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hyperv6, thanks for sharing the above information. It's good to see that GM finally came out with a TSB on this issue. The "negative effects on cabin comfort" listed in TSB #19-NA-177 are already happening with my truck. It is the least comfortable AC I've ever experienced, so I don't have much to lose in having them reprogram the control module. It may be several days before I can take it in, but I will update here afterwards.
 

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I'm glad that GM has issued this notice. I hope that it works okay for you. From what I've read, the temperature swings will be most prominent when the outside and inside temps are similar. So, in the heat of the summer, you may not notice much negative effects.

It would be interesting to know exactly what they are doing with this re-calibration. Raising the lower temperature limit to avoid "overshooting" ? Cutting back further and earlier on compressor volume output when they are close to a freeze up condition?? Or actually "de-clutching" the compressor at times (normally the compressor is running continuously and only de-clutches when it senses that temperature/pressure conditions could damage the compressor).

Please come back and report on your post re-calibration results. I'm hoping that you have positive results.
 

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So your truck is also a 2016. Has this been happening since new, or since you have had the truck? What action (if any) has the dealer taken? Where are you at now with GM and a resolution? I’m curious about what others with this a/c problem are doing for a fix. Thank you.
I got it used with 18k on it. And the AC issue has been there since the day I got it.
I’ve had it to the dealer 2 times. First time the cabin filter was pretty dirty and they replaced it saying that would fix the problem. Second time, they stated they couldn’t reproduce the problem but found the refrigerant was low so the evacuated and refilled. Haven’t been back a third time yet.


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I guess I must have been under a rock for the last few years but until the post above I hadn't known of the existence and function of the active grill shutters. Given that they are closed at startup and at highway speeds, I think it is highly likely they are contributing to the problems I'm having with the A/C temps rising on long highway drives, and fluctuating wildly at other times, particularly on hot days when I first start the car. I can see the failure to cool the condenser causing the system to trip the high pressure cutout, making the system shut off intermittently.
 

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It's the ones for the radiator in the grill. What I'm getting sounds like a different thing. My temp simply goes up a little rather than full loss of cooling.

Gotcha, different problem. Mine is simply a heat exchange problem but it does randomly do what you describe as well.

To me it sounds like a low side pressure problem rather than a fault. I know the r1234 system is different than 134a but the low side pressure switch should be kicking off the compressor once the condenser gets too cold, unless this is different. Once you're below 20 or psi your evaporator core should be around the same temp, meaning your pressure should be coming back up because the compressor is commanded off. On my old truck the cycle delay was such that the average low side pressure was around 28 psi which resulted in 38 degrees of vent temp and roughly 30 at the condenser. I would occasionally get freeze ups but usually changing the air filter fixed that. My problem was that the lowest fan speed was too low with a partially blocked filter.
Yes, this is different. As long as you have the climate control in either A/C or defrost, the clutch is in. On older vehicles the compressor would de-clutch periodically to keep the temperature stable. But on the 2017 and newer Colorado they use a variable displacement pump. So, when the cabin temp gets cool enough if "de-strokes" the compressor, reducing it's output volume. Not to zero though - - just reduces it. If the AC is starting to freeze up, I suspect that even de-stroking the compressor may not stop the "cascade" of freezing.

I've had dozens of freeze-ups. It starts slowly. Eventually the evaporator is largely frozen up and the blower output drops way down. If I stopped, I would find the IHX (integrated heat exchanger) tube white with ice. The IHX is a secondary stage in the AC. The output from the evaporator super-cools the incoming (warm) refrigerant so it can get even cooler when it goes through the expansion valve. In addition, the warm fluid heats up the low-pressure gases from the evaporator. Because the high pressure gases going into the radiator/heat exchanger are hotter, the system is more efficient in removing heat from the system. That is great for cooling - - but only if the system is kept under control. When it gets into a runaway condition, it accellerates the problem
 

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Brogers, Appreciate the info and I'll post in several weeks to about the "tweek" aka software upgrade.
Stan Irish, I sold my 2017 Colorado back to GM today at Quality Chev. Because I had experienced the problem early on (only 4K mile), they deducted very little mileage charge on the buy back.
The service mgr mentioned that he had changed the firmware on another Colorado 2 weeks ago and was waiting to hear how it worked. I'm guessing that the person he was referring to was you. So I presume that it has worked well for you?
 

