I have a problem with the HVAC system.

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ID Status Date Year Make Model Transmission Type A/C Controls Public/Private
#13745 Closed 2004 GMC Siera 1500 SLT public

The passenger side blows hot when it’s hot outside and cold when it’s cold outside. Sometimes it will work correctly for a while then sometimes not. I have replaced both blend door actuators done the recalibrate procedure. I replaced the control module and did the recalibration which seems to work until you turn the truck off and start up again. Could I have a bad sensor?
My mechanic has scanned it with his scan tool (not a tech 2) He can read the move the blend door actuators and he gets no codes out of the HVAC system. The wiring diagram shows duct air sensors and this truck has the sun load sensor on the top of the dash. My mechanic also found a engine coolant sensor that seems to be reading -80 when the engine is hot he wants to replace that which I think is good but I doubt that could be causing only one side not to work correctly.
Would you think the air duct sensor could be bad for that side or maybe some other sensor for temperature? I am lost here as I am not sure where to find the problem.
Any words of wisdom would help.
Thanks,
Matt

During the re-caibrate procure you can fee the passenger side blow hot then to cold and then it reverts to warm even though the controls are calling for cold.
Sparky

Can you supply the part numbers of the installed actuators and their locations/positions?

Does your truck have manual or auto controls?

Which actuator is not working correctly?

The actuators were bought from Rock Auto part number SK604106. One was under the heater box the other was on top of the heater box the one that is a real pain to get at.
The truck is an SLT so it has the digital dual automatic controls. the passenger side is the one not working correctly. I did your re-calibrate procedure and you can feel both driver and passenger sides go to hot then cold and the drivers side stays cold the passengers side goes back to hot even though it’s 90 degrees here and the controls are set at 74 degrees.
Sparky

Will the driver’s side respond to full hot commands?

What happens when you set the temperatures to 60?

Yes the drivers side responds to full hot. when you turn the temps on bot sides to 60 the drivers goes to full cold and the passengers stays hot.
Sparky

Dis connect and reconnect the harness connectors behind the end cover at the passenger side of the dash. Inspect for any signs of corrosion on the metal terminals. Perform a recalibration and see what happens.

If that does not correct the issue try gently wiggling the connector at the passenger side temperature door actuator and see if it will start moving. Have the control panel set to full cold.

If nothing good happens there then we either have to get into detailed scan tool diagnostics or consider that the new actuator may be faulty.

The truck is at a mechanic and he has tried all of those things. The fully thing is that the new actuator does exactly what the old one was doing no change what so ever after installing the new one. When you put the system in learn mode it will run both sides to hot and then cold then the passengers side goes back to hot. Very strange.

I got the truck back from the mechanic yesterday and it’s still not working. They tried a new HVAC control and having the HVAC reflashed by another shop that had a Tech 2 scanner. Their thinking that I have a bad replacement actuator. The dash is still apart so last night I listened to the HVAC system with the engine off and the blower turned down to minimum and I can hear what I think is the new actuator making a buzzing sound like its trying to move and can’t. Today I am going to take the wiring plug out and see if the sound goes away. If it does I think I am going to have to remove the actuator and see what is going on.

Sparky

If you are going to remove the actuator try installing it in place of the driver’s actuator and see if the problem follows the actuator.

I will try that. I also want to make sure that the blend door turns by hand without binding. I did not try that when I had the actuator out.
Thanks for trying to help me out with this problem.

I pulled the actuator and installed it in the drivers side and it works fine. The blend door shaft moves easily from side to side with no binding. I did the re calibrate procedure with the actuator plugged back into it’s wiring connector but hanging out so I could see what was happening. When I do the recalibrate the actuator goes full hot then to full cold and stays there. I turn the truck off for 10 to 15 seconds and restart it. The actuator then moves to about the center. I try the controls and it will move to full hot when I move to 90 degrees. When I move to 60 degrees the actuator only moves back to a little passed center.
As I said before my mechanic installed a new HVAC control unit and had it re-flashed. Could this be a feedback problem? Or a control issue?
Sparky

The answer could be both. The only way to know is to look at codes and data so that one can decide on a diagnostic path.  Swapping the two actuators and keeping the problem at the same location at least should rule out a faulty actuator.  You also stated that you have full temperature control over the driver’s side so that rules out the outside and interior (ceiling mounted) temperature sensor.  I would want to take a quick look at desired versus actual vent (upper and lower) temperature readings and commanded versus actual actuator counts. There could also be separate sun load readings for the two sides.  Depending on how the data reads, I would then move on to either voltage tests of the various signals at multiple locations or perform loaded continuity tests of the wiring.

Never hurts to ask. Are you any where near the greater Charleston SC area?

It sounds lie I need to take it to a shop that has a tech 2 scanner. I live outside Boston Ma. I wish I was closer to your shop I would be making an appointment to see you!
I need to find someone in the local area that has the tools needed. I guess I may have to contact a GM dealer. What I did for the time being is run the calibration following your procedure and put the truck off when the passengers side went to full cold and pulled the plug out of the passenger side actuator so I get full cooling on that side now.When I find a shop that has the equipment I will plug the actuator back in and explain what is going on with the truck and give it to them to work on. That will be a while as I am out of work and don’t have a lot of money to put into the truck A/C right now.
Thanks for trying to help me out.
Sparky

Although I prefer the Tech 2 most times you just need to have a tool that has the same access as the Tech 2. I also use the Autel Maxisys and it works quite well for this job.

I was looking on line for a Tech 2 scanner thinking it might be less expensive than taking the truck into a dealer. I found this one http://www.obd2tool.com/goods-1568-GM+Tech2+GM+Scanner+-CANdi++TIS+(Works+for+GMSAABOPELSUZUKIISUZUHolden).html

Also I can buy a 1 year AC Delco subscription for software downloads for one VIN number for $40 I don’t know if almost spending $300 would be worth it over taking it to a shop that has the tools or dealer?
Sparky

That is a Chinese cloned tool and GM does not support it. Some people say they work and some people say they don’t. Nobody seems to trust them for programming.

I guess I won’t go that route! does the Autel do re-programming or do I need a real Tech 2 for that?
Sparky

The Autel Maxisys Pro model will but they are in the $2500 to $3500 range. The less expensive ones that you find are not USA supported.

I guess I will find a shop to take the truck to that has the right equipment.

WhenI was talking with my mechanic today he said that the counts for that actuator were all over the place. That is why he thought that the actuator was bad or that the HVAC control was bad. Do you know if anything else could cause the counts to be all over the place?
Sparky

Since you have proved out that the actuator itself is good then there is a poor connection somewhere. The most likely will be at the actuator connector itself. When I am tracking down such a problem I monitor the counts on the scan tool while manipulating harness connectors.  That way I can see if harness movement can induce erratic readings or stabilize it if it is already erratic. The three likely spots for trouble are at the actuator connector, the connectors at the passenger end of the dash or at the HVAC control.

2006 Chevrolet Silverado-Driver’s Temperature Door Erratic

Okay thanks I will check those connectors.

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