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The problem with the climate control is the heating/cooling varies depending on the outside air temperature reading. Setting the controls for a particular temperature doesn't produce a consistent result because the system is constantly comparing that setting against the outside temp. For instance if I set the control to 70 and outside temp reads 60 the system blows warm air, but if the outside temp reads 75 the system blows cool air. That sounds logical, but in practice it's sometimes really annoying. The other thing is the temp setting changes in steps; for instance you can set it at 70 and it will be a little too cool, but when you move it to 71 it will start blowing warm air. I miss the simple system in the 2003 Elantra that ignored the outside temperature and just blew warm or cold air based on the position of the sliders. Is there a way to make the 2017 system work more like this?
 

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The Auto setting on your HVAC should read from ambient air temp sensors inside the vehicle, not outside. If the vehicle has sat several hours, the internal temp should eventually equalize to the same as the outside temp, which would make your example of whether it blows warm or cold on a 70deg setting correct. But, after it reaches an internal temp equal (approx) to your setting, it will adjust both temp and which vent it blows out of to maintain that setting regardless of external temp. If your vehicle is doing anything other than this, you may have an issue and should have it checked at your dealership.
 

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Also, you can turn off the auto function by pushing the Auto button on the left of your HVAC controls. While you don't have a slide with a blue and red setting, you can forgo the displayed temp reading and just turn the knob and push the blower buttons until you find a temp and pressure that is comfortable to you
 

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Your system may be malfunctioning. My '17 VE has the best auto climate control I've experienced in recent memory.
 

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In a MVAC system all the air passes through the evaporator first, then can either go directly to the vents or some of it bypassed through the heater core that should be at a constant temperature, its always hot, and should be at 195*F.

The output is sensed by an incar temperature sensor that is compared to a voltage determined by the dial control on the climate control panel. The differential voltage is the input to a servo circuit that rotates a so called blend door. That voltage can be either positive or negative to either open or close that blend door.

When dealing with temperature changes, this electromechanical system cannot be instantaneous, in particular when driving in wind gust situations. Yet another variable is where the intake air is coming from to the input of the evaporator, can either be from the so-called fresh air intake from the vents under the windshield, or from the cabin itself determined by the position or the recir door.

Not one door, but two, recir and blend., Problems do arise from a sticky blend door or a loose recir door, so cannot eliminate these possibilities that result in major temperature changes. But the air coming from the cabin is far more stable than the air coming from the fresh air intakes.

But even when working well will notice minor temperature changes if you are driving with the dash vents opened blowing directly in your face. Can't keep that recir door closed from outside air, under heating conditions below 59*F will only stay closed for five minutes. Only way to switch it closed again, is to reboot the engine starting sequence. Doing us a favor by not killing us with CO.

When driving longer distances, find these minor variations far less noticeable when switching to the floor vents. But also do notice temperature changes particularly in gusty wind situations when using the dash vents. Is even less noticeable when switching to the bi-level mode with your heater mode controls.

Blower speed also makes a difference.

Back in the older days, heat control was made by a cable controlled heater valve controlling the coolant flow through the heater core. Here the time delay was quite long, hated riding with my brother-in-law, just have to tap it a bit and wait several minutes, but he would jam that lever full so was either being baked alive or frozen to death.

These systems are history, the blend door operates a lot quicker, and automatic climate control that door is controlled by a servo, actually not new, had this in my 70 Buick.

Back in the 20's, first problem was finding a closed vehicle, most were opened, but tried using exhaust manifold heating, but were killing people with CO poisoning. Ironically still using this system today in aircraft, but made out of stainless steel with CO monitoring.

In my early 30's vehicles, no heater period, had to bring blankets, in the later 30's clear up to the 50's used just a heater core under the glove compartment door, controlled by a water valve, everybody was fighting to sit in that front passenger so-called death seat, only near warm seat in the car.

First vehicle to have AC was a 1939 Packard, had a huge AC package in place of the trunk of the car. In the early 50's Chrysler came out with the systems we have today, while a 52 De Soto was considered a nerd car, had one of those, was very comfortable.

AC did not become popular until around 1956, but only in a Cadillac, could get one in a 57 Chevy, but darn new doubled the price of the car. Today practically all cars have AC, even the basic ones, but for some weird reason, eliminating the cruise control switches.

My first car to have one was my 65 Buick, didn't want this toy before this, was far more interested in performance, but sure got spoiled by it. LOL, haven't owned a vehicle since then without AC, but compared to the 20's, we are sure getting soft.
 
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