HVAC Control Head?

[drdave81]

Just want to make sure I'm not missing anything here. My HVAC only blows out of the dash vents. When I actuate the mode door with a Tech2, I can get it to sweep from the dash, to the floor, defrost, and back. So I know the actuator works. Seems like the control head would be the issue. I've also done the recalibration procedure, with no change. It always stays on the dash after the Tech2 runs the actuator sweep. Is this a common issue, or am I missing something else?

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

@swathdiver may be able to give you some insight and/or guidance in troubleshooting this issue with the Tech 2.

 

[Doubeleive]

Just want to make sure I'm not missing anything here. My HVAC only blows out of the dash vents. When I actuate the mode door with a Tech2, I can get it to sweep from the dash, to the floor, defrost, and back. So I know the actuator works. Seems like the control head would be the issue. I've also done the recalibration procedure, with no change. It always stays on the dash after the Tech2 runs the actuator sweep. Is this a common issue, or am I missing something else?

if you are not getting any feedback bcm codes from a actuator, then you could try reprogramming the control head or just replace it. the fee is $40 per vin code for 2 years of programming for unlimited programming on that vin. you will need a pc/laptop and a serial port and the cable for the tech2

 

[drdave81]

Sorry, was on vacation for a few days. I'm not getting any DTCs. The fan control and temp both work fine, just the mode knob. Running the actuator via Tech2, it will move, so I know it's not the actuator. Just need to find one in good shape like mine is. Off to a junk yard today, assuming rain holds off.

Doubelieve, you mention reprogramming. Are you referring to a flash update for the control head? I wasn't aware these were flashable. Or am I misunderstanding what you mean.

 

[drdave81]

Another control head in, does the exact same thing. Actuate the mode door with Tech2, and it sweeps between all 3 levels. Stop the actuator and it goes right back to blowing out of the vents regardless of what the controls are set to.

 

[Doubeleive]

where did you get the one you put in it now? if it is used did it come out of the same style truck or did you just get one that looked the same?
depending on the year and style then yes you can put a new calibration on it with the tech2 and using acdelco tds web, they charge $40 for 2 years of unlimited programming per vin number.
have you scanned the hvac system for any dtc's? with the tech2 it should also tell you if the commanded state does not match actual state, being it is a nbs it might not give all the data it does on a nnbs though.
also if you have previously replaced any actuators if you used the wrong one this problem will occur because even if the actuator looks the same and fits the same it won't work the same it will do exactly what is happening now. has it always done this? or is this a problem that just happened since you owned it?

 

[drdave81]

where did you get the one you put in it now? if it is used did it come out of the same style truck or did you just get one that looked the same?
depending on the year and style then yes you can put a new calibration on it with the tech2 and using acdelco tds web, they charge $40 for 2 years of unlimited programming per vin number.
have you scanned the hvac system for any dtc's? with the tech2 it should also tell you if the commanded state does not match actual state, being it is a nbs it might not give all the data it does on a nnbs though.
also if you have previously replaced any actuators if you used the wrong one this problem will occur because even if the actuator looks the same and fits the same it won't work the same it will do exactly what is happening now. has it always done this? or is this a problem that just happened since you owned it?

- The one I got was a used one out of an 02 Yukon, same part number as the old one.
- Earlier, the only code I had was U1500 - Inter Device Dedicated Bus Malfunction. Checking again after playing around with the tool now sets B0248 - Air Flow Control 3 Circuit.
- I haven't replaced any actuators because it works when the tool commands it. I have only owned the vehicle for a week, it was one of the things I noticed when I purchased it. The seller gave me the "hmmm, guess I hadn't noticed that before". Trying the recalibration in the tool and pulling the fuse for 15 seconds, then letting it run for 45 seconds didn't fix the issue either.

Checking the commanded and actual states were pretty close on defrost and floor, within a couple of counts, yet it stayed on vents. When commanded to the vents, the commanded counts went to 0 while actual stayed at 67. This would lead me to think that the actuator is moving, while not moving the mode door, yet when the tool commands it to move, then it actually will push air out of the defrost/floor. That would make me think it works.

I may try a used actuator, since the junk yard has a 1 year warranty on all the parts, so if it doesn't work I can just return it. Try to rule out something else.

 

[Doubeleive]

- The one I got was a used one out of an 02 Yukon, same part number as the old one.
- Earlier, the only code I had was U1500 - Inter Device Dedicated Bus Malfunction. Checking again after playing around with the tool now sets B0248 - Air Flow Control 3 Circuit.
- I haven't replaced any actuators because it works when the tool commands it. I have only owned the vehicle for a week, it was one of the things I noticed when I purchased it. The seller gave me the "hmmm, guess I hadn't noticed that before". Trying the recalibration in the tool and pulling the fuse for 15 seconds, then letting it run for 45 seconds didn't fix the issue either.

Checking the commanded and actual states were pretty close on defrost and floor, within a couple of counts, yet it stayed on vents. When commanded to the vents, the commanded counts went to 0 while actual stayed at 67. This would lead me to think that the actuator is moving, while not moving the mode door, yet when the tool commands it to move, then it actually will push air out of the defrost/floor. That would make me think it works.

I may try a used actuator, since the junk yard has a 1 year warranty on all the parts, so if it doesn't work I can just return it. Try to rule out something else.

That air flow control circuit 3 is your clue, the actuators can go bad it may work when command with the tech2 but then goes back to doing whatever it wants and the tech2 see's it is not working right, it's a smart yet dumb system it can only point you so far.
B0248 Possible Causes · Faulty Mode Actuator
I am willing to bet once you get a working actuator in there then it will be fine.

 

[drdave81]

I'll try that and let you know. Too many threads go without any follow up on a fix. Thanks for the input.

 

[Fjs0001]

I have a similar issue. My blend doors are always stuck on hot. After I replace the fuse to recalibrate, they shift to allow cold air and then move back to hot. I hope you have success, please follow up.