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Discussion Starter · #1 ·
Twice this weekend, at highway speed, I noticed the cabin temperature got much colder compared to non-highway driving.
It was about 30-40°F both times, with the heat set up at 72 AUTO (recycle off). I was quite toasty before getting on the highway but then once at high speeds it was significantly colder. I actually had to crank the heat to 80°F (!) to feel hotter. Seemed like any setting between 72 and 80 wouldn't do much. I also noticed the air around my leg was hotter, but the top vents were blowing almost cold air.
 

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Super-old looking diagram (LOL) but the basic technology is the same. Fresh air enters thru inlet, gets heated at the heater casing/radiator connection, and exits to cabin thru the foot well and face vent outlets. There's more cold air intake at higher speeds and less time for that cold air to linger near the heating element, so the outlet air feels cooler. The outlet air flows 'easier' (and has less distance to travel) thru the larger foot vents versus smaller face vents.
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In Auto climate control mode, there are two interior sensors that monitor temperature. The lower sensor is kind of angled in a way that would pick up the heat from the foot-well vents, so might make the Auto control 'think' the cabin is warmer than it is. (Maybe the Auto system would eventually catch up, but it will take a while? Or maybe covering this sensor would make the Auto system respond faster?) Increasing the temperature set point adjusts the flaps/blend to let heat into the cabin more quickly.
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I tend to use just passive heating and look forward to high speed highway stretches for bursts of cabin warmth. With passive heating, it's quite cold in regular driving and warms up once at highway speeds... inverse conditions from actively using the climate control system.

 

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I noticed the same, but I use recirculate (it doesn't get cold enough here in FL to notice the difference). Last night I was getting food for my kids at McDonalds and noticed the engine was running (it actually got below 40 last night) then noticed it was pulling air from outside. I put recirc on and the engine shut off immediately.. I think recirculating the warm air is just like recirculating cold air during the summer (more efficient).. Tell me (I wouldn't know) - in very cold climates, is it necessary to pull air from outside??
 

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Discussion Starter · #4 ·
Super-old looking diagram (LOL) but the basic technology is the same. Fresh air enters thru inlet, gets heated at the heater casing/radiator connection, and exits to cabin thru the foot well and face vent outlets. There's more cold air intake at higher speeds and less time for that cold air to linger near the heating element, so the outlet air feels cooler. The outlet air flows 'easier' (and has less distance to travel) thru the larger foot vents versus smaller face vents.
View attachment 6236
View attachment 6240
In Auto climate control mode, there are two interior sensors that monitor temperature. The lower sensor is kind of angled in a way that would pick up the heat from the foot-well vents, so might make the Auto control 'think' the cabin is warmer than it is. (Maybe the Auto system would eventually catch up, but it will take a while? Or maybe covering this sensor would make the Auto system respond faster?) Increasing the temperature set point adjusts the flaps/blend to let heat into the cabin more quickly.
View attachment 6237
I tend to use just passive heating and look forward to high speed highway stretches for bursts of cabin warmth. With passive heating, it's quite cold in regular driving and warms up once at highway speeds... inverse conditions from actively using the climate control system.

Interesting. What about sun hitting the top sensor? Would that mean less heat @ top vents and more heats @ feet?
 

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Discussion Starter · #5 ·
I noticed the same, but I use recirculate (it doesn't get cold enough here in FL to notice the difference). Last night I was getting food for my kids at McDonalds and noticed the engine was running (it actually got below 40 last night) then noticed it was pulling air from outside. I put recirc on and the engine shut off immediately.. I think recirculating the warm air is just like recirculating cold air during the summer (more efficient).. Tell me (I wouldn't know) - in very cold climates, is it necessary to pull air from outside??
With three people in the car it'd say yes! Also there was a huge bag of clean laundry in the rear seats and I'm bothered by scents ;-) Heating/efficiency-wise, probably better to recirculate.
 

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Interesting. What about sun hitting the top sensor? Would that mean less heat @ top vents and more heats @ feet?
Possibly, but I don't think Honda's sensors are that 'smart' where they control different features. My guess is the temperature control loop in Auto averages the reading from the two sensors, to try for a representative reading of the cabin temp. And it will get the temperature 'wrong' as a result, because it's shooting for a middle ground.
 

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I noticed the same, but I use recirculate (it doesn't get cold enough here in FL to notice the difference). Last night I was getting food for my kids at McDonalds and noticed the engine was running (it actually got below 40 last night) then noticed it was pulling air from outside. I put recirc on and the engine shut off immediately.. I think recirculating the warm air is just like recirculating cold air during the summer (more efficient).. Tell me (I wouldn't know) - in very cold climates, is it necessary to pull air from outside??
Recirc with heat on in cold climates can make the cabin get to Florida-like humidity levels, if run long enough. :) The hotter cabin air holds more moisture and can condense to fog up the windows. If I have to run recirc on a cold day, I pulse A/C on/off to help dry out the air.
 

