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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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LS 1st Gen Enthusiast

LS 1st Gen

Posted
Posted

So I'm a little confused on the HVAC controls on my LTZ. In the good old days (GMT-400 and maybe 800's) you could switch the AC compressor off by pushing the AC button, no matter how hot or cold you set the temp knob or button to. On the current truck that doesn't seem to be the case. If I set the temp to say, 67, the truck keeps on cooling it seems, no matter if I have AC button on or not. So what gives? Obviously the HVAC system is basically doing its own thing to keep the temp where I set it. This is with the system NOT set to auto, btw.

 

Can someone in the know shed some light on the technical operation of the system? Maybe a PDF from GM explains it somewhere?

Audioi Enthusiast

Audioi

Posted
Posted

It runs the compressor almost all the time to keep windows clean.

thewhitestallion Senior Enthusiast

thewhitestallion

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.

Retired Bob Enthusiast

Retired Bob

Posted
Posted

On my new Silverado the HVAC does whatever it wants. In AUTO and the outside temp 42 I might have the desired temp to 68 but the system blows cold air into the cab. So I turn the desired temp up 1 degree to see if that produces warm air to the cab and that action will cause the fan to change to high speed. But it does not seem to produce the warm air?? I seem to have better luck when not using AUTO - not always what I want temperature wise, but better than with AUTO. I traded in a truck that had a knob I turned - Blue for cooler and Red for warmer - worked perfect. I could even change the fan speed with a separate knob!

redwngr Senior Enthusiast

redwngr

Posted
Posted

I always thought that the light indicates that compressor is enabled, not necessarily that it is running. And yes, it does run it for humidity control reasons some times.

 

If you take the temp control off of auto, you should be able to 'turn off' the light. (try setting it to 'vent')

tbarn Senior Enthusiast

tbarn

Posted
Posted

I always thought that the light indicates that compressor is enabled, not necessarily that it is running. And yes, it does run it for humidity control reasons some times.

 

If you take the temp control off of auto, you should be able to 'turn off' the light. (try setting it to 'vent')

 

Bingo. Light means enabled. May or may not run depending on a multitude of criteria. For one, cold ambient temp means reduced system pressure. With reducued system pressure, A/C compressor engagement is disabled.

pm26 Senior Enthusiast

pm26

Posted
Posted

I always liked manual A/C systems. I am not too lazy to adjust the temperature by turning a knob. If I get a fully automatic system, as least I want a manual mode.

dmd277 Enthusiast

dmd277

Posted
Posted

I keep my HVAC in manual during the winter with the AC off. IF I want heat I turn down the temp until if produces warm air, then are the temp gets comfortably I turn if up a few degrees. I actually prefer a manual temperature control over the auto. Have not need AC yet.

fondupot Senior Enthusiast

fondupot

Posted
Posted

What i've found in the winters is that if you hit auto and then press the AC button to turn that off, the fans will stay in auto mode, but the temp will blow warmer air. Usually have mine set on 70-72 when it was really cold out this winter.

mike94silverado Senior Enthusiast

mike94silverado

Posted
Posted

Its Auto for a reason..... actually keeping the compressor in use helps it last longer... we had so many a/c failures in my area simply because it was only used 3 months a year.... now you're seeing 10-15 year old vehicles with auto still working well.....

tanner709 Enthusiast

tanner709

Posted
Posted

It's horrible the temperature is so erratic and all over the place in either mode. Set it for 21C it blows cool air set it for 22 it blows HOT in manual. Auto doesn't let the compressor turn off, and seems to be cooler than the indicated temperature even when it's switched off.

I agree with a lot of comments in here...keep it simple GM frig sakes. Another flawed and poorly tested system on this truck.

redwngr Senior Enthusiast

redwngr

Posted
Posted

From the manual:

 

A/C (Air Conditioning): Press to

turn the air conditioning system on

or off. An indicator light comes on to

show that the air conditioning is

enabled. If the fan is turned off, the

air conditioner will not run. The A/C

light will stay on even if the outside

temperatures are below freezing

 

ENABLED does not mean the compressor is running. The compressor still cycles.

I means it CAN run when the control thinks it is needed for humidity or temperature control.

gmissed Enthusiast

gmissed

Posted
Posted

. Set it for 21C it blows cool air set it for 22 it blows HOT in manual.

Agree wholeheartily with this. Nothing like the Ford I had, you could set it for 21.5 C and it would maintain that temp perfectly. I miss the Ford in that category.

tanner709 Enthusiast

tanner709

Posted
Posted

I was steady changing from 21-22 on the way to work this morning. It does seem to eventually balance out but it takes a long damn time...

 

Does the controller adjust blower temp based on the error of the cabin temps vs set point or does it just try to maintain an output of XX degrees from the blower at all times?

 

Might be the placement of the RTD in the cabin causing the issue.

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