Rear-window defrost DEFEAT feature?

[drudis]

Wanna turn off the rear window defroster heating, and keep it off – permanently.


When you set the heated seats on, or heated steering wheel, it turns on the rear-window defrost mode.

I don’t want/need that running, and know that is a 1mpg loss in fuel economy.

Not too big of deal, but 99% of the time, wife runs with these heat setting on, and barely 5% of the time would I ever need it, so why lose MPG.


QUESTION: Can I pull a fuse, or unplug the wiring to the defroster lines (cannot see it on window edge), to stop heating the dang window?

 

[Mlarv5]

Not sure what you are saying. By putting the heated seats and steering wheel on doesn't cause my rear defrost to come on. I have a 2017 but I don't think they changed the way those work over the years. Also how are you loosing MPG with running the rear defrost? It is electric and should not draw that much on the system to cause a MPG lose. Just trying to understand what you are asking
Mike

 

[drudis]

On older vehicles (brother's Taurus) he ran the rear-defrost on ALL THE TIME. When I told him about electrical draw and MPG... he gained 1-2MPG just by not running it at all.
Trying to duplicate that on the Explorer Sport, if possible.

 

[peterk9]

Wanna turn off the rear window defroster heating, and keep it off – permanently.


When you set the heated seats on, or heated steering wheel, it turns on the rear-window defrost mode.

I don’t want/need that running, and know that is a 1mpg loss in fuel economy.

Not too big of deal, but 99% of the time, wife runs with these heat setting on, and barely 5% of the time would I ever need it, so why lose MPG.


QUESTION: Can I pull a fuse, or unplug the wiring to the defroster lines (cannot see it on window edge), to stop heating the dang window?

I think it is more important to have a rear window that is clear than worrying about any potential negligible mpg loss.
On my Explorer, the rear defrost seems to be on at all times, regardless of other settings. If you check your Owner's Manual you will find that fuse #12 (40A) in the engine compartment fuse box is for the Rear Heated Window.

Peter

 

[CDW6212R]

I'd be that all rear defrosters are time limited, they only run for about five minutes when activated. I agree they shouldn't run continuously, and if they are active all the time the seats or steering wheel heater is on, I'd find a better control method too.

 

[thefranchise713]

I'm confused--rear window defrost is it's own control and my seats and heated SW don't drive that setting at all.

Even then, my rear window defrost times out after ten minutes or so.

 

[Mlarv5]

On older vehicles (brother's Taurus) he ran the rear-defrost on ALL THE TIME. When I told him about electrical draw and MPG... he gained 1-2MPG just by not running it at all.
Trying to duplicate that on the Explorer Sport, if possible.

The new vehicles they have a battery monitoring system. Which means they are only charging at the lowest possible amount. If you watch the volts going to the battery you will see the new ones charge anywhere from 12.5 to 14 volts as needed. I really don't think the rear defrost is on all the time. I know mine is only on when the switch is on and times out after about 5 or 10 minutes. I really don't think you will gain any MPG but let us know.

 

[Odrapnew]

Man, I'm glad I don't have a 2016, my rear defrost only runs when remote start or when I have rear defrost on. Doesn't run at all with heated seats.

As for impact on MPG, I'm guessing you couldn't actually measure it since other variables would have more of an impact.

 

[RhinoQuartz]

Rear defrost is definitely on a timer.

Edit: on mine anyway.

 

[peterk9]

The new vehicles they have a battery monitoring system. Which means they are only charging at the lowest possible amount. If you watch the volts going to the battery you will see the new ones charge anywhere from 12.5 to 14 volts as needed. I really don't think the rear defrost is on all the time. I know mine is only on when the switch is on and times out after about 5 or 10 minutes. I really don't think you will gain any MPG but let us know.

My defrost button is hardly used, yet I can clearly see that the rear window at times is defogging/defrosting without the button being in the ON position. I believe another member posted the same thing a while ago.

Peter

 

[KayGee]

On older vehicles (brother's Taurus) he ran the rear-defrost on ALL THE TIME. When I told him about electrical draw and MPG... he gained 1-2MPG just by not running it at all.
Trying to duplicate that on the Explorer Sport, if possible.

There is no way that running a electric grid style defroster on the rear glass of a vehicle is going to cause a 1-2MPG drop.

I think you are confusing the HVAC windshield defrost setting and the rear window defrost. Running the HVAC windshield defrost setting will run the AC system to dry the air (prevent fogging and moisture on inside of windshield) and can impact MPG.

 

[peterk9]

I was going to post the same thing until I did some checking on the Internet and found several articles that supported the claim that current draw, minimal as it may be, can have an affect on mileage figures.

Peter

 

[CDW6212R]

The electrical draw is minor for that one circuit, there will be no measurable difference in mileage even if you hot wired it to run all the time.

The AC clutch does effect mileage, but 1mpg might be all under constant use. BTW, the AC clutch does run at all times except when the AC controls are turned OFF, or to the VENT position.

 

[613GT500]

You bought a 5000lbs boat and worried about MPG?

 

[tlveik]

If you check your Owner's Manual you will find that fuse #12 (40A) in the engine compartment fuse box is for the Rear Heated Window.
Peter

40 amp fuse? Wild guess says the heater takes half that. At 14 volts, that's 280 watts. That's a little more than 1/3 horsepower. How many horsepower does it take to maintain cruise speed in an Explorer? Should be able to estimate the mileage hit.

 

[jade97]

The Rear Defrost on my 2016 only works when I press the rear window defrost button & it is only on for about 5 minutes. The only other item that is activated with the rear window defrost is my side mirror defrosters.

My heated seat buttons only activate my heated seats.

My heated steering wheel button only activate my heated steering wheel.

My AC seat buttons only activate my AC seats.

No fuel mileage affects......

My past 2011 worked the same way sans the AC Seat, Heated Seat, and Heated Wheel...since it was an XLT and not equipped.

 

[peterk9]

My 2011 Limited and 2014 MKT worked the same way. However, for some reason, my 2017 rear defrost/defog seems to be always ON. Not concerned about it.

Peter

 

[Mlarv5]

My 2011 Limited and 2014 MKT worked the same way. However, for some reason, my 2017 rear defrost/defog seems to be always ON. Not concerned about it.

Peter

I think I know why. You leave the climate control on Auto all the time. I have mine on manual so it is always off unless the button is pushed. If yours is not on Auto then I don't know.

Page 137 of OM

Auto setting
In cold weather, the system is set to 72°F
(22°C). The heated seats are set to high
(if available, and selected to AUTO in the
information display). The heated rear
window and heated mirrors automatically
turn on.
137

 

[RhinoQuartz]

I think I know why. You leave the climate control on Auto all the time. I have mine on manual so it is always off unless the button is pushed. If yours is not on Auto then I don't know.

Page 137 of OM

Auto setting
In cold weather, the system is set to 72°F
(22°C). The heated seats are set to high
(if available, and selected to AUTO in the
information display). The heated rear
window and heated mirrors automatically
turn on.
137

Well, isn't this ironic for Peter. Good find there.

 

[CDW6212R]

I think I know why. You leave the climate control on Auto all the time. I have mine on manual so it is always off unless the button is pushed. If yours is not on Auto then I don't know.

Page 137 of OM

Auto setting
In cold weather, the system is set to 72°F
(22°C). The heated seats are set to high
(if available, and selected to AUTO in the
information display). The heated rear
window and heated mirrors automatically
turn on.
137

That could be the root of a problem. I'd cut that circuit not long after I knew of it. There's no good reason to pass current through the rear defroster unless there's known frost on it.