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Recirc with heat on in cold climates can make the cabin get to Florida-like humidity levels, if run long enough. :) The hotter cabin air holds more moisture and can condense to fog up the windows. If I have to run recirc on a cold day, I pulse A/C on/off to help dry out the air.
I always assumed the humidity sensor in the car would sense the higher humidity and run the ac automatically.. BUT if it's cold enough outside, maybe the compressor is unable to run?
 

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I always assumed the humidity sensor in the car would sense the higher humidity and run the ac automatically.. BUT if it's cold enough outside, maybe the compressor is unable to run?
I should clarify that my comments relate to manual operation... but even if/when I run Auto, I tend to press A/C off and manage it myself.

Maybe I'm not giving Honda enough credit (and haven't looked up the parts to cross-check), but I don't think there's a humidity sensor. Or maybe it's combined with the one below the power button? My guess is that when in Auto, the system uses temperature as a proxy to determine what's 'comfortable' and manages the A/C that way (?).
 

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We got lots and lots of humidity here. It may be 45-50 but a dry 25-30 rarely feels as cold. I always use manual heater controls. I frequently change the mode setting (foot, foot + dashboard, or defrost). I mostly run with heater on only when engine is on for battery charging, I turn heater off otherwise. till interior is comfortable, then passive heating to my feet.

I leave the heater's temp. control on Hi, but will lower it to 80 when the air at my feet is too hot.

On very cold mornings I sometimes lower the temp. control to Lo, but keep the heater system off till engine warms up, then go to Hi setting (sometimes faster engine warm-up doing this).
 

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We got lots and lots of humidity here. It may be 45-50 but a dry 25-30 rarely feels as cold. I always use manual heater controls. I frequently change the mode setting (foot, foot + dashboard, or defrost). I mostly run with heater on only when engine is on for battery charging, I turn heater off otherwise. till interior is comfortable, then passive heating to my feet.

I leave the heater's temp. control on Hi, but will lower it to 80 when the air at my feet is too hot.

On very cold mornings I sometimes lower the temp. control to Lo, but keep the heater system off till engine warms up, then go to Hi setting (sometimes faster engine warm-up doing this).
Do you adjust this approach while on highway, or notice the difference in upper/lower vents @pasei mentions above while on highways?
 

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Do you adjust this approach while on highway, or notice the difference in upper/lower vents @pasei mentions above while on highways?
I use the same approach on the highway. But no winter highway travel so far this year, just brief periods over 50 mph locally.

I use lower vents most of the time. Will use upper vents briefly between lower vent use. I found that since warm air rises, a brief period of upper vent use helps keep the warm air that is lower down, there a little longer.
 

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I find that once on the highway and once the car is heated up I put it on passive mode with the air set to front vents or front/feet only. If aimed towards the hands and head and traveling at 65mph with the heater set HI.. The air that comes out of the vents passively is extremely hot and more than warm enough for the driver in temps as low as 15degrees f.
 

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I should clarify that my comments relate to manual operation... but even if/when I run Auto, I tend to press A/C off and manage it myself.

Maybe I'm not giving Honda enough credit (and haven't looked up the parts to cross-check), but I don't think there's a humidity sensor. Or maybe it's combined with the one below the power button? My guess is that when in Auto, the system uses temperature as a proxy to determine what's 'comfortable' and manages the A/C that way (?).
It is combined. Almost all climate control systems that are automated in modern cars have one built in. They are cheap and useful.. If you look at the first sensor listed - you will find that it is the sunlight sensor..

 

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One thing worth mentioning in relation to poor hvac performance: ECO mode will reduce hvac to optimise fuel economy so if you were in ECO mode the system will have been reducing cabin heating to optimise mpg. This is a noticeable difference on cold days! The insight uses a traditional heater core (full of engine coolant) to heat the cabin and if the coolant in the heater core is not hot enough it will run the engine to keep it up to temperature. This affects the mpg more than any other accessory in the car. It will even disable EV mode to heat the cabin and prompts a message like "EV mode not available, cabin is being heated". ECO mode also reduces ac performance as well but since the Insight's compressor is not belt driven it doesn't have to run the motor to maintain temperature (although the electric compressor will use the battery and make the engine kick on a bit more).
 

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One thing worth mentioning in relation to poor hvac performance: ECO mode will reduce hvac to optimise fuel economy so if you were in ECO mode the system will have been reducing cabin heating to optimise mpg. This is a noticeable difference on cold days! The insight uses a traditional heater core (full of engine coolant) to heat the cabin and if the coolant in the heater core is not hot enough it will run the engine to keep it up to temperature. This affects the mpg more than any other accessory in the car. It will even disable EV mode to heat the cabin and prompts a message like "EV mode not available, cabin is being heated". ECO mode also reduces ac performance as well but since the Insight's compressor is not belt driven it doesn't have to run the motor to maintain temperature (although the electric compressor will use the battery and make the engine kick on a bit more).
That's why I only use manual heater operation. With just a little timely button pushing I get warmth AND top mpg !!
 
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