2019 HVAC Issue - JeepForum.com
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post #1 of 23 Old 10-22-2019, 01:20 PM Thread Starter
csacsa
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2019 HVAC Issue

Outsude temperature below 60 degrees. If I set the temperature anywhere around 70 degrees, for the first 10 miles it is actually at 80 degrees. It then starts to slowly come down to the correct temperature at 20 miles. Dealer said this normal. Never had any other Jeep or any other car for that matter do this. Is this correct?

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post #2 of 23 Old 10-22-2019, 01:30 PM
Jurassic_Jeep
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Its not so much miles driven, its more how long it takes to bring the entire cabin at the the temperature you want. For example, when you set it to 70 degrees, it determines that air going in is 60 degrees, so if it blows 70 degrees air temperature in, it will take twice as long to warm up the cabin if it were to blow 80 degree air in. This is what typically the auto function does.

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post #3 of 23 Old 10-22-2019, 01:36 PM Thread Starter
csacsa
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When you say the "auto" function. I have that turned off. If we are talking about the same thing.
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post #4 of 23 Old 10-22-2019, 01:43 PM
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I believe its the same if auto is on or off, i.e. it will blast hotter or cooler air (at first) to get the cabin temps to the set point temperature by measuring the intake air temperature.

By the way, my jeep does the same as yours.

2014 Jeep Grand Cherokee Summit 4x4 3.6L V6.
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post #5 of 23 Old 10-22-2019, 01:46 PM Thread Starter
csacsa
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Well I certainly appreciate the input. I don't like the engineering idea behind this, but at least my mind has been put to ease. Thank you.
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post #6 of 23 Old 10-22-2019, 01:49 PM
Jurassic_Jeep
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by the way, are you measuring the air coming out of the vent with a thermometer or something? if so, try putting it somewhere else, like in the middle of the cabin, or near your feet. I forgot where the intakes are, but remember it being lower level.

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post #7 of 23 Old 10-22-2019, 01:54 PM Thread Starter
csacsa
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Yep, thermometer at the vent
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post #8 of 23 Old 10-22-2019, 02:06 PM
Jurassic_Jeep
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then this makes total sense. It might be annoying (temporarily), but if it worked any other way, it would take a lot longer for your cabin to warm up or cool down when there is a large temperature differential between set and actual (and ambient to a lesser extent).

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post #9 of 23 Old 10-22-2019, 04:17 PM
Fast55
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It's what's called "supply air temperature reset". The farther from set point the cabin is, the hotter the discharge air will be. It will slowly come down as the cabin temperature gets closer to set point. All normal.

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post #10 of 23 Old 10-22-2019, 04:22 PM Thread Starter
csacsa
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I understand but I have had over 20 vehicles in 40 years of driving. The latest before this 2019 was my 2013 Grand Cherokee. None of them did this.
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post #11 of 23 Old 10-22-2019, 08:57 PM
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Try sticking that thermometer in a vent in your house. I bet it reads a lot higher than what you have your thermostat set at.
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post #12 of 23 Old 10-22-2019, 09:53 PM
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Quote:
Originally Posted by csacsa View Post
Outsude temperature below 60 degrees. If I set the temperature anywhere around 70 degrees, for the first 10 miles it is actually at 80 degrees. It then starts to slowly come down to the correct temperature at 20 miles. Dealer said this normal. Never had any other Jeep or any other car for that matter do this. Is this correct?
You definitely found a flaw, we discussed this in another thread.

https://www.jeepforum.com/forum/f309...ystem-4338947/

It is not correct to how it should operate, I feel it is a firmware programming issue. Like you my JGC operates differently than 30 years of car ownership. All this comparison to home systems, intake temp vs vent, discharge temp, just doesn't correlate to a car system. First of all, vehicles typically default to pulling fresh air, you have to hit the recirculate (internal intake) or MAX AC to switch off fresh air.

Plus, unlike a home system a vehicle has both hot and cool temperature sources available at the same time. In old school conventional vehicle system in manual mode, when you roll the manual dial over to the red/hot it simply opens the flow of hot engine water into the heater core. If you are running your AC it warms the air by whatever amount you roll the dial. You can set it by feel whatever is comfortable for a discharge temp. When you do this it will blow a stable continuous blended hot/cool air.

For some reason the JGC doesn't allow you to set a warm/cool blend that is of your making when in Manual mode. As you notice after a while it will settle, but it seems to over react to temp changes or initial start. I call it a quasi-manual, this because it seems to Auto adjusts your temp at extremes but doesn't mess with the fan. When in full Auto mode it does it all, fan and temp.

Love my JGC, I chalked this up a long time ago as a system quirk, not that big of a deal. If I want a blended temp I just put it on Auto.

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post #13 of 23 Old 10-22-2019, 10:24 PM
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No offense, but this is not a flaw. You say you notice that after a while, it will "settle". That's because the sensor and mass of plastic around it have time to equalize the temperature and sensor value, with the actual cabin temperature. A modern HVAC system in any vehicle can substantially change the actual temperature that you feel much faster than any type of sensor can react. Manufacturers use software to "anticipate" this to varying degrees of success.

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post #14 of 23 Old 10-23-2019, 05:59 AM
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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.

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post #15 of 23 Old 10-23-2019, 07:56 AM
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Those of you that read the owners manual know that these late model WK2s don't have manual temperature control. The system only allows for manual override of blower speed, air distribution mode, A/C status and recirculation control. 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. The temperature is target cabin temperature. The vent output temperature can vary quite a bit from the setting, if it needs to quickly warm or cool the cabin.

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