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Yay. Something else to obsess over. I need a hobby, haha! A couple of days ago, I decided to take my calibrated Fluke thermometer along for a ride to see how accurate the climate control was. Bad idea. I tried a few locations for the thermocouple (temperature sensor) including inserting it into the aspirator tube below the steering wheel where the in-cabin air temperature sensor is and near the center console. I found that the actual air temperature inside the cabin was about 8 degrees F (or more) higher than the setting on the climate control. On the "Lo" setting, the outlet temperature was about 44 degrees. The outdoor temperature was in the 90s at around 45% relative humidity. No complaints with the system's ability to cool, but I'm surprised (and disappointed) with the variation between set point and actual temperature. I drove around for over an hour giving the system plenty of time to settle out. Perhaps other vehicle's climate controls are the same way - I've never actually tested one until now. I suppose there is a possibility this is an intentional design so that the occupant's "feels like" temperature is closer to the climate control setting due to the circulation of much colder air coming from the vents. This might very well be the case considering when I adjusted the climate control to 66 (to compensate for the 8 degree difference and the fact I'm most comfortable at 74), I was feeling a bit on the chilly side after a while.
 

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I set it for whatever feels comfortable to me at the time, regardless of what the value may be. It certainly may deviate some from my own experience in other environments.

What I do like about it is that it changes temp fairly quickly, and in the RTL seems to do a decent job of distributing 2 different settings out of opposite sides of the dash.

I know when they do a basic temp test to determine if there is enough cooling from the system, sensors are put right on the vents. So you are right, by the time it gets to the passengers it will be quite a bit warmer, and considering the 'greehhouse' enviroment it needs to condition, it is not too surprising. So I suspect the actual values they come up with are averaging to a large extent to take all that into account.
 

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Yay. Something else to obsess over. I need a hobby, haha! A couple of days ago, I decided to take my calibrated Fluke thermometer along for a ride to see how accurate the climate control was. Bad idea. I tried a few locations for the thermocouple (temperature sensor) including inserting it into the aspirator tube below the steering wheel where the in-cabin air temperature sensor is and near the center console. I found that the actual air temperature inside the cabin was about 8 degrees F (or more) higher than the setting on the climate control. On the "Lo" setting, the outlet temperature was about 44 degrees. The outdoor temperature was in the 90s at around 45% relative humidity. No complaints with the system's ability to cool, but I'm surprised (and disappointed) with the variation between set point and actual temperature. I drove around for over an hour giving the system plenty of time to settle out. Perhaps other vehicle's climate controls are the same way - I've never actually tested one until now. I suppose there is a possibility this is an intentional design so that the occupant's "feels like" temperature is closer to the climate control setting due to the circulation of much colder air coming from the vents. This might very well be the case considering when I adjusted the climate control to 66 (to compensate for the 8 degree difference and the fact I'm most comfortable at 74), I was feeling a bit on the chilly side after a while.
When my truck was brand spanking new I could adjust the thermometer and sense the change in temperature about every 2 degrees or so. Now, over 5 years later, the A/C only puts out cold air once it is set on "Lo". Anything above low only produces kind of luke warm/barely cool air. This is annoying but I pretty much ignore it now. The dealer has checked this several times but the results show the A/C and heater are working within the acceptable ranges and to have a nice day.

The first truck I owned was a beater '81 GMC Sierra 3-speed (w/ broken overdrive) and a 2-65 HVAC unit. Two windows down at 65 mph!!!!! so this RL is a huge step up from that...even with a not so accurate gauge.
 

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No, it doesn't. Why?
Human skin responds pretty quickly to air currents that suck away heat. So the temperature as measured by your probe (absolute temp) probably doesn't match the perceived temperature that people feel.

Chip H.
 

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Discussion Starter #7
Human skin responds pretty quickly to air currents that suck away heat. So the temperature as measured by your probe (absolute temp) probably doesn't match the perceived temperature that people feel.

Chip H.
I'll buy that - to some degree... However, at "room" temperatures where most people are comfortable and low wind speeds, you're in sort of a "neutral" zone between wind chill and heat index where neither is a significant factor. The ceiling fan in my living room exposes me to similar wind speeds encountered in my vehicle considering I adjust the vents so they do not expose me to the direct flow. If I set my home thermostat on 74, then the house cools (or heats) to 74. I would expect/prefer the same in a vehicle.

I know there are a few vehicle climate control systems out there that have infrared thermometers that use passengers' skin temperatures as an input to the climate control system. I seem to recall Jeep having this feature in the Grand Cherokee in the late 90s.

Another annoyance is the linking of the GPS with the climate control. Both my '07 and '10 had annoying, dramatic changes in blower speed as a result. My understanding is that the system will increase cooling capacity where needed depending on information from both the sunload sensor and the actual vehicle position in relation to the solar angle as calculated by the GPS signal. The problem is that when the system is in cooling mode and is close to setpoint, it will always increase blower speed and decrease temperature on the driver's side when the driver's side is in the shade - almost like it's 90 degrees off!

These observations make me question just how much time and accuracy goes into engineering these types of systems and wonder how much benefit is actually realized from such features. Honestly, it makes more sense to me for the system to tweak settings based only on one or more sunload sensors since the GPS method can't determine when you're driving through a tunnel, in the shadow, or it's cloudy outside. I'd gladly give up the GPS link in exchange for an actual humidity sensor! :) Honda was starting to get the right idea with the humidity control that recently appeared in the Crosstour, although it seems to be marketed as more of a fuel-saving technique (by turning off the compressor to reduce dehumidification when it's not needed) than a comfort feature.
 

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Great point about a humidity sensor. I don't have navi so I don't have the GPS link. I had it on my 02 MDX. Maybe it is just another 'Honda thing' that never goes away. I remember the random changes in fan speed, which did not always seem related to how warm or cool I was feeling at the time.
I suppose these systems are designed with an empty passenger cabin, and then they model in a given number of people (another factor). Sensors at each sitting position to determine air flow and hot spots, etc.
Sounds like a lot of compromises being made if you factor in all the variables being involved. I think getting the air flow right is probably one of the most critical. On some of the warmest days when driving into the sun, it seems the fan speed should be higher in the 'auto' mode. Maybe it would be if I had the GPS link. Then again......
 

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Discussion Starter #9
There is a setting in the navi's diagnostic menu called "fan control" that can be toggled on or off. It makes sense that this should enable or disable the navi's ability to change the blower speed, but the system doesn't appear to behave any differently whether this setting is on or off. It could be a "dead" button - meaning it was put in during development, but ended up not having a functional purpose and was never removed from the user interface. I also considered it might be related to blower speed and voice commands. My G35 would instantly lower the blower speed while listening for voice commands, but again, neither setting made any difference in the blower speed.
 
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