02 LB7 CCSB HVAC Control Panel Issues

Bdsankey

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So on drive to/from DPC 2019 I was experiencing some HVAC issues. All of a sudden while driving the A/C would just stop like it would try to switch vent positions (position wasn't touched on the control panel). You could hear air moving inside the dash (fan was loud) but not much came out of the vents even on max fan speed. We unplugged the mode control door actuator on the driver's side of the ducting thinking that somehow it was moving and causing an issue. That didn't fix the problem.





I am wondering if my HVAC control panel is acting up and just doing what it wants? It fixes itself at every single key cycle, for example if you pull over or stop for fuel and shut the truck off it will work properly for some time. Also, if you turn the HVAC off for say 30-60min and then turn it back on sometimes it works correctly sometimes it doesn't. The only sure fire fix is a key cycle.
 

zakkb787

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I believe there are three different actuators under the dash. My dads 99 would do weird things and of course it was the hardest to get to. Might could find a cheap panel on eBay to double check, but my bet would be on one of the actuators.
 

Bdsankey

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I believe there are three different actuators under the dash. My dads 99 would do weird things and of course it was the hardest to get to. Might could find a cheap panel on eBay to double check, but my bet would be on one of the actuators.
The actuator must be told what to do is the part that boggles my mind. If it isn't being told to move it *shouldn't* move.
 

JoshH

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Is this while running the A/C only? I had an issue with my LMM when I swapped the control module, and it was programmed for an evap temp sensor instead of a low pressure switch. It wouldn't allow the compressor to cycle and the evaporator core would freeze up and act like you are describing. It would make a lot of noise, but no air would come out any of the vents. I would have to turn of the truck or A/C for a little while and let the evaporator thaw out so air could flow through it. I figured it out when I popped the hood and saw a half an inch of ice on the low pressure line running to the compressor coming out of the dryer/accumulator.
 

Bdsankey

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Is this while running the A/C only? I had an issue with my LMM when I swapped the control module, and it was programmed for an evap temp sensor instead of a low pressure switch. It wouldn't allow the compressor to cycle and the evaporator core would freeze up and act like you are describing. It would make a lot of noise, but no air would come out any of the vents. I would have to turn of the truck or A/C for a little while and let the evaporator thaw out so air could flow through it. I figured it out when I popped the hood and saw a half an inch of ice on the low pressure line running to the compressor coming out of the dryer/accumulator.
I believe only while the A/C is running. I haven't had that level of buildup but it also is random lengths of time. Sometimes its hours, others its a few minutes which is why I'm leaning towards a dumb electrical control issue vs a freezing evap core. I guess next time it does it I can pull the cabin air filters and look at the core.



It's got a brand new ACDelco compressor, new ACDelco receiver/drier, new ACDelco orifice tube, new ACDelco pressure switches, new off brand hoses/lines. Only part of the system not new is the evap core. It could be an evap core, I just pray to god it isn't. If I recall correctly it requires me to gut the dash to change.
 
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BlkMax

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Can you override control of that system with a Tech II?


I know I can do it on my '04, but that one has the fancy side to side, automatic HVAC controller in the dash...
 

DAVe3283

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The blend door motors have been the same since the mid-1990s on GM vehicles, and they are kind of a crappy design. It is a crappy little DC motor run through 3 sets of plastic (yes, plastic) gears to drive the output. Off one of the gears is another gear to a rotary potentiometer.

There are a few ways they fail. Older ones would crack the output socket, so the actuator would move but the blend door wouldn't. Later ones use a metal insert in the final gear to help with this. Or one of the other gears can crack, strip teeth off, etc. Then it won't be able to move where it wants, and can sometimes change temperature as a bump in the road moves the blend door and the actuator can't do anything about it. Or it just gets stuck at some position until a bump moves it past the broken teeth. Finally, the potentiometer can get worn/dirty and think the actuator is positioned somewhere it isn't. This will cause the control module to command the actuator to move towards the "correct" spot (which, of course, isn't).

