Climate control

redwngr · November 5, 2014

In order for the AC to remove humidity during the heat cycle, the air would have to pass over the AC coils and cool down so the humidity condenses and then the air has to be heated back up to the set temperature before coming out of the vents. That seems like more work for the system to do than to just shut the AC off and run the heat by itself if MPG's are your primary concern. I'm not sure about the defrosting the windshield faster. I've never experimented with that but the windshield seems to clear up just fine once the air coming out of the vent is hot.

Yupp, that's exactly how it works.

When it's cold enough for 'frost' on the windshield (rather than 'fog') the ac will be off.

Isriam · November 7, 2014

just to bump this for more information:

if you edit the floor/vent/defrost it does turn off the auto system. The fan/temp will show auto but it no longer works in full auto. The temp is now based on the vent air temperature and not the vehicle temperature.

example, if you want the truck to be 72 degrees and it is 35 degrees outside, the full auto will make the vent air max temp to raise the truck inside temp to 72. however if the system is not on full auto and this same scenario, the vent air temp will only be 72 degrees and not max, so it takes longer to reach inside temperature of 72.

really a stupid design.

KARNUT · November 7, 2014

I grew up in New Jersey (don't miss it)and am old enough to have experience new cars and trucks without AC. I don't miss having to have a rag close by to wipe off the inside windows when it was damp and rainy, with out having the aid of the AC to take out the moisture. Its on even when you think its not, and you need it even when you think you don't, unless you live in the desert.

redwngr · November 7, 2014

just to bump this for more information:

if you edit the floor/vent/defrost it does turn off the auto system. The fan/temp will show auto but it no longer works in full auto. The temp is now based on the vent air temperature and not the vehicle temperature.

example, if you want the truck to be 72 degrees and it is 35 degrees outside, the full auto will make the vent air max temp to raise the truck inside temp to 72. however if the system is not on full auto and this same scenario, the vent air temp will only be 72 degrees and not max, so it takes longer to reach inside temperature of 72.

really a stupid design.

Now I'm going to have to check that on the new one when it arrives....

Jon A · November 8, 2014

if you edit the floor/vent/defrost it does turn off the auto system. The fan/temp will show auto but it no longer works in full auto. The temp is now based on the vent air temperature and not the vehicle temperature.

example, if you want the truck to be 72 degrees and it is 35 degrees outside, the full auto will make the vent air max temp to raise the truck inside temp to 72. however if the system is not on full auto and this same scenario, the vent air temp will only be 72 degrees and not max, so it takes longer to reach inside temperature of 72.

really a stupid design.

Thankfully, none of that is even remotely true. Do you have a thermometer? With the climate control set for 75 (but cabin temp in the low 70's so it was putting out some heat), I hit the defrost button. Air shifted to the defrost vents. I measured it at over 130 degrees. I manually cranked the fan to max. After a long time, temp still was over 130 degrees--with the "temp knob" still reading 75.

I swear, 90% of the "complaints" of the climate control setup in these things are more like "misunderstandings." Note to GM HVAC Engineers from Customer Service--next time around eliminate the little LED light for the A/C and customer satisfaction will improve 1000%! I've never seen so many complaints of a complete non-issue in my life.

Isriam · November 9, 2014

Thankfully, none of that is even remotely true. Do you have a thermometer? With the climate control set for 75 (but cabin temp in the low 70's so it was putting out some heat), I hit the defrost button. Air shifted to the defrost vents. I measured it at over 130 degrees. I manually cranked the fan to max. After a long time, temp still was over 130 degrees--with the "temp knob" still reading 75.

I swear, 90% of the "complaints" of the climate control setup in these things are more like "misunderstandings." Note to GM HVAC Engineers from Customer Service--next time around eliminate the little LED light for the A/C and customer satisfaction will improve 1000%! I've never seen so many complaints of a complete non-issue in my life.

actually i did, thanks for your concern. going from floor to vents, the temperature leaving the vents was 73 degrees while the ambient was 44 and the inside of the truck was 62.

ahahnu · November 10, 2014

I've tried the above suggestions. The warming the truck up and then adjusting the temp to 75...... works. It still gets too hot, and I'm not interested in having AC come out of the vents when it's cold out. I still want to turn the whole system off. No air or fan blowing anything coming out of the system. In my V I press recycle on any of the fan setting with system off and nothing comes out.

