Beware Max Defrost

[Frost]

I live in cold country. We're having an old fashioned winter here with lots of single digit temps over the last few weeks, below zero not unusual. Today was a balmy 25 degrees, felt like spring and just an inch or so of light fluffy snow. Had to do some chores, started the truck and pushed max defrost for the first time. and got out to brush the snow off. Went back inside house for a moment. Total time of less than 5 minutes from starting truck to getting back in to leave.
Cracked windshield from bottom left to center of driver viewing area, probably 18-20 inches. Max defrost is a powerful blast. I'm usually wary of regular defrost in very cold temps for this reason, but wasn't real cold today. Max defrost seems a bit of overkill doesn't it?
You get into your 70's and hope that lesson learning slows down, guess not.

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[PltFX4]

Good advise!! 20 here but tomorrow -6 and Monday -10...

 

[Tom_C]

That's a bummer. I don't use it myself, but we don't get those kind of temps usually, and I also have a garage. I'll be sure to keep that in mind.

 

[airline tech]

I don’t think Max Defrost is the root cause, The windshield had to have a rock chip in it - creating a weak point. A close inspection of the crack will most likely reveal a chip at one end of the crack.

 

[LaBalbe]

I have to agree with @airline tech ; I've used Max Defrost several times in the winter over the years, and never had an issue with it. As you can see from my picture & location, we're no strangers to cold weather and snow.
There must have been some default in the windshield that weakened it and made it more susceptible to the temperature variation.
My sister has had to replace the windshield in her current car a ridiculous number of times (I think it's at 5 in 8 years, now), once getting a new crack on the drive home from having the windshield replaced. It doesn't seem to be a common issue with her make & model, so I suspect that there's a defect in the windshield frame which is somehow making her windshields more vulnerable.

 

[KNI]

Use the heated front window button instead of defrost. It keeps the temperature gradient stable accross the windshield so it does not crack.

 

[Frost]

Makes sense that there was a chip where it started. I only looked from the inside and crack began behind inspection sticker,I'll look closer tomorrow.
Never used max defrost before,didn't know it sets to 85 degrees and pumps so hard. That's a lot of heat on a wintry windshield regardless of any fault. Life happens though,just thought I'd pass this along.

 

[Muscleford]

I agree with @airlinetech, there is likely some other root cause.

 

[airline tech]

Use the heated front window button instead of defrost. It keeps the temperature gradient stable accross the windshield so it does not crack.

There is not a Heated FRONT window button, that is for Rear Defrost & Heated (OS) Mirrors.
There is however a small heater grid (defrost) for the IPMA Camera, and it is only a very small portion of the window (just in front of the Rear View Mirror)
It is not user controlled and its automatically controlled by the IPMA Module, to defog the area in front of the camera only.

The HVAC - Defrost vents are the only (Full Coverage) windshield heat supply.

In Defrost Mode - The Temp supply will be as (set) by you (Current Setting) and blower speed if in (Auto) will ramp up to whatever speed it needs to adjust to temp quickly.

In Max-Defrost - The Rear Window Heat & Mirrors are automatically (Triggered-ON)
The Temp Selection will (Automatically) change to (HI-90 Deg) and the blower motor will ramp up to (MAX) speed. I am approximating (90 Deg) as the increments are 5 Deg steps and it goes from 85 to HI. (So, HI - I would say is 90-Deg)

 

[DukeCanBuildit]

Makes sense that there was a chip where it started. I only looked from the inside and crack began behind inspection sticker,I'll look closer tomorrow.
Never used max defrost before,didn't know it sets to 85 degrees and pumps so hard. That's a lot of heat on a wintry windshield regardless of any fault. Life happens though,just thought I'd pass this along.

Your advice is still sound - wise to avoid it in case there is a small rock chip or crack you haven’t noticed. ?

 

[Frenchy]

I'm going to take a wild guess and state that your windshield already had a chip in it or small crack already. Since you started the truck with it on max defrost to begin with, you started out with a cold temperature coming out of the vents. Once the truck started warming up the heat gradually came up with no problems. With doing this you usually don't have this problem. Because you most likely already had a damaged windshield, this was going to happen one way or another anyways.

 

[IdahoRanger]

I don’t think Max Defrost is the root cause, The windshield had to have a rock chip in it - creating a weak point. A close inspection of the crack will most likely reveal a chip at one end of the crack.

Agree, must have had a weak spot or rock chip.

 

[Muscleford]

The person that made comment about the heated front window button is in Finland, maybe they have a heated front window over there.

 

[KNI]

The person that made comment about the heated front window button is in Finland, maybe they have a heated front window over there.

We do.

Might be a ROW thing.

 

[airline tech]

We do.

Might be a ROW thing.

I apologize

Forgive me for not catching that

So, is this an actual (Heater Grid) in the windshield or is it just the name the (ROW) Rangers use for Defrost?

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