If the control module commands the actuator to move (+) and sees the feedback decrease instead (due to flaky pot), it will disable the actuator for that key cycle. This sounds like what yours is doing. So if the foot/face/defrost (mode door) actuator pot flakes out, the control module will attempt to put it "back" (even though it never moved, it thinks perhaps you hit a bump, but it's just crapped out). Now it starts moving, and might suddenly report travel the wrong way (again, crappy sensor, not actually doing the wrong thing). Module freaks out, gives up, and disables that actuator, now helpfully located in some useless in-between mode sending air half to your feet half to windshield or some crap.

None of the actuators are easy to get to. The pre-03 trucks are subtly different, but on my 2003 I had to remove the dash trim entirely (which means passenger air bag, vents, etc. come off) to get to the actuators. Then the replacement BRAND NEW ACDELCO mode actuator didn't have the balls to actually change modes, and would get stuck if I tried to use defrost, so I ended up DOING IT ALL AGAIN to put the original back, since that one worked besides some random clicking noises. But I'm not bitter, no sir...


Anyway, good luck / have fun. I wish I could tell you a brand of actuator to replace them with to never have to touch them again, but as far as I can tell, they are all crap, so just get whatever is cheapest and cross your fingers.
 

Bdsankey

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Can you override control of that system with a Tech II?


I know I can do it on my '04, but that one has the fancy side to side, automatic HVAC controller in the dash...
I believe a tech2/snapon will command them. I know it works on my 99 bonneville. That’s going to be my first step before just throwing parts at it.
 

Bdsankey

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The blend door motors have been the same since the mid-1990s on GM vehicles, and they are kind of a crappy design. It is a crappy little DC motor run through 3 sets of plastic (yes, plastic) gears to drive the output. Off one of the gears is another gear to a rotary potentiometer.

There are a few ways they fail. Older ones would crack the output socket, so the actuator would move but the blend door wouldn't. Later ones use a metal insert in the final gear to help with this. Or one of the other gears can crack, strip teeth off, etc. Then it won't be able to move where it wants, and can sometimes change temperature as a bump in the road moves the blend door and the actuator can't do anything about it. Or it just gets stuck at some position until a bump moves it past the broken teeth. Finally, the potentiometer can get worn/dirty and think the actuator is positioned somewhere it isn't. This will cause the control module to command the actuator to move towards the "correct" spot (which, of course, isn't).

If the control module commands the actuator to move (+) and sees the feedback decrease instead (due to flaky pot), it will disable the actuator for that key cycle. This sounds like what yours is doing. So if the foot/face/defrost (mode door) actuator pot flakes out, the control module will attempt to put it "back" (even though it never moved, it thinks perhaps you hit a bump, but it's just crapped out). Now it starts moving, and might suddenly report travel the wrong way (again, crappy sensor, not actually doing the wrong thing). Module freaks out, gives up, and disables that actuator, now helpfully located in some useless in-between mode sending air half to your feet half to windshield or some crap.

None of the actuators are easy to get to. The pre-03 trucks are subtly different, but on my 2003 I had to remove the dash trim entirely (which means passenger air bag, vents, etc. come off) to get to the actuators. Then the replacement BRAND NEW ACDELCO mode actuator didn't have the balls to actually change modes, and would get stuck if I tried to use defrost, so I ended up DOING IT ALL AGAIN to put the original back, since that one worked besides some random clicking noises. But I'm not bitter, no sir...


Anyway, good luck / have fun. I wish I could tell you a brand of actuator to replace them with to never have to touch them again, but as far as I can tell, they are all crap, so just get whatever is cheapest and cross your fingers.
Thanks for the info. It’s like it just randomly loses the ability to move air even with the mode door unplugged which leads me to a recirc door issue or control issue. If I can command it to do what I want via a tech2/snapon to me that would point towards a heater panel.



I don’t believe the 2002 trucks have a cabin sensor that it used to read off of. Mine just has the hot/cold dial without any temp numbers on it.
 

JoshH

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It has been a little while since I tore into the HVAC housing, but the best I can remember, there is no way for the actuator to move and completely block flow through the vents. It will either come out the floor, dash, or defrost in some combination.
 

