Have a question.
When I press the 'Auto' button on the climate system, the AC light comes on automatically. Does this indicate that the AC is always running, even when it does not have to (e.g., when I need some warm air), or does it mean that the system will turn on the AC when it feels like it needs to (e.g., when it needs to cool the inside)?
Thanks.
When I press the 'Auto' button on the climate system, the AC light comes on automatically. Does this indicate that the AC is always running, even when it does not have to (e.g., when I need some warm air), or does it mean that the system will turn on the AC when it feels like it needs to (e.g., when it needs to cool the inside)?
Thanks.
Lead Lap
I like the auto feature, however, I dont' like to have AC running all the time. Is there a Cbest setting for that where you can run auto mode, but it will detect the temp and turns AC off?
Pole Position
When that light is on it means that the entire system airflow is being chilled by the A/C system evaporator, the A/C compressor itself will/might only run intermittently, enough to keep liquid refrigerant available at the evaporator inlet so its temperature will remain continuously at about 33F. There are now some new varible displacement compressors that do run continuously, but with zero displacement if no flow is required.
The system airflow is first chilled in this manner in an effort to reduce its temperature to dewpoint and thus condense any airborne moisture molecules onto the evaporator surfaces.
After leaving the evaporator core some or all of the now cold airflow is passed through the heater core to reheat to your desired comfort level.
Up until about ten or fifteen years ago the A/C sysetm was almost never run automatically if the outside temperature was already cool enough to provide the human comfort level desired. But for quite some time it had been well known that even at lower temperatures, down to about 45 degrees F, the system could be used efficiently to dehumdify the system airflow and thus help remove and prevent window and windshield fogging.
So it became quite common for the A/C system to be automatically activated when the system was put in defrost/defog/demist mode.
I can only make a "wild card" guess at why (NipponDenso)automotive engineers decided, with the "cards" stacked VERY heavily against them, to try and use the A/C system, EXCLUSIVELY, to prevent window and windshiedl fogging. Notice I did not say "remove" windshield and window fog, more about that later.
In about 1993 I rented a Jaguar from Budget at Logan airport. It was very cold that night and raining, and the rain was freezing as soon as it touched any cold surface, such as the windshield of that Jaguar. We had about a twenty mile drive ahead of us, and the only way we could keep the windshield cleared was to have the heat full up and all of the airflow routed to the windshield.
Clearly a very personally discomforting circumstance.
Lexus is a Luxury car line. How many people buying this class of car would complain of the discomfort of hot airflow to the windshield, and thus to their face and upper body, in these circumstances?
Most likely ALL ??
It is very likely that someone has analyzed the actual, or true need for defrost/defog/demist, and determined that in this particular class of vehicle most owners never encounter a climate severe enough to warrant concern.
So, they decided to find some way to be more unobtrusive, less discomforting, to the owners of these vehicles on the seemingly rare occassions when some serious level of defrost/defog/demist was needed.
But, heat exchangers are not very efficient unless the two mediums have greatly disparate temperatures. And here we have a circumstance wherein the A/C evaporator cannot be chilled below freezing, and the airflow to be dehumidified is below 50F, only an 18 degree F MAXIMUM difference.
Lexus has designed their cliamte control system such that it continues to attempt to dehumdify incoming airflow all the way down to about 35F.
How do they do that?
An extremely dense and complex evaporator, 10,000 square inches (in a 92 LS)of cooling surface, designed such that a great deal of turbulence is created in the airflow as it passes over the cooling vanes.
Extremely LOW system airflow. The longer it takes for the air to move through the evaporator core the colder it will get. But how do you limit the inflow? You limit the exit airflow path, the path from the vehicle, to the absolute minimum requied by the US government.
And if the government isn't watching ?? !!
Several problems arise from this.
That A/C evaporator is now so dense it almost acts like a sponge!
Sponges don't "release" the water they hold unless you sqeeze it out or if the vapor pressure is so high that the moisture trapped in its cells evaporates away quickly. Lots of HOT and DRY airflow.
Quickly, ahh, there's the rub.
Some of us are old enough to remember that this whole mold and mildew smell coming from the system vents was a lot rarer as little as ten years ago. When you use the A/C system to dehumdify the system airflow most, but not all, of the mositure condensed will run out the drain tube. When the overall night time temperature is below 55-60 degrees F or so, some of this moisture will remain within the evaporator core for days and days. And remember that especially dense and complex Denso evaporator, it will hold an "extra" level of this mositure.
