Another HVAC POST

[zmusclow]

So I have been searching and have not found this issue. I have a 2002 Tahoe with automatic AC controls. I replaced the mode door actuator and it was working, but would not fully go to defrost or the upper setting (would be always blowing some out of the feet vent). I just tried to do the actuator calibration. I pulled the fuse for 3 min, reinstalled the fuse and turned key on for 2 min, key off for 15 seconds and key on to test. Now my mode door actuator is stuck on full defrost no matter what setting I have it on. It appears that the actuator went past the range marks while it was installed. Am I doing the calibration wrong or is a Tech 2 needed for a proper calibration?


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[UmmScott]

So I have been searching and have not found this issue. I have a 2002 Tahoe with automatic AC controls. I replaced the mode door actuator and it was working, but would not fully go to defrost or the upper setting (would be always blowing some out of the feet vent). I just tried to do the actuator calibration. I pulled the fuse for 3 min, reinstalled the fuse and turned key on for 2 min, key off for 15 seconds and key on to test. Now my mode door actuator is stuck on full defrost no matter what setting I have it on. It appears that the actuator went past the range marks while it was installed. Am I doing the calibration wrong or is a Tech 2 needed for a proper calibration?


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What kind of actuator did you install?

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[zmusclow]

What kind of actuator did you install?

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I installed the AC delco replacement. I also manually reset the actuator by taking the cover off and rotating the motor. When I retried the calibration it just defaulted to full defrost again.


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[UmmScott]

I installed the AC delco replacement. I also manually reset the actuator by taking the cover off and rotating the motor. When I retried the calibration it just defaulted to full defrost again.


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Sounds like there's something wrong with the control head.

When the control heads go bad they make the actuators do weird things.
In my 00 yukon the control head kept cycling the recirculation actuator from open to closed repeatedly with no reason.
Replaced control head and issue went away

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[zmusclow]

Sounds like there's something wrong with the control head.

When the control heads go bad they make the actuators do weird things.
In my 00 yukon the control head kept cycling the recirculation actuator from open to closed repeatedly with no reason.
Replaced control head and issue went away

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Thank you for the info. Junkyard shopping it is


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[Fless]

There can be updated calibrations (firmware) for the HVAC controls for improvement. Can be done using a Tech 2 and TIS2000.

 

[zmusclow]

Update: I got a Tech 2 hooked up to the Tahoe today. I am getting DTC B0248 “Air Flow Control 3 Circuit”, and B3761 “Air Flow Control 3 Feedback Circuit”. It has a brand new AC Delco Mode door actuator. The actuator moves on command from the Tech 2, but on the data screen it shows mode door max and min position as zero. I don’t know if it’s a bad actuator or if the head unit is bad. Any and all input would be appreciated.

Also upon key off and key on after disconnecting ring the tech 2, the mode door actuator defaults back to full defrost


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[UmmScott]

Control head is bad..

Replace control head, problem goes away [emoji106][emoji106]

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[zmusclow]

Control head is bad..

Replace control head, problem goes away [emoji106][emoji106]

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Thank you! I just ordered one


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[UmmScott]

Unless you have an odd ground or wiring issue, I'd definitely replace the control head

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[zmusclow]

Just replaced the control head. I am having the same issue with both of the control circuit 3 fault codes[emoji24]. I am at a loss of where else to troubleshoot are there any other things it could be? Maybe a bad actuator? When commanded from the tech 2 the actuator still moves full range. When looking at the tech 2, the commanded position is always on 0 unless commanded by the scanner and the min and max counts are 0. Just on the mode door actuator.


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[zmusclow]

Update: has to replace mode door actuator again and problem is solved.


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[tRidiot]

Update: has to replace mode door actuator again and problem is solved.


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What parts did you use for the initial and now subsequent replacement? OEM or aftermarket or what?

 

[afpj]

thought I’d pile on and share my troubleshooting without a tech2:

2002 Yukon 5.3 4x4 213k miles. One day it would only blow at footwell and defrost vents. Couldn’t manually even select primary vents ( to your face). found b3761 code. Got gm mode control actuator installed (pita), can see it cycle the same as the original (would only move from foot to defrost or both, but no primary vent selectable). Unplugged battery to do a total reset. This resulted in default defrost only mode. Recirc also now doesn’t work. . Got to be the controller, so Start looking for hvac control unit. Can only find dorman. Even Chevy dealer doesn’t have it ( no longer made). Not fond of dorman, but had no choice. Got a reman unit part 599-260, but didn’t work (specs says needs programming, thought it meant recalibration, but apparently not). Paid more and got a new unit dorman part 599-215. Works. All modes work correctly. Only issue is erratic temps ( large hysteresis effect) . Thought maybe it was the unit I got, so exchanged for another, same issue. Well, guess I just have to adjust the temp differently from Oem, but at least all modes work. Not exact replacement as per dorman advertisement
, but no choice.

yeah, could’ve saved money on the mode controller with a tech 2, but with my luck, getting something that can only be used on gm cars essentially guarantees something cataclysmic would happen to the Yukon. YMMV.

