I have searched a lot on these topics but cant quite locate what I am looking for or maybe I am just over looking the correct thread.

My first issue is my DIC displays "ice possible" when the temp on the mirror shows to be over 60 degrees. Not a huge issue but there is obviously a problem. My suburban does this but when it is actually very cold out and the compass will read "ICE" but the hummer will not display that it actually shows pretty close to the temp that is outside.I have replaced both temp sensors located under the hood. This issue will also prevent the AC from coming on because something is telling the truck it is cold outside. Like the temp on the compass will read 64 but the " ice possible" message will display on the dash . Even sometimes it will be well over 90 degrees or even over 100 and the AC wont come on, it blows the air but when you hit the snowflake button the little amber light on it just flashes. It literally just works when it wants to and in this Texas heat I can't have that in an all black SUV. Which brings me to my second issue. I assumed the HVAC system was the same on my suburban as the H2 so when I realized this AC gets no where as cold as the suburban I assumed there was an issue. It will not cool the truck off by any means even after driving for an hour. Also there is no air coming out of the center console vents for the rear. I have tried resting the HVAC system, I pulled the fused wait awhile then turned the key on but did not start it, I could head all the actuators moving around and it defaulted the temp at 74 degrees so I assumed the system actually rested.

I have read forums for awhile now and noticed people are always posting things in the wrong section, I hope I have not done this and I apologize if I have. Also thank you to anyone who can provide any help on these issues.

 

there are some plugs with blue caps on your bumper when you open your hood near the headlights. they look like they are extra capped off plugs for some type of light accessories but they are supposedly ambient air temp sensor's maybe check them or swap them around to see if the error also moves with them.
they look like this

 

Yes, I mentioned above that I replaced both of those. I guess I could replace them both again, maybe I just got some bad ones.

 

Not sure if the outside temperature influences the HVAC system. Anyway it sounds like an AC pressure issue, possible a leak. Pressing the SnowFlake button engages the clutch (on the compressor) with the drive belt. If pressure doesn't build-up the clutch will automatically be disengaged and the lamp will go off.

Check the pressure-switch on the dryer, make sure its connected (easy to see, could be faulty) Check the clutch engages when you press the button (should be able to hear) Check the clutch connector located close to the compressor.

Otherwise there could be a range of issues from a leak, faulty clutch, faulty compresser etc. Take the truck to have the A/C pressures checked, the guys there should be able to help.

Only the right amount of refrigerant is used, over filling or underfilling can cause issues (Should be 1.6lbs of R134a) , my local garage damaged my compresser by overfilling, so I had to replace it and several other components.

Feel free to ask for more details and please keep us posted.

 

Well if it is super cold out the truck wont let the AC comp come on, or at least that is how my 03 suburban works. So that is what makes me think it is related to that since the DIC is saying "ice possible" even if its 100 degrees outside. I am not sure if there is another sensor somewhere that is independent from the two next to the bumper.


I also did that as well, I had a shop put gauges on it and they said everything was fine. I did not personally see the reading, I am going to my granddads next week and I am going to have him check it with his set of gauges.

My granddad also said the pressure switch might be faulty or maybe the orifice tube is bad, but there isn't a way to check those unless I want to lose all of my freon. The compressor does kick on and off and under a load like it is suppose to, when I put my foot into it you can really tell when it kicks off because it gets really ho. It blows cold air, just not cold enough or maybe the air is mixing with the hot somewhere, I did have an actuator issue but I got that fixed so I don't think it is related to that.

 

There are also two temp sensors in the ductwork in the dash and one over your head behind the microphone in the other tiny grille on the ceiling.... Does not seem like those would be the one the DIC message is based on but maybe one is. The two by the pass headlight are the HVAC and mirror ambient temp sensors. One in the headliner is the inside air temp sensor and the two in the ducts are for left and right temp sensing. So my only other guess would be the one in the headliner.

It just seems highly unlikely to me though. My guess - wiring fault. The temperature sensors are resistance based. The temperature changes the resistance. If there is a connector either right at the sensor, inline harness connector, or at the BCM that the pin in the connector is come loose this could very much be the cause. You could rule out the sensor itself by just swapping the two of them. If one is bad than you would get a bad temp reading on the mirror instead of ice possible on the DIC. The ice possible message is a class 2 bus message sent from the BCM to the DIC in the instrument cluster. That same sensor also is used for the AC when in its "automatic mode". So that might also be a clue in that the temps in the automatic mode will also get wonky as it uses data from that same sensor, the sun load sensor on the dash, as well as the inside temp sensor to determine the correct settings in the auto mode.

 

After a bit of research you are correct, when the HVAC ambient air temerature is below 40F the HVAC doesnt come on. It gets pretty cold here but I've never noticed the A/C symbol, even when my A/C failed the symbol stayed on.

The attached PDF describes the Hummer HVAC operation, its worth reading!

There is also a which relates to a similar problem to yours.

Based on bonxteck's diagram and MixManSC's comments, plus the PDF, I'd be tempted to re-check the two thermisters, as their resistance decreases with temperature, an Open-Circuit will be interpreted as the lowest possible temperature.

According to the PDF if you pull out the two sensors shown in bonxteck's diagram (think 3 is the HVAC, 5 is the Mirror), you sould be able measure around 5V accross the pins of each connector, if there's no voltage then there's a fault (I'd be tempted not to use any oil-based cleaner in the connectors)


If I get time today I'll see if I can replicate your problem.

Also see the attached wiring diagram, search for ambient air temperature to find the relevant information.

 

Just checked my H2.

Both thermisters measure 18.4K Ohms at 54F (12C)

When unplugged, each connectors read 4.9V, interstingly the Mirror connector has +ve on the left, the HVAC connector has +ve on the right (which might help identify it) as my wiring is quite not like that shown in the physical diagram.

Removing the HVAC thermister had no effect on the A/C symbol also I didn't get the "Ice Possible" warning, though perhaps I should have waited longer.

Strangely when the Mirror sensor was unplugged the Mirror read -10C (not F) when reconnected it wnet to 4C and now seems stuck there. I'll recheck later.

Still stuck now I might have a problem too!

Oh just rechecked and its gone up to 6C, must be a really long averaging period (HVAC period might be similar which may explain things)

Update now back to normal.

 

Thank you all for those replies I will check mine later today when I get home. Today I noticed it wasn't cooling the cabin down as much as it normally does so I looked down and the recirculation light wasn't on so I hit the button and it just blinked a few times and wouldn't come on. At this point there definitely has to be a problem with wiring somewhere I am almost tempted to just take it to the dealer but I can see the money signs already.

 

The recirc will only function in certain modes and under certain conditions. You cannot make that come on in certain modes and conditions so that is not usually an error or fault...