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HVAC controls - explain like I'm 5.

LS 1st Gen

By LS 1st Gen
in Troubleshooting & Recalls

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TmartinD Enthusiast

TmartinD

Posted
Posted
not sure on exactly how the hvac system works 100% but i do know that the hvac system does use the compressor and it's supporting parts to "dry" the air and keep the moisture out of the cabin.

 

No wonder I get shocked every time I get out of the truck. Plus, cloth seats don't help.

GM Dude Enthusiast

GM Dude

Posted
Posted

I'm having the same problems. Get in the truck and it may be 65 deg in the cab, have the controls set at 72, start the truck and blower comes on high speed and will blow cold air (even after the engine warms) until I turn auto off and then turn it back on and it will get warm. WOW, what gives GM?

tbarn Senior Enthusiast

tbarn

Posted
Posted

The following conditions must be met in order to activate the A/C compressor:

  • Battery voltage is between 9–18 V
  • Engine coolant temperature is less than 124°C (255°F)
  • Engine speed is greater than 600 RPM
  • Engine speed is less than 5 500 RPM
  • A/C high side pressure is between 269–2 929 kPa (39–425 PSI)
  • Throttle position is less than 100%
  • Evaporator temperature is greater than 3°C (38°F)
  • ECM does not detect immoderate torque load
  • ECM does not detect insufficient idle quality
  • The ambient temperature is above 1°C (34°F)
Sir Dan Enthusiast

Sir Dan

Posted
Posted

On my GMT900, the compressor will run when any window defrost mode is selected even if the a/c indicator light is off. I think that is a safety thing to keep windows clear. On panel or floor modes, I can turn the compressor on and off at will. Probably the same on the new ones.

cmpcpro Enthusiast

cmpcpro

Posted
Posted

On this truck whenever I have recirc on the AC comes on.. so if I don't want the AC on I have to have recirc off and then every smell I drive through comes right in the truck..

  • 4 months later...
caveat71 Enthusiast

caveat71

Posted
Posted

I'm trying to figure this out myself...my 2010 GMC Acadia has the "auto" option which when activated turns on the A/C. I get that. When I just want to use outside air on auto (e.g. outside air is << inside air temp) I hit the A/C button and it turns off the compressor and just uses 'fresh air'

 

On my 2014 Sierra...I press "Auto" and as expected I get A/C cooling. Perfect. When I press the A/C button to turn the compressor off (as in the 2010) nothing happens and it keeps cooling the vehicle with A/C. If I turn the HVAC off and then back on, the system remains in "auto" mode for the blower, and now as expected the compressor is off.

 

Is this a defect, or is it how its intended to work?

scott19677 Senior Enthusiast

scott19677

Posted
Posted

I whish I had my old KNOB back. Blue=cool.Red=warm. "IF IT AINT BROKE, DONT FIX IT'. I wanted a new TRUCK. Not an excerise in engineering. Stupid nerds. :idiot:

kurtg2020 Enthusiast

kurtg2020

Posted
Posted

Question about the HVAC system, can you turn it completely off? This morning on my way to work, it was 64 outside, I had my HVAC system off, but the temp on the gages still show, they were set to 72. The truck was blowing warm air, I turned the temp down to 68, and it blew cooler air even though the system was suppose to be off.

  • 1 year later...
glnisbet Enthusiast

glnisbet

Posted
Posted

I too do not understnad the setup Hit AUTO and set temperaure at 68 and at 40 degrees outside AC liht od cold air from the vents.

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chuckl1218 Senior Enthusiast

chuckl1218

Posted
Posted

In Auto, the AC light will be on, but this does not mean the compressor is on unless it is dehumidifying, like when it is raining out or truly cooling when the ambient temp is warmer in the cab than outside.

 

With this system, I basically set temp (I like 71; wife likes 73) and leave it on Auto all of the time. But I am not one to drive with the windows open due to severe allergies. If you can get used to the truck determining when to heat, cool, high fan, low fan and not worry about the temp coming out of the vents at any given time, this works. If not, then I can truly understand how frustrating it can be to figure out.

ic3man5 Enthusiast

ic3man5

Posted
Posted

Quoted from my post (http://www.gm-trucks.com/forums/topic/178261-2015-silverado-auto-climate-system-and-ac-onoff/?do=findComment&comment=1695879):

 

 

So I managed to play around with the system a bit today I was curious if the AC actually shut off when in auto mode (The light is always on when in auto). Here are my findings:

-It seems like it will turn off under certain conditions but for the most part its 95% of the time on.

-It Seemed like between 75-80ish it would turn off, anything above 80+ it would kick it back on and push it to the defroster. Seems like if the auto system is pushing out of the front vents you have a good chance it "might" be off.

-If you push the vent selector when its in auto mode it will keep the fan in auto mode until you turn the fan knob.

-The Circulate Air (cabin only) button doesn't turn the AC on at all if it wasn't already on in any mode.

-A/C OFF, Floor Only turns AC on (I'm convinced this is a software bug).

-A/C OFF, Floor and Defroster (Top vents) turns AC on.

-A/C OFF, Face/Front Only keeps AC off.

-A/C OFF, Face/Front and Floor keeps AC off.

The ones in bold above are the only guaranteed states the AC is off.

ic3man5 Enthusiast

ic3man5

Posted
Posted

I too do not understnad the setup Hit AUTO and set temperaure at 68 and at 40 degrees outside AC liht od cold air from the vents.

 

Its cold or hot depending on the inside temperature not the outside temperature. If your cabin is 70 and its set for 68 it will blow out cold air to try and drop the temperature. Its a very aggressive cold/hot setup.

Rock1500 Senior Enthusiast

Rock1500

Posted
Posted

I noticed the same issue over the winter and so I set it to manual with the temp set at 74. Once it's too warm in the cab, I then start turning down the temp or turn it off. If I go below 71, it feels like cold air is blowing. It made no sense how this worked. Glad I am not alone.

 

Sent from my SM-N900V using Tapatalk

  • 3 weeks later...
Rme2513 Enthusiast

Rme2513

Posted
Posted

As long as it not in auto or in the window defrost setting it will not come on with the AC light off

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