So, don't be too surprised if your Lexus starts to smell of mold and mildew sometime this winter, and don't be too surprised if your windshield fogs up suddenly in your early morning drive, and don't be too surprised if your windshield starts to fog over again shortly after you cycle the defog mode off, and don't be too surprised if you windshield starts to fog over as you climb up a mountain pass this winter.
Did I miss anything?
Oh, yes, if all else fails, use the tried and true method, ONE THAT ALWAYS WORKS to remove fog from your windshield BLAST IT WITH HEATED AIRFLOW!
The system airflow is first chilled in this manner in an effort to reduce its temperature to dewpoint and thus condense any airborne moisture molecules onto the evaporator surfaces.
After leaving the evaporator core some or all of the now cold airflow is passed through the heater core to reheat to your desired comfort level.
Up until about ten or fifteen years ago the A/C sysetm was almost never run automatically if the outside temperature was already cool enough to provide the human comfort level desired. But for quite some time it had been well known that even at lower temperatures, down to about 45 degrees F, the system could be used efficiently to dehumdify the system airflow and thus help remove and prevent window and windshield fogging.
So it became quite common for the A/C system to be automatically activated when the system was put in defrost/defog/demist mode.
I can only make a "wild card" guess at why (NipponDenso)automotive engineers decided, with the "cards" stacked VERY heavily against them, to try and use the A/C system, EXCLUSIVELY, to prevent window and windshiedl fogging. Notice I did not say "remove" windshield and window fog, more about that later.
In about 1993 I rented a Jaguar from Budget at Logan airport. It was very cold that night and raining, and the rain was freezing as soon as it touched any cold surface, such as the windshield of that Jaguar. We had about a twenty mile drive ahead of us, and the only way we could keep the windshield cleared was to have the heat full up and all of the airflow routed to the windshield.
Clearly a very personally discomforting circumstance.
Lexus is a Luxury car line. How many people buying this class of car would complain of the discomfort of hot airflow to the windshield, and thus to their face and upper body, in these circumstances?
Most likely ALL ??
It is very likely that someone has analyzed the actual, or true need for defrost/defog/demist, and determined that in this particular class of vehicle most owners never encounter a climate severe enough to warrant concern.
So, they decided to find some way to be more unobtrusive, less discomforting, to the owners of these vehicles on the seemingly rare occassions when some serious level of defrost/defog/demist was needed.
But, heat exchangers are not very efficient unless the two mediums have greatly disparate temperatures. And here we have a circumstance wherein the A/C evaporator cannot be chilled below freezing, and the airflow to be dehumidified is below 50F, only an 18 degree F MAXIMUM difference.
Lexus has designed their cliamte control system such that it continues to attempt to dehumdify incoming airflow all the way down to about 35F.
How do they do that?
An extremely dense and complex evaporator, 10,000 square inches (in a 92 LS)of cooling surface, designed such that a great deal of turbulence is created in the airflow as it passes over the cooling vanes.
Extremely LOW system airflow. The longer it takes for the air to move through the evaporator core the colder it will get. But how do you limit the inflow? You limit the exit airflow path, the path from the vehicle, to the absolute minimum requied by the US government.
And if the government isn't watching ?? !!
Several problems arise from this.
That A/C evaporator is now so dense it almost acts like a sponge!
Sponges don't "release" the water they hold unless you sqeeze it out or if the vapor pressure is so high that the moisture trapped in its cells evaporates away quickly. Lots of HOT and DRY airflow.
Quickly, ahh, there's the rub.
Some of us are old enough to remember that this whole mold and mildew smell coming from the system vents was a lot rarer as little as ten years ago. When you use the A/C system to dehumdify the system airflow most, but not all, of the mositure condensed will run out the drain tube. When the overall night time temperature is below 55-60 degrees F or so, some of this moisture will remain within the evaporator core for days and days. And remember that especially dense and complex Denso evaporator, it will hold an "extra" level of this mositure.
So, don't be too surprised if your Lexus starts to smell of mold and mildew sometime this winter, and don't be too surprised if your windshield fogs up suddenly in your early morning drive, and don't be too surprised if your windshield starts to fog over again shortly after you cycle the defog mode off, and don't be too surprised if you windshield starts to fog over as you climb up a mountain pass this winter.
Did I miss anything?
Oh, yes, if all else fails, use the tried and true method, ONE THAT ALWAYS WORKS to remove fog from your windshield BLAST IT WITH HEATED AIRFLOW!