Bdsankey

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It has been a little while since I tore into the HVAC housing, but the best I can remember, there is no way for the actuator to move and completely block flow through the vents. It will either come out the floor, dash, or defrost in some combination.
I should be more specific, it doesn't 100% block flow. There is very very very little airflow out the upper vents, less coming out the floor, and even less out of defrost.
 

JoshH

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There is only one actuator that moves the doors to divert air through all three outlets. It is impossible to have dash vents and defrost vents open at the same time because of how it is configured. The air flow you're feeling out of the floor and defrost are probably just leakage around the doors. I still think you have something blocking airflow. If it isn't the evap core freezing up, then there must be something in there covering it. I would hook up some A/C gauges and watch pressures to verify proper compressor cycling.
 

Bdsankey

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There is only one actuator that moves the doors to divert air through all three outlets. It is impossible to have dash vents and defrost vents open at the same time because of how it is configured. The air flow you're feeling out of the floor and defrost are probably just leakage around the doors. I still think you have something blocking airflow. If it isn't the evap core freezing up, then there must be something in there covering it. I would hook up some A/C gauges and watch pressures to verify proper compressor cycling.
That I have done, compressor cycling is correct. I don't recall exactly what PSI but it was within spec according to Mitchell1 as I checked that before we left (8hrs before we left and freon hadn't been added since the refill after changing a fitting).






Guess its time for the dash to come apart to change all the actuators/evap core/heater core/clean the box.
 

DAVe3283

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You should be able to see the evaporator through the cabin air filter door. Maybe let it get in the weird no-flow state, then pop the filters out and look at the evaporator to see if it is iced up? On my 2003 with the retrofit filters, if I open that door with the fan on, a metric crap-ton of air comes out the opening as it is easier than forcing through the evaporator and ducting.

It will tell you a lot either way. If you get air out the air filter door, the fan is working fine, and something downstream (ice?) is blocking it. If you don't get much out the air filter door, something is restricting the fan. You can pull the fan pretty easily and see what's up.
 

Bdsankey

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You should be able to see the evaporator through the cabin air filter door. Maybe let it get in the weird no-flow state, then pop the filters out and look at the evaporator to see if it is iced up? On my 2003 with the retrofit filters, if I open that door with the fan on, a metric crap-ton of air comes out the opening as it is easier than forcing through the evaporator and ducting.

It will tell you a lot either way. If you get air out the air filter door, the fan is working fine, and something downstream (ice?) is blocking it. If you don't get much out the air filter door, something is restricting the fan. You can pull the fan pretty easily and see what's up.
That is the plan sir! Just gotta wait till it's doing it AND I get home. I'm going to bring my tools with me OR just remove the plastic decorative cover over the fan/box/filters.
 

Chevy1925

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My truck will ice up the evap come high humidity during the summer if i leave it on blower setting 1 or 2 for a while. when i realize im not getting much air on my face, ill click the a/c off and slowly you feel the air start coming back. Once the air starts to blow a bit warm, click the a/c back on and off we go for another 30-40 min before it ices up again. takes about 5-10 min to melt off and back to blowing good but if you are leaving the a/c on the whole time, its just freezing up more and more no matter where you turn the dials

we dont have thermistors in the evap to cycle the compressor off so icing up can be frequent if you have a higher flowing orifice tube in place (higher super heat, or lower or something like that, it just flows more refridgerant through it). Good for hot hot temps but not when things cool down and humditiy is high.
 

Bdsankey

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My truck will ice up the evap come high humidity during the summer if i leave it on blower setting 1 or 2 for a while. when i realize im not getting much air on my face, ill click the a/c off and slowly you feel the air start coming back. Once the air starts to blow a bit warm, click the a/c back on and off we go for another 30-40 min before it ices up again. takes about 5-10 min to melt off and back to blowing good but if you are leaving the a/c on the whole time, its just freezing up more and more no matter where you turn the dials

we dont have thermistors in the evap to cycle the compressor off so icing up can be frequent if you have a higher flowing orifice tube in place (higher super heat, or lower or something like that, it just flows more refridgerant through it). Good for hot hot temps but not when things cool down and humditiy is high.

Humidity was decently high during parts of the drive. Here it has been humid. It’s a standard GM orifice tube, not the nuclear climate ones.
 

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