Windshield fogging up in cold weather

[ctuan13]

So long story short I'm having an issue I've never had before in my two years of ownership. I pulled out of my heated garage and left my house and like always had my temp set to around 73, vents set to face and floor and the AC switch set to on. I just had a few local errands to run, but after driving about 10 minutes I noticed it felt more humid inside the cabin and I smelled the characteristic smell you get when the compressor cycles off and the condensation on the evaporator begins to evaporate. Within minutes, every window was fogged up so badly I had to pull over because I was driving blind.

I tried every conceivable setting, but the compressor didn't seem to kick on and the fog wouldn't dissipate. Finally I opened the windows to try and eliminate some of the humidity. That combined with max defrost did seem to make some impact, but the entire rest of the drive, there was at least some condensation on the windshield. For reference the Heated garage is ~60°F and outside temp was ~27°F.

When I got home I pulled out my XTool bidirectional scanner and immediately did a full system scan. Other than the expected minor codes for the TCU being disconnected, there were none. I even scanned the ACCM (Air Conditioning Control Module) specifically and all seemed normal, with no faults. When I set the system to Max AC the life data showed the compressor kick on, pull an appropriate amount of amps and soon after the vent Temps began to drop. And yet if I set the system to 73 with the AC switch on, even running for an hour, the compressor didn't kick on once even to periodically dehumidify the cabin. Same with max defrost.

I've never had this happen before and I'm not sure if this is just some sort of Lightning climate control peculiarity or a serious issue. But without any codes and it being difficult to reproduce without the right conditions, I have my doubts that a dealership visit will accomplish much. Any thoughts, experiences or advice?

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[Pioneer74]

You didn't have it set to recirculate, did you? That will cause the fogging.

 

[ctuan13]

You didn't have it set to recirculate, did you? That will cause the fogging.

No, reciriculate was off and I almost never have it on. I also periodically check because I know sometimes the HVAC system will automatically turn it on.

 

[TaxmanHog]

Next time leave the AC button alone, the truck will do it's own command cycling when it's needed.

Also direct the air flow manually to Windshield & feet to get that warmed air to the glass surfaces quicker, you also can tap the max/defrost hard button for as long as needed to clear the windows.

 

[CavRider]

I had a similar experience this past Saturday early evening. Two people in the truck and cabin set to 70F on auto. After about three miles of driving it started to fog up and I looked down to see that AC was not on. Turned it on and the situation corrected within a few miles. Truck came out of a 65F heated garage at 31% humidity into around 7F ambient outdoor.

I've had lots of cars. There is not one I can remember for which I did not have to have the AC compressor ON for winter driving. If this truck turns that off without my permission I will be unhappy.

 

[RickLightning]

Speculating that heated garage is throwing off sensors.

 

[CavRider]

Speculating that heated garage is throwing off sensors.

... thus causing the climate to turn off the AC? Maybe. But the 2013 F150 I traded for this Lightning has been in that same garage for the last five years and that never happened that I can recall. Also, we have three other cars (two late model Fords) in another 45F garage and it does not happen to them.

So, confounding.

 

[Henry Ford]

Speculating that heated garage is throwing off sensors.

I agree with @RickLightning. I'll add that Max Defrost is the best way to clear the windows. It's one button push to turn on, one button push to turn off, and what Ford engineers think is the best configuration to defrost Windows. I trust they've spent more time thinking about it than I have.

 

[Wattsgas]

Wonder if the drain plug to the cabin evaporator is plugged....I had that happen on my ICE.

 

[Maquis]

I haven’t really paid much attention with the Lightning, but my Mach-E will run the AC compressor as needed without lighting up the button when in Auto mode or when air is directed to the windshield. Just because the light’s off, doesn’t mean it’s not running.

 

[WilliamRobert]

Is the cabin filter clean and the original type?

 

[TMND]

Reminds me of something that happened with my 99 7.3 power stroke. I was at a wedding in Kansas City in July and after leaving the wedding reception after midnight it was still in the mid 70s but so humid you felt like you were swimming in it. I also had offered to give rides home as I was a sober driver so the cab was beyond max capacity. The windows fogged up so bad I couldn’t even leave the parking lot without running the AC for 10 minutes full blast on the windshield. And while driving, rolling the windows all the way down wasn’t the solution. There was a happy medium of having them all cracked, blasting the AC and using a T-shirt to dry the windshield lol

 

[Mach Turtle]

Meanwhile, our Mach-E and Lightning usually turn on the AC automatically when we don't want or need it in our temperate and mostly dry climate. Guess this is what happens when the designers make a system that tries to perform in a really wide range of conditions.

Maybe someday they'll have HVAC maps based on the seasons in different climate zones. Hopefully a better Guess-O-Meter which uses current and forecast weather and elevation changes on planned routes will come first, though.

 

[CavRider]

I haven’t really paid much attention with the Lightning, but my Mach-E will run the AC compressor as needed without lighting up the button when in Auto mode or when air is directed to the windshield. Just because the light’s off, doesn’t mean it’s not running.

In my case it is abundantly clear that it was not running and that turning it on manually was the "fix" that was required. What I don't quite understand is how it was ever turned off. At this point I am going to assume that I must have been dickin around with the screen and somehow turned it off myself.

Yeah, that's it, it's my fault unless and until it repeats.

 

[TaxmanHog]

The HVAC's systems in my present and prior three F series have always been schizophrenic.

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