 

[afpj]

Thought I’d update this regarding the dorman hvac controller. I’m on my 3rd unit. Second unit was better than the first with regards to temp control, but second unit would not turn on ac after turning off the car and everything set to auto. Had to turn off then turn on using the ac button, and ac would kick on. Well traded that in for 3rd unit. Worked for about a week like it’s supposed to, now it doesn’t turn on the ac after engine restart despite the ac light being on, have to turn off then turn back on like the 2nd unit. Dorman strikes again. I thought if using eBay for a used unit, but with my luck it would be bad and screwed again. Well, I’m hoping it’s not my bcm.

 

[tRidiot]

Jeez, what a nightmare. I don't understand how Dorman stuff is so SH***Y. And how they haven't been sued out of business.

 

[Chad98]

Anyone figure out the control head issue? I have a 2002 Tahoe that’s stuck on defrost. I’ve replaced ALL the actuators with new AC delco units. No change...I replaced the control head with a used one..no change. Tried a Dorman Remanufactured unit part # 599-260 for vehicles with rear ac since mine has it...no change. So I try a new Dorman unit part number 599-215 and full functionality is restored...until I discovered now my rear ac is not working at all because this control head is for vehicles without rear ac...this tells me that the front controller and rear controller MUST be able to communicate with each other. Tried putting the correct control head back in and it again defaults to defrost and will not move. I’ve tried every recalibrate procedure known and no change. Seriously thinking about just using the incorrect control head just so I’ll have full front functions but I REALLY want both front and rear to work as designed. Anyone have any idea on WHY it defaults to defrost with the correct control head, but functions fine when the incorrect control head is installed? (I just lose rear air)

 

[swathdiver]

Y'all could have bought a Tech-2 and moved on to greater pursuits. It would have paid for itself already too.

Dorman parts in this area are so inferior you are better off with used from the salvage yard.

 

[S33k3r]

Anyone figure out the control head issue? I have a 2002 Tahoe that’s stuck on defrost. I’ve replaced ALL the actuators with new AC delco units. No change...I replaced the control head with a used one..no change. Tried a Dorman Remanufactured unit part # 599-260 for vehicles with rear ac since mine has it...no change. So I try a new Dorman unit part number 599-215 and full functionality is restored...until I discovered now my rear ac is not working at all because this control head is for vehicles without rear ac...this tells me that the front controller and rear controller MUST be able to communicate with each other. Tried putting the correct control head back in and it again defaults to defrost and will not move. I’ve tried every recalibrate procedure known and no change. Seriously thinking about just using the incorrect control head just so I’ll have full front functions but I REALLY want both front and rear to work as designed. Anyone have any idea on WHY it defaults to defrost with the correct control head, but functions fine when the incorrect control head is installed? (I just lose rear air)

Sounds like you have a wiring issue between the head unit and the rear AC. This is suggested because it works fine if you take the rear out of the mix, but misbehaves when the rear is included.

 

[Fjs0001]

Anyone figure out the control head issue? I have a 2002 Tahoe that’s stuck on defrost. I’ve replaced ALL the actuators with new AC delco units. No change...I replaced the control head with a used one..no change. Tried a Dorman Remanufactured unit part # 599-260 for vehicles with rear ac since mine has it...no change. So I try a new Dorman unit part number 599-215 and full functionality is restored...until I discovered now my rear ac is not working at all because this control head is for vehicles without rear ac...this tells me that the front controller and rear controller MUST be able to communicate with each other. Tried putting the correct control head back in and it again defaults to defrost and will not move. I’ve tried every recalibrate procedure known and no change. Seriously thinking about just using the incorrect control head just so I’ll have full front functions but I REALLY want both front and rear to work as designed. Anyone have any idea on WHY it defaults to defrost with the correct control head, but functions fine when the incorrect control head is installed? (I just lose rear air)

Have you had any luck?

I've been having similar issues for about 3 years. I have to unplug the actuators while they recalibrate so they stay on the cold or hot setting. This isn't my daily unless my other cars are down. I've been waiting on something else to go wrong to justify buying a tech2.