Heater Operation Question

rangerhgm · April 1, 2017

17 Silverado with dual climate control

Outside temp was 42.

I was driving today and had the heat and fan turned totally off, but noticed it was getting really warm in the truck and there was hot air coming out of the driver side window vent.

I turned on the heat and it was set at 73 so I turned it down to 66 and turned it off again. No more air coming out of the side window vent.

Doesn't seem normal?

In my 07 GMC when I turned off the heat it was turned off and no air came out of the vents at all.

Luster · April 2, 2017

I haven't quite figured out the dual temp controls completely.

But... regardless of outside temp, when I have the driver or passenger side set to 73 or lower, I'm getting cool air, 74 or higher, I get heated air, so that seems to be the break point.

Maybe someone else can chime in with better info.

Thomcat · April 2, 2017

I've got mine figured out; it does whatever it wants to do. Try manually hitting recirc before turning it off to close the vent. If the ignition is turned off while the servos have the driver vent and outside air vent open, that is the position it will stay in even if manually turned off. And unless you retart the HVAC or hit recirc. it appears the default position is to leave the vent open.

Batfish · April 2, 2017

It should do whatever it needs to do in order to get to the setting.

rangerhgm · April 2, 2017

I haven't quite figured out the dual temp controls completely.

But... regardless of outside temp, when I have the driver or passenger side set to 73 or lower, I'm getting cool air, 74 or higher, I get heated air, so that seems to be the break point.

Maybe someone else can chime in with better info.

So, when you're getting cool/heated air blowing, are your controls turned totally off? Seems like if we turn every thing off no air would be blowing. I've never had the heating/cooling work like this in any vehicle I've ever owned.

Static · April 2, 2017

It doesn't really work like that. If you turn it off air will still blow. The blower isn't running but the faster you drive the harder it blows. I don't fully understand it but my 07 and my 10 both did this as well as my 05 work van. The temp control will work too to a point. It will allow heat to blow but will not adjust cooler than the outside air temp.

Luster · April 2, 2017

So, when you're getting cool/heated air blowing, are your controls turned totally off? Seems like if we turn every thing off no air would be blowing. I've never had the heating/cooling work like this in any vehicle I've ever owned.

It doesn't really work like that. If you turn it off air will still blow. The blower isn't running but the faster you drive the harder it blows. I don't fully understand it but my 07 and my 10 both did this as well as my 05 work van. The temp control will work too to a point. It will allow heat to blow but will not adjust cooler than the outside air temp.

Yes, even with system turned completely off, there is still air flow.

GM started using this in the 1963 Corvette and it evolved into all their models and brands by the early 70's. They used to call it "Flow-Thru-Ventilation". Keeps a certain amount of fresh air moving through the cabin. Helps to eliminate interior odors, musty smells, etc.

I've owned lots of Chevy's and Pontiacs and they all did this.

rangerhgm · April 3, 2017

Thanks guys.....Makes a little more sense, but still have a couple of questions.

I can understand the "flow thru", but what I don't understand is why was the air hot when the outside temp was 42?

Apparently the flow thru air temp isn't simply air coming in from outside because it was 42 outside and the air coming from the side vent was hot.

Is the temp of flow thru air controlled by what the temp controls were last set at?

I was comfortable to start with with out the heater on, but after a short drive it got too warm in the cab with the hot air blowing out of the side vents.

Static · April 3, 2017

sort of, It will not blow cooler then the outside air temp but if you turn the knobs to a warmer setting it will heat up as using the heater core uses no power.

Thomcat · April 3, 2017

Yes, even with system turned completely off, there is still air flow.

GM started using this in the 1963 Corvette and it evolved into all their models and brands by the early 70's. They used to call it "Flow-Thru-Ventilation". Keeps a certain amount of fresh air moving through the cabin. Helps to eliminate interior odors, musty smells, etc.

I've owned lots of Chevy's and Pontiacs and they all did this.

What we have now is not exactly the "flow through" ventilation of the early 60s/70s. That system had the fan running on an ultra low speed with the vent open everytime the ignition was turned on. There was air flowing from the vents in the HVAC off position even while the vehicle was not moving., the only way to turn the fan off was to pull the fan fuse. Commercials of the day showed a smoke bomb placed into a closed parked vehicle and the cabin cleared under positive ventilation in under two minutes. In the current system when the fan is in the off position the fan is off. In addition the older FTV systems used vacuum operated servos to operate damper doors on the outside air and the vents.....when the engine was turned off the vacuum signal died and the vent doors returned to a zeroed position.....as soon as you cut power to the current system the digital motor servos remain in their last position until power is restored or a new signal is sent.

But even when you are permitted to use the recirc control which is not possible under certain HVAC combinations; there is no way to positively seal the vent to prevent exclusion of all outside air, but using it before turning off the HVAC will greatly reduce the bleed through at speed. I have to hear crap from the wife every time we pass a dead skunk. Systems in my older Chryslers made more sense, you could mount a dead rat on the cowl and with the vent closed, not a whiff. And just what does GM ope to accomplish with this? Old commercials touted increased safety from CO asphyxiation from leaking vehicile tailpipes which is probably a load of crap.....if there was any safety concerns related to this NTHSA would have mandated FTV in all new vehicles a long time ago