HVAC System and Fogging Windows

[Dasoss]

I believe OP knows this, and is seeing the opposite behaviour...

Sorry I misread his post. That is odd. My guess is that the inside hear exchanger retains condensate from when it was cooling the evening before. Perhaps the drain ts clogged. When it changes to heat it evaporated rhe water, which then condensed on the cooler windscreen. If so it should clear after e whe.

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[ndmiller]

Feel like it switched behavior in the last update. Fresh air isn''t having humidity removed anymore, but 3 weeks ago it was. Same temps 65-80, so morning commute fog free with fresh air became the entire T fogging up during morning commute this morning. Turned on recirc and it cleared right up.

Tried again turning AC down to a degree or below to what it though the outside temp was and seemed like AC compressor wasn't coming on with Fresh air....so weird.

 

[mczouav]

I've had my R1T since 2022 with no real issues with Interior fogging issues. At least not to a level that concerned me.

But, lately I've noticed the front window fogging in this early fall weather. I'm using an Auto Setting with a temp setting of 70, recirculation off, and a fan speed of low or med. The fogging is independent of the drive length as it happens on short drives and really long drives.

What's really strange is the fogging disappears if I turn on recirculation which seems backwards. The other thing that happens if I turn on recirculation is the interior gets colder.

Another oddity is that if I push the defogging button it gets uncomfortably warm regardless of the temperature setting I have it set to.

My question is whether other people have observed this or if there is something strange going on with my R1T specifically.

I don't recall any issues with previous firmware version. I'm on firmware version 2025.34.01

is the area under floor mat under the accelerator pedal wet?
if so it fits +/- the symptoms I had.
I had drain plug clogged in gen1 ac box. It accumulated water, overflowed inside the car and corroded the ac coils. Ac was anemic and heat on made fog. If so might Need servicing and new gen 2 HVAC box.
Just an idea…
MC

 

[Dasoss]

is the area under floor mat under the accelerator pedal wet?
if so it fits +/- the symptoms I had.
I had drain plug clogged in gen1 ac box. It accumulated water, overflowed inside the car and corroded the ac coils. Ac was anemic and heat on made fog. If so might Need servicing and new gen 2 HVAC box.
Just an idea…
MC

Gen 1 uses a resistance heater. I'm guessing it heats the liquid in the thermal management system, rather than heating the air directly. Gen 2 has a heat pump. I'm guessing that the heat punp has its heat exchanger in the thermal management loop. I wouldn't think that the A/C box is very different between gen 1 and gev 2.

 

[mczouav]

Gen 1 uses a resistance heater. I'm guessing it heats the liquid in the thermal management system, rather than heating the air directly. Gen 2 has a heat pump. I'm guessing that the heat punp has its heat exchanger in the thermal management loop. I wouldn't think that the A/C box is very different between gen 1 and gev 2.

the gen1 hvac box has a water plug issue well known of Rivian. they redesigned it for gen2...

 

[Dasoss]

the gen1 hvac box has a water plug issue well known of Rivian. they redesigned it for gen2...

I'm glad about that. I have a 2026 r1s quad launch edition.

 

[s4wrxttcs]

is the area under floor mat under the accelerator pedal wet?
if so it fits +/- the symptoms I had.
I had drain plug clogged in gen1 ac box. It accumulated water, overflowed inside the car and corroded the ac coils. Ac was anemic and heat on made fog. If so might Need servicing and new gen 2 HVAC box.
Just an idea…
MC

Thanks for this info. I'll check it.

Something is definitely different than it was.

 

[cbrcanuck]

Thanks for this info. I'll check it.

Something is definitely different than it was.

Let us know if you find anything - I’ll be watching this thread…

 

[Flyinryan]

I'm having the same issue. Windows completely fogged over this morning. I couldn't see a thing. Had to pull over put defog on high and still took a very long time to defog. I was sweating by the time I could see out.

 

[rodhx]

This has been my one real complaint with our Rivians. The defroster logic has been screwed up since winter 2023 when there was a rash of frozen ac components in northern climates. I never experienced the fogging problem prior to that but the secret software "fix" made the system downright dangerous here in humid south. The AC compressor doesn't engage enough to dehumidify the interior, unlike every other defroster setting since the dawn of the automotive age . The best workaround I have found is to dramatically lower the temp to force the AC on and be sure to have the windshield vent selected. But I never had to do that prior to winter 2023. When I was at the SC back then with this as one of my issues the manager told me about the software change that had been pushed.

 

[s4wrxttcs]

Let us know if you find anything - I’ll be watching this thread…

I didn't feel any moisture under the mat.

The update didn't really fix the behavior, but it now has a mixed mode which gives mixed results as expected.

I'm going to get my vehicle serviced soon for this issue. I was hoping the update would fix it but it definitely did not.

I live in a very wet and cool/moderate climate.

 

[Phatman113]

I didn't feel any moisture under the mat.

The update didn't really fix the behavior, but it now has a mixed mode which gives mixed results as expected.

I'm going to get my vehicle serviced soon for this issue. I was hoping the update would fix it but it definitely did not.

I live in a very wet and cool/moderate climate.

Did you ever get a chance to just blast the heat for a few hours and see if you can dry out the interior? Does that give you a break from the issue for a little while?

 

[cbrcanuck]

I didn't feel any moisture under the mat.

The update didn't really fix the behavior, but it now has a mixed mode which gives mixed results as expected.

I'm going to get my vehicle serviced soon for this issue. I was hoping the update would fix it but it definitely did not.

I live in a very wet and cool/moderate climate.

Mine is still behaving the same. I’m also in wet climate and it’s definitely from odd behaviour in the climate control, I don’t have any excess moisture in the cabin. I haven’t done a software update in a bit because of all the bug reports lately but hoping this gets resolved before winter really sets in!

 

[s4wrxttcs]

Did you ever get a chance to just blast the heat for a few hours and see if you can dry out the interior? Does that give you a break from the issue for a little while?

My break is to simply use the wrong mode as 99% of the time I don't have a fogging issue in that mode.

To clarify - The issue I'm having is the front windows are fogging when the icon is showing air coming in from outside the vehicle. Then when I switch it to recirculation the fogging goes away.

I did go on two 3+ hour drives recently that didn't seem to alleviate the fogging when air recirculation was off.

 

[s4wrxttcs]

I'm having the same issue. Windows completely fogged over this morning. I couldn't see a thing. Had to pull over put defog on high and still took a very long time to defog. I was sweating by the time I could see out.

They should change the symbol to a death symbol instead of the blue outline thing.

I'd die of heat stroke if I had to put it into defog mode for a long period of time.

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