HVAC...all hot or all cold

[DocHolliday]

I notice that my temp control has very little in between temp selection, it will get hot but when turned down in increments of 1 degree there is no change in it coming from the vent till all of a sudden it blows cold. Dealer said they monitored the air coming out and indeed there is little to no middle temps. They also tested several other Tahoes on the lot and said they all do the same thing. They went on to say it doesn't seem right, but thats the way it is.

Anyone else notice their air temp doing this? i.e. very little intermediate temperatures?

 

[Reels]

It would be difficult to regulate the temp of the air coming out. In all my denalis current and past heat or cold comes out and the fan speed controls getting to the programmed temp in the cabin by pumping more or less air.

 

[DocHolliday]

It would be difficult to regulate the temp of the air coming out. In all my denalis current and past heat or cold comes out and the fan speed controls getting to the programmed temp in the cabin by pumping more or less air.

I would have to respectfully disagree. The temp is absolutely adjustable, fan speed doesn't set temp in the car.

 

[kcb14214]

I have the same issue, freeze or sweat. And off doesn't equal off. The vents bleed almost as if the fan was on high when I turn mine off.

 

[Reels]

I could be wrong as it has been a long time since I wrenched so this is an old school description. Maybe a mechanic onboard can explain if the newer systems are different. I am always eager to learn new things.

Here is what I would think is the system in its basic form.

Hot coolant passing through the heater core gives off heat before returning to the engine cooling circuit. The fan for the vehicle's ventilation system forces air through the heater core to transfer heat from the coolant to the cabin air, which is directed into the vehicle through vents at various points.

 

[DocHolliday]

I have the same issue, freeze or sweat. And off doesn't equal off. The vents bleed almost as if the fan was on high when I turn mine off.

Same....off does not equal off. The hot air continues to seep out causing me to open the windows and circulate some cold air in. This should happen on a 75k vehicle.

---------- Post added at 09:08 AM ---------- Previous post was at 09:05 AM ----------

I could be wrong as it has been a long time since I wrenched so this is an old school description. Maybe a mechanic onboard can explain if the newer systems are different. I am always eager to learn new things.

Here is what I would think is the system in its basic form.

Hot coolant passing through the heater core gives off heat before returning to the engine cooling circuit. The fan for the vehicle's ventilation system forces air through the heater core to transfer heat from the coolant to the cabin air, which is directed into the vehicle through vents at various points.

You're on the right track, there is also a "mixing vent" that allows ambient cooling air to be added to the system and into the cabin which is how the temp of the air is supposed to modulate.

I think your opinion or understanding was cabin temp was adjusted by simply changing the amount of max hot air introduced to the cabin. That's not 100% correct, it really is more sophisticated that that.