I'm not sure what brought up this thought, however it's been on my mind and I'm curious as to whether any member of this forum can shed some light on the subject. After buying my 2nd Grand Cherokee, I noticed that the automatic A/C control panel had what looked like a sunlight sensor built into it. I've seen this sensor in other Mopar vehicles, but never thought much of it. I've owned my share of vehicles equipped with one form of auto A/C or another, yet my GC seems to do MUCH better at maintaining not only the cabin temperature as a whole, but also managing zone temps when the significant other and I have our temps set differently.
After some digging, it turns out said sensor isn't a solar sensor at all, it's a dual infrared sensor designed to detect the heat radiation of the front seat passengers, plus the surrounding areas. All the systems I knew of previously consisted of a small fan mounted in front of a thermistor which took a sample of cabin air temperature and used that to calculate the proper adjustments (sometimes in conjunction with other sensors).
Maybe I'm missing something, but is the infrared system not leaps and bounds better than the ambient system? Say in a particular car, the thermistor is mounted slightly below a dash vent. Would it not just sample a disproportionate amount of cold air that's naturally sinking, vs. actually knowing what temperature the majority of the cabin and/or the passengers display? Granted, maintaining the temperature of an automotive cabin is basically impossible without massive investment in thermal glass and insane amounts of insulation, however while they're in motion the modern systems are actually quite capable of providing a comfortable environment.
Case study: I've made the ~2.5 hour journey to a buddie's cabin several times already this summer, in temps varying from 75-98 degrees. In my Volt, setting the climate to "comfort" mode, selecting 70 degrees, and leaving all other settings on AUTO results in a both A: too much fan speed and B: far too cold of an output temperature to be tolerable for that length of drive. I constantly find myself adjusting either the temp or fan speed trying to find the right combination. Automatic just doesn't work. Looking at the schematics, the Volt system doesn't use an interior temperature sensor at all, it seems to rely on a combination of sun load sensor inputs and a "windshield temperature sensor/in-car humidity sensor" mounted to the front glass.
In contrast, my Jeep has absolutely no problem keeping the cabin at the perfect temperature, all settings being the same. 70 degrees in both zones, auto fan and auto mode selection. I can literally watch the display change when it goes from vent to bi-lev, recirc to fresh, and back again while it does it's job maintaining the selected temperature. I can't help but think this is directly related to the system being used. The Jeep uses no sun load sensor, no cabin temp sensor, no humidity sensor. It simply relies on radiant heat readings from the object it's sensors are focused on. In this case, that's me. By forming a picture of my body's PERCEIVED temperature of the cabin, instead of the temperature of the cabin itself, it has a marked advantage in maintaining a truly comfortable environment.
Since I've noticed this phenomenon, I've played with several auto A/C units in various vehicles at work while test driving, and I have to say none of them seem to work as well as the system in my Jeep. I also have a 2013 Chrysler 200 that a buddy and I bought for a flip, and it uses the IR sensor technique in it's system and again, it's quite good.
Anyone else care to chime in with their experiences?
After some digging, it turns out said sensor isn't a solar sensor at all, it's a dual infrared sensor designed to detect the heat radiation of the front seat passengers, plus the surrounding areas. All the systems I knew of previously consisted of a small fan mounted in front of a thermistor which took a sample of cabin air temperature and used that to calculate the proper adjustments (sometimes in conjunction with other sensors).
Maybe I'm missing something, but is the infrared system not leaps and bounds better than the ambient system? Say in a particular car, the thermistor is mounted slightly below a dash vent. Would it not just sample a disproportionate amount of cold air that's naturally sinking, vs. actually knowing what temperature the majority of the cabin and/or the passengers display? Granted, maintaining the temperature of an automotive cabin is basically impossible without massive investment in thermal glass and insane amounts of insulation, however while they're in motion the modern systems are actually quite capable of providing a comfortable environment.
Case study: I've made the ~2.5 hour journey to a buddie's cabin several times already this summer, in temps varying from 75-98 degrees. In my Volt, setting the climate to "comfort" mode, selecting 70 degrees, and leaving all other settings on AUTO results in a both A: too much fan speed and B: far too cold of an output temperature to be tolerable for that length of drive. I constantly find myself adjusting either the temp or fan speed trying to find the right combination. Automatic just doesn't work. Looking at the schematics, the Volt system doesn't use an interior temperature sensor at all, it seems to rely on a combination of sun load sensor inputs and a "windshield temperature sensor/in-car humidity sensor" mounted to the front glass.
In contrast, my Jeep has absolutely no problem keeping the cabin at the perfect temperature, all settings being the same. 70 degrees in both zones, auto fan and auto mode selection. I can literally watch the display change when it goes from vent to bi-lev, recirc to fresh, and back again while it does it's job maintaining the selected temperature. I can't help but think this is directly related to the system being used. The Jeep uses no sun load sensor, no cabin temp sensor, no humidity sensor. It simply relies on radiant heat readings from the object it's sensors are focused on. In this case, that's me. By forming a picture of my body's PERCEIVED temperature of the cabin, instead of the temperature of the cabin itself, it has a marked advantage in maintaining a truly comfortable environment.
Since I've noticed this phenomenon, I've played with several auto A/C units in various vehicles at work while test driving, and I have to say none of them seem to work as well as the system in my Jeep. I also have a 2013 Chrysler 200 that a buddy and I bought for a flip, and it uses the IR sensor technique in it's system and again, it's quite good.
Anyone else care to chime in with their experiences?