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Discussion Starter · #1 ·
I've noticed something annoying about the front defog system in my '16 Volt, and would like to know if anyone else has experienced this.

Today it was about 65 degrees out and raining pretty hard. I didn't need climate control, so I turned it off. When the windshield started to fog, I pressed the regular defog button and made sure that the eco and max climate control modes were both off (i.e., the defogger was blowing unconditioned air from the outside).

So far so good. Soon I realize the windshield isn't defogging fast enough, so I press the Max Defog button. The a/c kicks in and it clears the windshield in seconds, like it should. But now I'm freezing. So I press the regular defog button. But the a/c continues to be on - the system does not revert to blowing unconditioned air. This goes on for many minutes, long after any residual cold air from a brief a/c on period should have blown out. The only way to turn off the a/c at this point seems to be to turn off the climate control system entirely (no fan, completely off) or turn off the car and turn it on again.

This is really annoying - any ideas as to what's going on here?
 

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I've noticed something annoying about the front defog system in my '16 Volt, and would like to know if anyone else has experienced this.

Today it was about 65 degrees out and raining pretty hard. I didn't need climate control, so I turned it off. When the windshield started to fog, I pressed the regular defog button and made sure that the eco and max climate control modes were both off (i.e., the defogger was blowing unconditioned air from the outside).

So far so good. Soon I realize the windshield isn't defogging fast enough, so I press the Max Defog button. The a/c kicks in and it clears the windshield in seconds, like it should. But now I'm freezing. So I press the regular defog button. But the a/c continues to be on - the system does not revert to blowing unconditioned air. This goes on for many minutes, long after any residual cold air from a brief a/c on period should have blown out. The only way to turn off the a/c at this point seems to be to turn off the climate control system entirely (no fan, completely off) or turn off the car and turn it on again.

This is really annoying - any ideas as to what's going on here?
Do you have the Auto Defog setting set to On? When set to On, the front defog will automatically come on when the vehicle is started. I leave the Auto defog set to On and I have experienced the Max AC coming on automatically, air recirculate setting being automatically turned from On to Off if the climate control system detects high humidity while the Volt is running. With Auto Defog set to On the Volt's climate control system will do whatever it needs to do to defog the windshield, keep it from re-fogging.
 

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I remember a lot of discussion on gen 1s abt when the humidity sensor causes the A/C to run. Just reviewed for the 2107 gen 2 (probably similar to the 2016) (essentially what jcanoe said):

158 Climate Controls

When in Fan Only mode, if Auto
Defog is enabled, the air
conditioning and electric heat may
turn on when high humidity
conditions exist. See “Climate and
Air Quality” under Vehicle
Personalization 141 for more
information on the Auto Defog
selection. The air conditioning may
also run if MAX is selected.

160 Climate Controls

Auto Defog : The system will
monitor high humidity inside the
vehicle. When high humidity is
detected, the climate control system
may adjust to outside air supply and
turn on the air conditioner or the
heater. The fan speed may slightly
increase to help prevent fogging.
When high humidity is no longer
detected, the system will return to
its prior operation. To turn Auto
Defog off or on, see “Climate and
Air Quality” under Vehicle
Personalization 141.

Climate Controls 161

Humidity Sensor
The humidity sensor is near the
base of the inside rearview mirror.
The climate control system uses the
sensor information to adjust the
temperature and recirculation for
best comfort.
 

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This is really annoying - any ideas as to what's going on here?
And this is exactly why I don't try to outsmart the climate control and just leave it on automatic everything. If you stop trying to manage the car and just tell it what you want, you'll get it. If it's on "automatic," the car will balance all that stuff FOR YOU.
 

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Discussion Starter · #6 ·
Do you have the Auto Defog setting set to On?
No, it's off because I can't stand the a/c coming on when I didn't ask for it.


When you pushed the Max Defog button I believe it automatically activates the Max climate control button.

After you pushed the regular defog button did you check that eco or max was not on?
Neither Max nor Eco is on after I push the regular defog button.


And this is exactly why I don't try to outsmart the climate control and just leave it on automatic everything. If you stop trying to manage the car and just tell it what you want, you'll get it. If it's on "automatic," the car will balance all that stuff FOR YOU.
Yes, that works well when the temperature actually needs to be adjusted. When it's 68 degrees outside, I am perfectly happy with the temperature inside the car. The problem is that if it's both 68 degrees and raining, the only way to get effective defogging is to turn the a/c on - and then I end up freezing. Or I guess I could turn the heat on by setting my temperature preference to something much higher than 68 degrees - but in humid weather, that's not very comfortable, either.

Anyway, the workaround I've developed is to leave the regular defog on, don't touch the max defog button, and just press "eco" whenever the windshield fogs up (with temperature set to 69 or 70). That turns the a/c on, the windshield clears, and then I press "eco" again to turn the a/c off. This works reasonably well (the a/c actually goes off, unlike when I use the max defog button), but it still gets too cold in the car.

