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Discussion Starter · #1 · (Edited)
The G2's literature states that all models except the RT feature a "Tri-Zone Automatic Climate Control System with Humidity Control and Air Filtration".

Neither Honda's website nor the manual has any explanation for what the "humidity control" function of the climate control system does (aside from the obvious control of humidity in some way). After some research, it appears this feature began its life some years ago in the Acura MDX and later spread to other models including Hondas.

Below is an except from a book I found on the subject. I apologize on behalf of the author for his writing style and grammar - to me, it is difficult to read and understand.

"Frank Paluch, a Honda R&D president […], asked his research colleagues to pitch some as yet untried technologies that they had been working on to spruce up the vehicle. Among the ideas that were presented, an automatic humidity control system was particularly intriguing, although at first it appeared to be a bit low tech.

The concept was intended to solve a common drivers, which Paluch described vividly for an audience of engineers in upper Michigan: "Imagine yourself here in Traverse City in the winter months. The snow you kick off your shoes inside your vehicle melts overnight in your heated garage, soaking the mats. The next morning you get in your car and drive out into the cold. As soon as the outside air hits the windshield, humidity fogs the inside of the glass. You hit the defrost button. Your eyes dry out, the noise is loud, and the heat is pointed to the windshield instead of keeping your feet warm.”

In addressing this annoying problem, Honda R&D had two goals: Improve driving satisfaction and also greater fuel efficiency by minimizing the drag on the powertrain imposed by always-on auto AC systems – the primitive solution provided in most cars to reduce humidity levels and fogging. Combining hardware and algorithms, the R&D team had devised a system that could detect temperature and humidity levels outside and inside of the car and automatically start to bleed warm or cold air to the windshield before condensation occurs. Or, to extend Paluch’s example, the vehicle’s mats would still be soaked, but the car would be warm and the glass clear. Moreover, the system turns off the compressor when the AC is not needed, potentially decreasing fuel consumption by as much as 4%.

"It spoke to a critical customer issue and a novel way," Paluch said. "However, upon first hearing about it, it seemed to all of us on the team to be an innovation too limited for the added expense of putting it in the car. So we rejected it."

Not satisfied with that answer, Honda’s researchers installed the humidity control system into a previous generation MDX to demonstrate the concept. The researchers poured water over the floor of the vehicle, placed it in a humidity chamber overnight, and made plans to meet the MDX development team at 5 AM the next morning. Seven MDX member showed up, piled into the vehicle, and drove off.

The SUV’s windshield fogged up instantly; then the researchers turned on the climate system. Within seconds, the glass had cleared, while the temperature and humidity inside of the car remained at comfortable levels. This exercise was repeated the next day in an MDX without the humidity control equipment. That car was undrivable, no matter how long the defroster remained on."

Rothfeder, Jeffrey. Driving Honda: Inside the World's Most Innovative Car Company. New York: Portolio / Penguin, 2015. Paperback.
 

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2006 Ridgeline RTS in Steel Blue
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Nice Find ZRog, It may also be beneficial in these Humid Climate issues with the Airbag stuff, although hopefully they have stopped using Amoinum Nitrate in the inflators
 

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2019 RTL awd, MSM
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That would be awesome to have on the G2. My wife's '08 Accord has the condensation problems at certain times of the year, very foggy windows unless you keep it on max defrost all the time.
 

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Discussion Starter · #6 ·
Decades ago, I realized automatic climate control systems that run the compressor at all times (unless it was near or below freezing outside) needed improved logic. If it's 40ºF outside and dry, it's wasteful to run the compressor to cool and dehumidify the air then heat it immediately after it is cooled and dehumidified only to remove even more moisture from it! This is hardly different than running the A/C in your house in the winter and using additional heat to offset it. Your utility bills would be exorbitant and the air would be so dry you'd end up with health problems. But, this is exactly what most automatic climate control systems do!

Since there have traditionally been no humidity sensors used, the climate control system must assume that humidity is always high (for safety) and must run the compressor even when it''s cool and dry. The addition of a humidity sensor allows the system to stop compressor use when cooling and dehumidification are not necessary, thereby improving comfort, performance, and efficiency.

Automotive climate control systems are somewhat different than residential/commercial building systems. In automotive systems, the compressor cycles (or varies its displacement in a few models) to maintain a constant evaporator temperature just above freezing. It then uses actuators and mode/blend doors to control the air flow path and temperature. Outlet temperature is adjusted by heating the cooled air - this is a huge waste when outside temperature is more than a few degrees below the desired interior temperature! Enclosed building systems cycle the compressor to maintain a constant room temperature. Maintaining a constant evaporator temperature is easier since the temperature and quantity of air passing through the evaporator are more constant, so a simple orifice to regulate evaporator temperature is sufficient (although, you can increase efficiency further with variable speed blowers and compressors and thermal expansion valves).

The next step in efficiency will be variable-speed electric compressors that are independent of engine RPM for longer life, more comfort, and better efficiency, although at a higher cost than current engine-driven compressors. These compressors currently exist in plug-in EVs and some hybrids.
 
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