If no one knows I'm thinking of calling GMC or going to the dealer. It's pretty frustrating. I'm tired of it myself and all of my passengers have asked if there is anyway to shut it off.

Velocibiker · November 10, 2014

If no one knows I'm thinking of calling GMC or going to the dealer. It's pretty frustrating. I'm tired of it myself and all of my passengers have asked if there is anyway to shut it off.

The only thing that works on my Silverado is to turn on recirculate and vents. Then close the dash vents manually. Of course every time I shut off the truck, the recirculate is turned back off so I have to turn it back on every time. It's a bit annoying, but no worse than things on other cars/trucks I've owned.

I'm sure some of this is to allow the interior to 'breathe'. On my wife's Honda, the OM says "The system should be left in fresh air mode under almost all conditions. Keeping the system in recirculation mode, particularly with the A/C off, can cause the windows to fog up. Switch to recirculation mode when driving through dusty or smoky conditions, then return to fresh air mode." Then goes on to say: "Turning the fan speed control dial all the way to the left shuts the system off. ● Keep the system off for short periods only. ● To keep stale air and mustiness from collecting, you should have the fan running at all times". I figure our vehicles have similar logic behind the way it works. Engineers trying to save us from ourselves.

ahahnu · April 23, 2015

After a few road trips and some time to play with it, I've learned a few things about "my" complaints.

In cool weather, I warm the inside temp until I'm comfortable then adjust the "Auto" thermostat to 75. If I get too hot or cold adjust a degree or two at a time.

If I want 0 air at all I press the dash button so air would be forced out the dash, not the feet or defrost and press recycle. Nothing comes out at that point.

That's my story and I'm sticking to it. Thanks to all that helped. Can't wait for steady warmth to drive with the windows down.

TJay74 · April 23, 2015

I would make sure you have the newest calibration in your HVAC module, I had mine updated last month. Easiest way to tell is if you leave the system off and remote start and the system does not automatically start AC/heat then you have the early production calibration. The new one fixes that and makes the system operate like previous generation GM vehicles.

The G-Man · April 23, 2015

After a few road trips and some time to play with it, I've learned a few things about "my" complaints.

In cool weather, I warm the inside temp until I'm comfortable then adjust the "Auto" thermostat to 75. If I get too hot or cold adjust a degree or two at a time.

If I want 0 air at all I press the dash button so air would be forced out the dash, not the feet or defrost and press recycle. Nothing comes out at that point.

That's my story and I'm sticking to it. Thanks to all that helped. Can't wait for steady warmth to drive with the windows down.

If you want 0 air can't you just press the power button on the fan knob? That's what I do and it works. I only use it with windows down, otherwise I'm on auto all the time.

SouthpawHD · April 23, 2015

The only complaint I have with the system is that on bright, sunny days the A/C can turn on and blow cool air even though the outside temp might be onl 40*. But I understand why it does that, as it's all about the inside temp. Just odd and takes some getting used to.

On mild days, I simply push the knob in the middle and turn the whole thing off. It's a rather simple design and easy to work with.

TJay74 · April 23, 2015

If you want 0 air can't you just press the power button on the fan knob? That's what I do and it works. I only use it with windows down, otherwise I'm on auto all the time.

Even though you turn the system off via the dash, if the recir door is left open then when outside air hits the windshield pickup point it will force the air across the heating/cooling system and will cause warm/hot air to come out the vents. Only way around this is to either close the vents which then will defeat the auto HVAC under remote start or else close the recir doors via the HVAC button.

The G-Man · April 23, 2015

Even though you turn the system off via the dash, if the recir door is left open then when outside air hits the windshield pickup point it will force the air across the heating/cooling system and will cause warm/hot air to come out the vents. Only way around this is to either close the vents which then will defeat the auto HVAC under remote start or else close the recir doors via the HVAC button.

OOOOOOOOO. Got it. I suppose some people want a sealed cabin? The question is this now: is this air ambient temp or is it picking up temperature as it moves across the heater core/AC evaporator?

TJay74 · April 23, 2015

Probable a little of both, lets say you have the dial set on 60° as an example. The blend door will be directing the airflow across the evaporator coil. Since the coil is not in use with Freon running thru it that air will pick up the ambient temps of the evaporator as well as what ever the outside temps are as well.

Even with outside temps in the 60's my vent temps with the dial set at 60° are still on the warm side. During the summer months I will direct the dash vents away from my face since I drive with the windows down, this way I can still use the auto HVAC mode as well.