And I'm still curious whether anyone else has observed this refusal of a/c to turn off after turning off max defog. I'm guessing this is a bug, not a feature, but is it a bug in all gen 2 Volts, or just mine?
 

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When it's 68 degrees outside, I am perfectly happy with the temperature inside the car. The problem is that if it's both 68 degrees and raining, the only way to get effective defogging is to turn the a/c on - and then I end up freezing. Or I guess I could turn the heat on by setting my temperature preference to something much higher than 68 degrees - but in humid weather, that's not very comfortable, either.
I really think your attempt to micromanage the climate control system is the cause of your frustrations. Probably the first thing to understand is that it's not really feasible to leave the temperature setting at the same level in all conditions. You're going to need to set it lower in bright sunlight and higher in damp rainy conditions. If you just let the climate control system manage HOW to get the desired temperature and keep the windows clear, you'll quickly get a good idea of where you need to set the temperature to be comfortable.

Don't forget that the system will turn on the A/C AND the heat for defogging - the A/C wrings the humidity out of the air and then the heat raises its temperature so that it can hold more moisture - that combination of dry, warm air is what makes the defogger so effective.
 

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I wonder if the Volt manages A/C compressor cycling for efficiency and/or compressor life (as to why it might be running a little longer than expected)? When auto doesn't do the job for me, I just go to max and crank up the heat if I feel cold.

Last time I struggled with defog methods, I think outside versus recirculate made the biggest difference.
 

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Discussion Starter · #9 ·
Don't forget that the system will turn on the A/C AND the heat for defogging - the A/C wrings the humidity out of the air and then the heat raises its temperature so that it can hold more moisture - that combination of dry, warm air is what makes the defogger so effective.
So according to this, if it's 68 degrees out and raining, I should set the temp to something considerably warmer than 68, set Max Defog, and I will get a combination of a/c and heat that will both defog the windshield and keep the temperature comfortable.

That makes sense, but we are back to the problem I identified to begin with: once I turn Max Defog on, I can't turn off the a/c without turning off the car. So if it stops raining and I no longer need defogging, I'm stuck wasting a lot of energy running both heat and a/c to keep the temperature comfortable.
 

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So according to this, if it's 68 degrees out and raining, I should set the temp to something considerably warmer than 68, set Max Defog, and I will get a combination of a/c and heat that will both defog the windshield and keep the temperature comfortable.
Well I don't have a Volt so I can't claim in any detail how its HVAC system is programmed - but in the cars I've been driving "Max Defog" overrides everything else, including your temperature setting. But on the other hand you generally only need it briefly - in my car the system's temperature and humidity sensors do a great job of keeping the windshield clear once the initial condensation has been eliminated.

That makes sense, but we are back to the problem I identified to begin with: once I turn Max Defog on, I can't turn off the a/c without turning off the car.
That doesn't make any sense to me. Can't you just press "Max Defog" again to toggle it back off?
 

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That doesn't make any sense to me. Can't you just press "Max Defog" again to toggle it back off?
Without actually testing it with the hood open, this is how my 2017 seems to work. A second press of the Max Defog button turns it off. I'm pretty sure that if the A/C stays on, I can turn it off with the Eco or Max buttons.
 

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Discussion Starter · #12 ·
Well I don't have a Volt so I can't claim in any detail how its HVAC system is programmed - but in the cars I've been driving "Max Defog" overrides everything else, including your temperature setting. But on the other hand you generally only need it briefly - in my car the system's temperature and humidity sensors do a great job of keeping the windshield clear once the initial condensation has been eliminated.


That doesn't make any sense to me. Can't you just press "Max Defog" again to toggle it back off?
Without actually testing it with the hood open, this is how my 2017 seems to work. A second press of the Max Defog button turns it off. I'm pretty sure that if the A/C stays on, I can turn it off with the Eco or Max buttons.
If I recall correctly, a second press of the Max Defog button does *not* turn the Max Defog LED off. That always seemed odd to me. I get the LED to turn off by pressing the regular defog button, or pressing "auto". But that seems to just turn the LED off, not the actual a/c.

It's beginning to sound like this is a bug that I need to get the dealer to look at.
 

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If I recall correctly, a second press of the Max Defog button does *not* turn the Max Defog LED off. That always seemed odd to me. I get the LED to turn off by pressing the regular defog button, or pressing "auto". But that seems to just turn the LED off, not the actual a/c.

It's beginning to sound like this is a bug that I need to get the dealer to look at.
I tested my Max Defog button today. First push turns it on, second push turned it off. Not sure if the A/C actually turned on/off, but the LED did.
Also the regular defog button only changes the air flow to windshield only, I don't think it will control the A/C.
Pressing the "Auto" button may or may not turn on/off the A/C. Depends on the temperature setting, outside air temp, and inside air temp.
 
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