I have been complaining about the stupidity of late model car environmental controls for 10 years now. I have sent detailed "bug reports" and fixes to the manufacturer only to be told that "the system is operating as designed". Obviously the problem is that it was designed to spec without actually being looked at from a systems viewpoint.
One pervasive fault is the divergence from older manual eviro control functionality when applying microcontrollers to the task. Older cars would handle defogging by running the AC compressor until the coil temperature approaches the freezing point where it would then cut out. When defogging, it's critical that the compressor runs no matter what the cabin temperature setting is. Late model cars have the AC compressor tied directly to the cabin temperature setting and sensor. This causes the humidity that was captured during cool down to start evaporating back into the cabin as soon as the cabin hits its target temperature. Stupid. Period.
The old method of running the compressor, condensing out humidity, while heating is the most effective way to deal with the situation. Instead, because the new systems perform so poorly, they do things like switch to outside air to try to make up for a poorly thought out design and implementation.
I agree, Rob. It's like the analog volume control knob on the stereo--sound control is an analog thing so that works better to the tuned ear than a series of preprogrammed steps. In this case, it's not linear but interactions that, apparently, require subtleties. I don't get why these functions were automated in the first place.
Good point, Ann. I agree the automated systems may not deliver much value. I don't find it that difficult to manage the cooling and heating system in my older vehicle. There are subtleties to the system that can only be managed manually.
I am only an electrical engineer, but it seems the right logic to me. Each pass through the refrigeration unit drops the temperature by say, 10 degrees so it seems to me that you can achieve a much lower temperature and much quicker than by trying to cool air at a fixed temperature from outside. Aslo if the air is humid you can remove that much more moisture by working on the same air volume repeatedly. That is how I find it most effective.
Later when cool, the switch to fresh air is necessary to allow oxygen into the cab. Secondly the air is cooled in a small percentage in comparison to the volume of the cab so th A/C can cope, but my experience on really hot days (95degF and up) is that it only really maintains the temperature at a low enough value on recirculate.
I would also be interested in the fan speed that Toyota chose. It seems to me that the air conditioning is less effective at high fan speeds. My theory is that the air does not get enough time to cool down as it passes through the refirgeration unit.
From my experience the external air in the cold is to reduce the misting of your breath. I have a problem when I don't drive very far and the car hasn't had a chance to warm up where the air condenses and then freezes on the inside of the windshield.
This looks like yet another pointless automation of a car system that should always be user-controlled or at least user-controllable. My car, thankfully, is old enough that I can decide which mode I want to be in, combined with how much airflow via fan control and whether that air is heated or cooled.
The Highlander is not that old a car model so this one really seems baffling. What could possibly have driven the Toyota engineering team to design the automated climate controls in that manner? If there a glitch with your particular car or is this just a greater design flaw in the model or perhaps with the Toyota car platform in general?
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