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Ford Fusion Energi Forum

Rear defrost always on (when below 0C // 32F)


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I was driving home today, and it's -1C (30F) and there's a light snowfall. I noticed that while the rest of my car was covered in snow, the rear window was clear. I pulled over and sprinkled some more snow on, and before you know it, it melts -- and, it has the characteristic rear defrost melt pattern (lines across the glass).

 

The thing is, my climate control system is on AUTO (21C), and my rear defrost is OFF!! I thought AUTO only adjusts the air heating not the rear defroster...

 

What I'm wondering is, is there some sort of temperature threshold so that the rear glass defrost is automatically turned on (even without the switch being pressed or illuminated)? Does anyone else find this to happen to their vehicles?

 

I'm guessing that this would have a profound impact on range.

 

The other day, when it was a few degrees warmer, I had at least 10km of additional range. Today, however, with the same battery charge, and a few degrees colder, my range is down as well -- and maybe, just maybe, this is attributed to our cars having the defrost automatically turn on.

 

Thoughts?

Edited by profskule
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  • 2 weeks later...

Update!

 

I went to the dealer and after a diagnostic they said that all Ford Fusion Energi automatically turn on their rear defroster and side mirror defrosters when the temperature outside falls below 0C (freezing). The rationale is that this adds a load to the system prompting the IC engine to turn on, leading to a faster warm up time. The LED button light will remain unlit.

 

How silly is this, eh?

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Update!

 

I went to the dealer and after a diagnostic they said that all Ford Fusion Energi automatically turn on their rear defroster and side mirror defrosters when the temperature outside falls below 0C (freezing). The rationale is that this adds a load to the system prompting the IC engine to turn on, leading to a faster warm up time. The LED button light will remain unlit.

 

How silly is this, eh?

My 2013 does not do that.

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