Pole Position
In my 92 LS400 Lexus would open the A/C compressor circuit if the OAT (Outside Air Temperature) sensor indicated that the OAT was below about 35 degrees F. I simply designed a circuit wherein I could manually switch a resister in series with this sensor during the colder months such that at 47 F the A/C ECU "thought" the OAT was below 35F.
Design did not work with my 2001 RX because the temperature sensor downstream of the evaporator is now the only one used to open the A/C compressor circuit. But no sweat I said, I'll justpay more careful attentyion and turn it off manually every time the idiot thing turns it on.
WRONG!
The idiot thing out-smarted me. When I use the defrost/defog/demist function it automatically turns on the A/C compressor without any indication of having done so, and cycling the button on then off has no effect.
So the only quick way I could find to "out-smart" this idiot was to remove the compressor clutch relay.
I'm meeting with an electronics engineer this very evening to see if you can come up with a circuit that disables the A/C compressor when the OAT is below 50F.
Design did not work with my 2001 RX because the temperature sensor downstream of the evaporator is now the only one used to open the A/C compressor circuit. But no sweat I said, I'll justpay more careful attentyion and turn it off manually every time the idiot thing turns it on.
WRONG!
The idiot thing out-smarted me. When I use the defrost/defog/demist function it automatically turns on the A/C compressor without any indication of having done so, and cycling the button on then off has no effect.
So the only quick way I could find to "out-smart" this idiot was to remove the compressor clutch relay.
I'm meeting with an electronics engineer this very evening to see if you can come up with a circuit that disables the A/C compressor when the OAT is below 50F.
Wow, Willard. That was quite infomative. Somewhere in there was the answer to "Do we turn off the AC (after Auto mode is engaged) if we are not trying to cool anything?".
I just thought you can post a short answer before I reread/analyze you post in more detail.
I just thought you can post a short answer before I reread/analyze you post in more detail.
if you want to have just AIR and not AC, just go into the CLIMATE menu and set the fan power instead of pushing AUTO. That will turn the A/C on.
That's for NAV vehicles.
That's for NAV vehicles.
Guest
I hate the A/C-all-the-time thing too, but what I do all winter is just start the ventilation system with the FAN switch, so the A/C doesn't come on. As you guys have probably noticed, the system is ALWAYS in auto mode for the temperature, even when off (you can feel warm air in winter if you have the system in "fresh"). I always have the system either in "off" or in fan at No. 1 (very mild winters and low humidity here).
If I ever need to defog (once a year, or so), just press the defog (or auto) and the compressor is fully operational.
I agree the auto system should leave the A/C compressor "off" below 65º or so. If you need to defog, that mode always engages the compressor, so why run it all the time? Maybe even design that double-pressing the "auto" switch reverses the A/C default like when you don't want the compressor above 65º, or when you want it below that number. Or even better, being able to adjust the cut-off point; would it be that hard?
Good evening gentlemen.
JC
If I ever need to defog (once a year, or so), just press the defog (or auto) and the compressor is fully operational.
I agree the auto system should leave the A/C compressor "off" below 65º or so. If you need to defog, that mode always engages the compressor, so why run it all the time? Maybe even design that double-pressing the "auto" switch reverses the A/C default like when you don't want the compressor above 65º, or when you want it below that number. Or even better, being able to adjust the cut-off point; would it be that hard?
Good evening gentlemen.
JC
Driver School Candidate
I may be missing the point here but my advice would be to let the compressor run, even in the winter. I have a friend with an A/C shop in Florida and most of his work is from people that don't run their A/C during the winter (only 2 or 3 months here of course ) and find out it doesn't work when they need it in the spring/summer. Most times it's because the refrigerant and oil is not circulated for months and gaskets, o rings dry out and start leaking.
Wow, this basically describes everything I hate about my car's HVAC system - that it was designed for warm climates, that it has a mind of it's own. I live in a cool/freaking cold climate and I never use the AUTO mode. In winter I leave it at 30C and defrost/feet mode. Thanks for the in-depth analysis.
Lexus Fanatic
Quote:
that isnt even true....Originally Posted by wgreene63
I may be missing the point here but my advice would be to let the compressor run, even in the winter. I have a friend with an A/C shop in Florida and most of his work is from people that don't run their A/C during the winter (only 2 or 3 months here of course ) and find out it doesn't work when they need it in the spring/summer. Most times it's because the refrigerant and oil is not circulated for months and gaskets, o rings dry out and start leaking.
the refrigerant/oil are ALWAYS present and your O-rings dont dry out/leak from not using the system in the winter. who tells you this stuff?