Heat comes on while in AC mode

[steve68]

Yup,
supposed to do that, whatever, bad design!

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[GrubbyBaja]

Also, is it my imagination, or does it sometimes come on by itself, when I have it turned off?

I see you have the 6-speed. The HVAC system is not coming on by itself, it is coming on when you shift into 3rd or 5th and your knuckle/finger hits the auto button or hits the fan bezel...I do it all the time. Some people have also accidentally hit the hazards button while shifting.

 

[A 2]

Here’s my 2cents. I believe two things are happening here. First, in a new car the programming is learning. My JT used to do this also but eventually after several weeks of use, does it every once in a while. Second, my guess is there is a humidity sensing thing happening. The heat, similar to a reheat feature in a building, blasts some hot air to get the humidity out.

That’s my guess and I’m sticking to it.

 

[MrZappo]

Here’s my 2cents. I believe two things are happening here. First, in a new car the programming is learning. My JT used to do this also but eventually after several weeks of use, does it every once in a while. Second, my guess is there is a humidity sensing thing happening. The heat, similar to a reheat feature in a building, blasts some hot air to get the humidity out.

That’s my guess and I’m sticking to it.

That isnt the way humidity works ... Hot air does not "get the humidity out" ... Changing the temperature of air does not change the amount of water in it ... Humidity is relative to the temp but the amount of water in the air does not change ...

Letting hot air in on a humid day would raise the humidity level substantially in the cabin which has had the humidity reduced by the air conditioning process.

AC systems typically do not learn like you are saying ... The transmission does and adapts to your driving style ... A/C systems have fixed programming and some advanced ones have PID loops that adapt to changing inputs but they do not "learn" ....

 

[Han Amj]

As far as I remember it has to do with the CO2 levels in the cabin. So yes it’s by design. I read this in a bulletin from FCA last year.

 

[DreamedofaJeepSomeday]

I see you have the 6-speed. The HVAC system is not coming on by itself, it is coming on when you shift into 3rd or 5th and your knuckle/finger hits the auto button or hits the fan bezel...I do it all the time. Some people have also accidentally hit the hazards button while shifting.

I had noticed that I had accidentally touched the knob a few times and turned it on. Maybe that explains all of the turn-on events.

 

[DreamedofaJeepSomeday]

Changing the temperature of air does not change the amount of water in it ... Humidity is relative to the temp but the amount of water in the air does not change ...

Not to be argumentative, but this seems contradictory to me. Cooling the air causes moisture to condence on the coils and drain outside the vehicle; that does indeed change the amount in the air.

 

[MrZappo]

Not to be argumentative, but this seems contradictory to me. Cooling the air causes moisture to condence on the coils and drain outside the vehicle; that does indeed change the amount in the air.

The cooling process that you have said does indeed remove water from the air inside the cabin via condensation of the water onto the condensing coil ... Yep ...

What I was saying is that if the system opens vents to let outside air into the (already cooled and dehumidified cabin), and lets HOT air into the cabin, that will not lower the humidity (just because the air is hot) ... It will simply add humidity back into the cabin that the A/C system will have to remove again ...

People generally think that hotter air is drier than cooler air just by virtue of its temperature ... That is not true at all ... This is what I was trying to get across ...

 

[DreamedofaJeepSomeday]

The cooling process that you have said does indeed remove water from the air inside the cabin via condensation of the water onto the condensing coil ... Yep ...

What I was saying is that if the system opens vents to let outside air into the (already cooled and dehumidified cabin), and lets HOT air into the cabin, that will not lower the humidity (just because the air is hot) ... It will simply add humidity back into the cabin that the A/C system will have to remove again ...

People generally think that hotter air is drier than cooler air just by virtue of its temperature ... That is not true at all ... This is what I was trying to get across ...

Agreed.

In older cars, hot air coming from the defrost vents removed condensation from inside the windshield because hot air can hold more water that cold air. But the moisture still stayed inside. Modern cars use colder air from the coils for this purpose because it is dehumidified air.

 

[steve68]

As far as I remember it has to do with the CO2 levels in the cabin. So yes it’s by design. I read this in a bulletin from FCA last year.

Produce the bulletin or bulletin number, simple as that...........

 

[Punknhead]

Had an issue with mine where defrost was coming on by itself and blowing hot. I could not control it. They replaced the control system—whatever that is. All good now.

 

[DreamedofaJeepSomeday]

I have noticed if the outside temperature is only a few degrees higher than the temperature setting, it blows warm air until i lower the set temperature somewhat. Don't know if this is defect or just the way it works.

 

[Jt-wrx]

I just took delivery (pictures coming) of a 2020 Gladiator Overland. First trip was from Stuart, FL to Jacksonville. 237 miles one way and about 3.5 hours. Did round trip in 1.5 days. While running up and down i-95 (outside temp 89 F) Air running on Auto or NOT on Auto, set at 70 for inside, Heat started coming out from under the dash.

Both sides of the cockpit floor. So it was cold air coming out of the Dash Air vents and heat coming out from under the dash some place. Would last about 10 min than stop and would be well for another hour or so, and than it did the same thing. Trying to explain or trouble shoot this with a Tec at Jeep, will be very hard to duplicate at the dealers.

Any thoughts or suggestions on what to do?

Bob

you have to plug the drain holes in the floor, mine did same thing, plugged those dang holes and good to go, the jeep rubber floor mats come with nice little rubber pop in plugs, easy peasy

it was unreal on hot days how hot air from under the jeep from exhaust/engine/road etc. would just blast up through those holes boiling your legs

 

[TheSolarWizard]

My understanding is that the AC system is supposed to introduce fresh air into the cabin periodically and that it does this because and exhaust leak or exhaust in general can inadvertently be drawn into the cabin via a potentially open soft top window, incorrectly fitted or otherwise poor seal condition (drain plugs missing is my first thought). Supposedly it’s disabled or supposed to be when the AC isn’t on recirculate

on my F150 I’ve noticed that when the engine is still running rich upon cold start if I have the back window open I can definitely smell it

 

[ShadowsPapa]

My Overland also does this. The system periodically opens the outside air flap for a couple minutes. It appears to be programmed into the system. It is probably to keep the air from getting stale, and to keep the coil from freezing up.

I run it in manual AC/Recirc mode year round. I keep it at 67° when I want cold air from the vents during warm weather, and adjust the temp a few degrees up or down to get the amount of heat I want when it's cold. I don't send air to the floor, and rarely need the defroster here.

That was pointed out as a normal thing in a message a couple of weeks or so ago - how every xx minutes it would do that by design. But seems some won't accept that explanation either.
Just because OTHER vehicles don't do this doesn't mean it's not part of the JT's HVAC. Doesn't matter how many other vehicles you've driven or owned that did not do this. It simply means they handle things differently - not that they are correct or right, or wrong. Just different.
I tried to ask people to track the timing but so far, no one but the person who posted the explanation they found that said something like 40 minutes, I believe. And it was indeed to introduce fresh air.
Everyone is an engineer and knows better than the Jeep engineers, of course. If they don't like it, then it's wrong, period.

I leave mine in auto mode and set to about 69 in the summer, about 69 or sometimes 70 in the winter.
My wife is the only one who ever changes it and she doesn't understand auto mode - so doesn't like it (sounds familiar)

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