2019 HVAC Issue - Page 2 - JeepForum.com
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post #16 of 23 Old 10-23-2019, 08:21 AM Thread Starter
csacsa
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Would this explain why the a.c. turns on by itself in the summer? The a.c. light doesn't come on but the air coming out of the vent is ice cold. When I pulled the fuse for the a.c., the vent air acted "normal"

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post #17 of 23 Old 10-23-2019, 08:36 AM
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Originally Posted by tampamark View Post
We will have to agree to disagree. What you are referring to when you say the "sensor and plastic around it equalize" is the HVAC system using intelligence to apply the temperature to the system. In other words, it is trying to Auto adjust the temp setting.

In every car I have owned and as the OP says, in TRUE manual mode there should be NO intelligence or sensor involved. You would simply blend the heater air and cool air to what is comfortable and move on.

In every car I have ever had the temp inside or outside could be 90 degrees, if I set the output temp at a certain level manually it blows just that temp regardless of environmental conditions. I can't do that in my JGC, I set what I want as an output temp manually and you are correct, it uses the sensor to determine the difference between what I request and what is the current cabin temp and it decides to alter the temp I selected and blow a much more aggressive temp from the vents.

Tell me how the automatic sensor interacting and controlling the HVAC system is Manual control of your system! It should be completely disabled with no adjustment to temp or fan when in manual mode.
There is no true "manual" control setting so like it or not, this is not a flaw. What I'm referring to is the thermal mass of the sensor and its housing. The air temperature you feel is obviously changing much faster than the sensor and the plastic around it can change. The only way the HVAC system could react the way we would all like it to, would be to have a bare bead thermistor or RTD hanging in the cabin around your body position. That's never going to happen for obvious reasons. What you think it should do and how it actually operates are two different things but that does not mean there is a flaw, just how it was designed. This isn't a 1980's vintage CJ.

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post #18 of 23 Old 10-23-2019, 08:50 AM
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Originally Posted by csacsa View Post
Would this explain why the a.c. turns on by itself in the summer? The a.c. light doesn't come on but the air coming out of the vent is ice cold. When I pulled the fuse for the a.c., the vent air acted "normal"
This is another automatic feature. When the system senses high humidity, it will bring in the A/C compressor to dehumidify the air and prevent window fogging. My 2013 Genesis does this as well.

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post #19 of 23 Old 10-23-2019, 10:25 AM
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if you wanted another analogy, your standard stove top with a heating element. Despite the knob being set to low, medium or high...there is actually only 1 temperature, and its either on or off. When you first want to boil water, that stove top is super red with temperature close to 500 oC or so for several minutes, then it turns off, then on a bit more, then off a bit, On and off....and its the computer along with the feedback sensor that determines the overall temperature. It just basically balances the on and off to keep the temperature, but when its on, the temperature is always 500oC at the heating element, but your water is at the temperature you want.

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post #20 of 23 Old 10-23-2019, 03:02 PM
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That's digital or on/off control. The oven or your home A/C is a better example. The element or burner is on until you reach set point and then turns off. Same for the home A/C. It runs and makes very cold air until the thermostat turns it off. Some people like my wife will insist that the oven gets to 350 degrees faster if she sets it to 500.

Umm, no.

Just as setting your thermostat to 65 will not cool your house down to 72 any faster than just putting it at 72. The GC's are different. The A/C compressor runs "on" at full cool and the blend doors select how much of a mix between that and the hot air from the heater core to make discharge air set point. That's modulating or analog control. That set point changes and becomes closer to the set temperature on the dash the closer you get to it and vice versa. The A/C compressor can cycle off completely when you're at or below set point, but it's the blend doors modulating between the hot and cold air available that determines the discharge temperature.

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post #21 of 23 Old 10-23-2019, 06:01 PM
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Originally Posted by ColdCase View Post
Although these features can be controlled manually, temperature control will continue to operate automatically. As noted, temperature control is aggressive to quickly adjust cabin air temperature.
You are correct that it states in the Owners Manual that the HVAC Manual override controls those elements, but it doesn't say that temp stays in auto mode. Perhaps by ommission they imply it, certainly the statement from the manual makes no mention of temperature change either way. I figured it is because it is so basic a premise, modulate temp manually, that it didn't need mentioning. But neither is change blower speed and they bring that up.

I agree that they designed it so that you NEVER can fine tune a temp that is stable and continuous manually. Hence I say it is a flaw, that is the dumbest thing ever, when I am in manual mode and find it is a little colder and change it up a couple degrees and it blows 90 degree air out is just dumb programming. So if they designed it that way it was a flaw in their thinking.

I have owned many modern cars this is the only one that operates like this in manual operation.

I love this JGC, everything about it is fantastic and I have been very pleased. Most modern high end cars that I have owned have had some poor feature or completely missing that I felt is basic to car ownership. This one is minor, it is what it is.

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post #22 of 23 Old 10-23-2019, 07:00 PM
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My bad, it seems that much the following words were removed from the newer model OMs, dunno the implications of that:

"Manual Operation Override

The system allows for manual selection of blower speed, air distribution mode, A/C status and recirculation control.

The blower fan speed can be set to any fixed speed by adjusting the blower control. The fan will now operate at a fixed speed until additional speeds are selected. This allows the front occupants to control the volume of air circulated in the vehicle and cancel the Auto mode.

The operator can also select the direction of the airflow by selecting one of the available mode settings. A/C operation and Recirculation control can also be manually selected in Manual operation.

Although these features can be controlled manually, temperature control will continue to operate automatically."

The way its designed is more in line with European (German) luxury car philosophy, where they trust the system to control cabin temperature without making the driver think about it. All my Mercedes and BMWs with auto temp control of decades ago worked like that. Not a flaw, but a difference in HVAC design approach. You may disagree with the design philosophy, one that suits 99% of drivers well.

When its a little cool or warm for me, its routine to bump the temp settings a little. Just don't bump it more than a couple degrees at a time. My 2011 has an IR occupancy sensor, however, that helps the HVAC to make smarter decisions than the newest models I hear.

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post #23 of 23 Old 10-23-2019, 07:36 PM
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It is all good!

Before my Wife's BMW that we bought in 2009 I had never had a car with an Auto option for temperature control. That car is gone and she has a Jaguar now which she never uses Auto. This since the majority of the time it is MAX AC anyway in our Florida heat.

Both operated in true manual mode as I described. We just went out in her car earlier and I increased the temp a couple degrees as it blows cold as hell even at lowest fan setting and the sun was down. It was a pleasure to have it warm the vent air ever so slightly without blasting me with uncomfortably hot air like my JGC. Even changing it by 5 degrees didn't create an over-reaction.

You are right, the Auto mode suffices for 99% of owners. Like I have said, it is a minor gripe. This is getting beat in the ground now, only reason I am still arguing the point is that I am told this is normal operation in modern cars and Euro cars, which is contrary to every car I own right now and have owned in the past. Not to mention I travel for work and rent 20 different cars each year. Never have seen one like the way the JGC operates (Kia/Nissan/Toyota/Cadillac/Hyundai/Ford/Chevy).

I feel this is opposite day from Seinfeld!

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