2017 Max Defrost button doesn't seem to do what I want it to do...

[kmarnes]

In the morning, when there is frost on my windows... I hit the Max Defrost button and it's basically ignored. I normally keep it on Auto climate.

Anyways, I can manually crank the fan and temperature and then set it back to auto when everything is good. So the HVAC is working fine... it just seems like the button doesn't do much.

This is the description from the manual and matches my expectations for pretty much every car out there:

MAX Defrost: Press to switch on defrost. The driver and passenger settings set to HI, air flows through the windshield vents, and the fan adjusts to the highest speed. You can also use this setting to defog and clear the windshield of a thin covering of ice. The heated rear window also turns on when you select maximum defrost. E Note: To prevent window fogging, you cannot select recirculated air when maximum defrost is on.​

Is there something I'm missing or have I encountered my first glitch?

 

[Odrapnew]

I have a '14 model, so I don't have the Max Defrost button, but I have a few questions.

Is the engine warm?
Could it be that the climate control is keeping the fan low until the engine is warm?
The explanation makes it sound like the climate temp is set to Hi, so it may be limiting the fan speed until the engine warms up.

I ask because I know my '14 climate control, when set to Auto and temperature set to Hi, will keep fan speed low until the engine gets warm.
Once the engine warms up, the fan speeds up as well. Again, I don't have Max Defrost button, all my results are with it set to Auto.

 

[peterk9]

Just gave mine a try. It has been sitting in the garage for a couple days. After starting the vehicle I noticed that the Climate light at the bottom is ON and the system is on AUTO. I pressed the Max Defrost button, the AUTO light went OFF and the blower motor picked up somewhat in speed. I could then feel the cold air blowing on me from the defroster vents. It seems to me that I used the Max Defrost once before after driving a minute or two to defog the windows and the blower motor was running much, much faster. Perhaps it waits for the engine to warm up a little before going 'full blast'.
EDIT: Looks like Odrapnew posted after I started mine and went to the garage.

Peter

 

[kmarnes]

The only time I really need to max defrost the car is first thing in the morning when I'm leaving for work. I start the car, press max defrost, then scrape the windows. Then I get into the car and find my windshield is still heavily fogged up.

But paying closer attention, the act of switching from auto to max defrost seems to really only divert the airflow to the windshield, without cranking the heat or the fan speed. It does sound like the airflow increases a little bit, but I actually think it's just the same airflow going through smaller vents.

It doesn't really do a whole lot until I manually crank it... because I'm literally just waiting for it to clear up before I start driving. So I feel like it's not doing the right thing. And then once I'm done, I have to manually crank down the temperature which takes a few seconds, so it's slightly annoying.

 

[Chris-74]

Check that the temperature setting displays “hi” at the top of your Sync screen after pressing max defrost. Mine seems to work as it should, but I prefer using remote start on cold mornings anyway.

 

[kmarnes]

It does say hi at the top of the sync screen, but I still get the same behavior. It might be by design though. My assumption is that it should blast max temperature at max fan speed and it's definitely not doing that.

 

[peterk9]

It does say hi at the top of the sync screen, but I still get the same behavior. It might be by design though. My assumption is that it should blast max temperature at max fan speed and it's definitely not doing that.

Hard to blast max temperature when you just turned the engine on. As I previously mentioned, mine did 'blast' air once the engine warmed up a little. A lot more air than when I just started it up. I'm guessing it works somewhat along the lines of the heater. If left in AUTO it doesn't really start blowing much until the engine warms up.

Peter

 

[Odrapnew]

I think the way it’s working makes sense.
If you think about the purpose of the defrost, to defrost the windows, blowing below freezing air across the windshield wouldn’t defrost the window.
If the engine is just barely warm, blowing a lot of air across the heater core could cool it down enough to still blow sub-freezing air onto the windshield.
So, the fan speed is on low(or slightly above) until the engine(and heater core) are warm enough to be blowing warm air across the windshield at higher fan speeds.

 

[peterk9]

It does say hi at the top of the sync screen, but I still get the same behavior. It might be by design though. My assumption is that it should blast max temperature at max fan speed and it's definitely not doing that.

You could always try plugging the block heater into a timer set to come on a couple hours before you start the vehicle to see if it makes a difference.

Peter

 

[kmarnes]

Alright, so I paid extra special attention to everything this morning. It was 2C, so no frost, but everything was fogged up.

When I transition from auto to max defrost immediately after a cold start, it puts the temperature on high, but the fans are only on 6/7 speed. After about 3-4 minutes, it'll automatically go to full 7 speed. And if I press auto after that, everything goes back to normal. So if I need that extra little boost, I can just kick it up to the fastest speed. I find the programming is a little too conservative for my particular weather conditions.

I think the mistake I was making before was that I'd manually crank the temperature and the fan speed... but if you muck with the temperature, then it remembers.. and then when I go back to auto, I need to manually dial it back down. So "auto defrost + fan speed increase" is good enough for me. I don't think it's broken, it's just over-engineered.

The difference between fan speed 6 and 7 is like double. And 7 is the only speed that will quickly defrost my windshield, even when cold.

 

[peterk9]

Alright, so I paid extra special attention to everything this morning. It was 2C, so no frost, but everything was fogged up.

When I transition from auto to max defrost immediately after a cold start, it puts the temperature on high, but the fans are only on 6/7 speed. After about 3-4 minutes, it'll automatically go to full 7 speed. And if I press auto after that, everything goes back to normal. So if I need that extra little boost, I can just kick it up to the fastest speed. I find the programming is a little too conservative for my particular weather conditions.

I think the mistake I was making before was that I'd manually crank the temperature and the fan speed... but if you muck with the temperature, then it remembers.. and then when I go back to auto, I need to manually dial it back down. So "auto defrost + fan speed increase" is good enough for me. I don't think it's broken, it's just over-engineered.

The difference between fan speed 6 and 7 is like double. And 7 is the only speed that will quickly defrost my windshield, even when cold.

That's the way mine works as well if I leave everything alone and just hit Max Defrost. If I recall from my test, hitting Max Defrost again to turn it OFF will automatically turn AUTO back ON assuming it was on AUTO to start with.

Peter

 

[sheltonfilms]

Blower speed restrictions based on temperature have been around a long time. Ford implemented this on the 1995 Explorer by adding a physical sensor that mounted on top of the heater core and was connected directly to the EATC HVAC module. Since OBD-II came out in 1996 they just relied on the communication network to pull the value from the PCM where it was pulled from the regular coolant temp sensor.