pm:
When the air temperature drops toward 0 C then reverse cycle A/C no longer produces more output heating than input energy
Well if it ever DID produce more output heat energy than input energy it would violate the First Law of Thermodynamics, as energy would not be conserved.
Sunday, January 21, 2007 - 09:31 pm, by: David Vaughan(Davidv)
Common misconception, Adam. You understand the laws but have not fully considered the nature of the system under discussion.
The laws of thermodynamics are not violated because the input energy to the system is not the energy which heats or cools you. The system is a pump, not a heater. It pumps heat rather than, say, water. Superficially, the home system puts out twice the heat that it consumes but in reality it consumes all of its inputs and uses enough of it to pump a greater amount of heat between sources and sinks which are external to the pump itself. The input energy contributes no direct heating or cooling. Even if we could somehow capture some of the pumped heat and use it to drive the pump, the heat source (from where we pump it) becomes part of the system under analysis and it will be found that the Second Law rules there also.
Sunday, January 21, 2007 - 10:11 pm, by: Brian Timms(Turbo_brian)
Simple answer, yes, I did it today after some low-lifes smashed my driver's window to break into my car, so no driver's window, 42 degrees, and air con blasting at full pelt, needless to say it cooled me 5 or so degrees cooler which was good, but didn't make the car cold.
And I had the unit on for a good 5 hours without it freezing up or seeming to cause issues.
Monday, January 22, 2007 - 02:09 am, by: Chris Prak(Carizma)
Yeah of course you can run your air-con while the windows are open... it's just this: You use your air-con on hot days, so when you open your windows, the cold air coming out of the air-con ducts will get sucked out and hot air will come belting in, so this just defies the point of having the air-con on while windows are open as this does jack all and waste of cool air-con air. Have it on recirculation with windows closed, or if you must, a tiny 1cm gap if you have a smelly car.
Tuesday, January 23, 2007 - 04:19 pm, by: Damien Barnes(Barned01)
while we are on the subject of this, SA has experienced a plethora of 34+ degree days lately. When using the A/C after the car has been sitting in the sun all day, it never quite seems to cool the car down. It takes the 'heat' out of the air but it is still far from the 'cold' display that the screen is telling me (which should be <22 degrees), even after 30 minutes of driving, the car never really gets down to a cold temparature (i would say it would easily stilll be above 28 in the cabin). this is with A/C on, recirc, highest fan setting, windows up (initially down to remove the blast of hot air), and 'cold' setting
If the A/C is used in say 28 degree weatheer (later in the night say) THEN the car starts to cool down and you can notice a discernable drop in temperature after 3 or 4 minutes.
Is the A/C normally more efficient than what we are experiencing? is it an A/C issue, is it a gas issue, is it a whinging person that should just shut up issue? cheers Barnsey
Tuesday, January 23, 2007 - 07:52 pm, by: David Vaughan(Davidv)
Like Peter, I suspect low gas. It sounds as though your system can not pull a large differential in the temperature. However, it may be a characteristic of the Soarer A/C control. I have noticed that in the Soarer I drive at 23 during hot days over long periods but turn it up to 24 at night or in milder conditions. In the IS300 I never vary it from 24 in any external conditions.
Wednesday, January 24, 2007 - 01:18 am, by: Benny Gammelmark(Oldfield)
Mine tends to get colder the longer I drive it. It seems like the area around the temp. sensor gets warm. I often have to turn up the heat after driving a long time on a cold night.
On the question of your problem Damien, see the above posts
Wednesday, January 24, 2007 - 11:14 am, by: Damien Barnes(Barned01)
gas was my first thought, but considering my main drive is an RA40 celica where aircon consists of clockwise rotation of my hand on a lever on the door card, I didn't know what the symptoms were of a 'gas' issue.
There is no dash mat although i did notice a lot of dust, i will check the sensor on the passenger side (I assume it is that little thing right up against the windscreen where the A Pillar comes down?) and have a look at the cabin temp sensor (I assume you are talking about left knee when in the drivers seat?) and borrow my GF's hairdryer to adjust the temperature Failing that, I will see an aircon person to see what they say about my 'gas' issues. Cheers guys
Hey peter (OT) how did the timing belt tutorial thingy i sent you go, did you need any more stuff or a different format?
Wednesday, January 24, 2007 - 05:12 pm, by: David Vaughan(Davidv)
Damien, the temperature sensor is on the dash to the left of the steering wheel, low down. There is a small plastic grill a bit over 1cm square. The sensor on top of the dash on the left looks for sunlight and boosts the A/C when you move out of shade into sun to anticipate temperature changes. That is why you should avoid having your rego sticker low down on the left side of the front window.
Thursday, January 25, 2007 - 09:32 am, by: Damien Barnes(Barned01)
ok found the little plastic grille thing last night...it was full o' dust, so one would assume a proper reading wasn't getting to it, have brushed that out now, test will be on the way home today. Next is to check this AC gas sight glass thingy near the battery, what am i looking for (in terms of inside the glass thing, not the glass thing itself)? the fact i can see gas inside it...which i assume would be a fluro green colour?
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