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Yes, this is different. As long as you have the climate control in either A/C or defrost, the clutch is in. On older vehicles the compressor would de-clutch periodically to keep the temperature stable. But on the 2017 and newer Colorado they use a variable displacement pump. So, when the cabin temp gets cool enough if "de-strokes" the compressor, reducing it's output volume. Not to zero though - - just reduces it. If the AC is starting to freeze up, I suspect that even de-stroking the compressor may not stop the "cascade" of freezing.

I've had dozens of freeze-ups. It starts slowly. Eventually the evaporator is largely frozen up and the blower output drops way down. If I stopped, I would find the IHX (integrated heat exchanger) tube white with ice. The IHX is a secondary stage in the AC. The output from the evaporator super-cools the incoming (warm) refrigerant so it can get even cooler when it goes through the expansion valve. In addition, the warm fluid heats up the low-pressure gases from the evaporator. Because the high pressure gases going into the radiator/heat exchanger are hotter, the system is more efficient in removing heat from the system. That is great for cooling - - but only if the system is kept under control. When it gets into a runaway condition, it accellerates the problem
Gotcha. I was wondering how the system would work, it definetly seemed to be a smaller setup than my old truck. But having a secondary heat exchange stage would definetly up COP. Pretty trick little system. I also bet that when the compressor destrokes is when I can hear the flow in the condenser in the truck. If it's going that slow some of the liquid could be flashing before the expansion valve presumably... it vaguely reminds me of that.
 

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Took my 17 Denali in for the AC freeze up and this is what the service dept did to fix it !! Don't know if it's fixed as it worked ok most of the time and I haven't driven it enough to see if it will happen again . They also worked on my infotainment touch screen and it's on the same report for anyone interested !!
 

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@coolformula: Keep documentation of the problem. That way if there is a "fix" available after your warranty has expired, you can get it done at no cost. There is one software "tweak" being done that will likely stop it from freezing up >> which will eventually lead to it blowing warm air once the evaporator is encased in a block of ice. Perhaps there are other tweaks that will come available. I talked with a GM service mgr yesterday and he said that GM corporate is advising not to attempt any repairs at this time (if I understood him correctly) - - I think that he mentioned that he thinks that they will be coming out with some tweeks soon. But that is somewhat "Reading between the lines" and was my impression rather than fact.

In some states they have a "lemon law" whereby if you've taken it in 3 times for the same thing and they cannot fix it, they'll buy it back. I did that. I was only charged for the mileage up to the FIRST time that I brought it in. That was very generous. I'm appreciative.
 

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So at 31,000 miles and 4 years/8 months my A/C quit. Took it to dealer and was told they found no leaks but had to replace the compressor b/c the clutch failed to engage, even after a software update. Dealer asked GM and they said they would cover about 75% of cost. I had to pay for the compressor and diagnostic testing.
 

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I've noticed mine get warmer when it's hot out intermittently. When it does it seems to be linked to the active shutters. Sometimes in car reflections I can see them open back up when I stop and the air gets cooler again. When it's 105 out and I just got in the truck, you can notice it. When the cabin cools down I don't notice it too much. Similar to what you're noticing?
I would be concerned about the shutters, I don't think they are supposed to close when it's that warm out.
 

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I would be concerned about the shutters, I don't think they are supposed to close when it's that warm out.
I keep a pretty good eye on my temps, I haven't noticed any spiking per say. I'd imagine there is still enough air flow that it cools sufficiently. Seems to be normal operation as the tahoe behaves similarly with the only exception being that it won't get as cold.

I have been keeping an eye on it though.
 

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I keep a pretty good eye on my temps, I haven't noticed any spiking per say. I'd imagine there is still enough air flow that it cools sufficiently. Seems to be normal operation as the tahoe behaves similarly with the only exception being that it won't get as cold.

I have been keeping an eye on it though.
Doesn't seem right, if the AC isn't cold until the shutters open then it seems they should be open. Try looking up the normal operation of them if you like......
 

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On Tuesday I sold my 2017 Colorado to GM (lemon law buy-back because of unsolved AC issues). On Thursday I picked up my new 2019 Colorado. I've only driven it 30 miles, but the AC worked great. I say this because I stuck a digital thermometer probe about 6 inches into the vent and also used a "data logger" to record the temps. The vent temperature settled in at around 43 to 44 degrees. It stayed in a "Closed loop" mode, rather than drifitng down and out of control. The cold "overshoot" was minor (never got to a freezing condition) and it corrected itself about 2 to 3 times as fast as the previous version. The previous version would settle in at around 38 degrees. While that may seem reasonable to some people, keep in mind that the evaporator tubing and fins are colder than the air coming out of the vent. A reasonable estimate is that the tubing and fins are roughly 6 degrees colder than the air vent temp (but it depends on the blower speed). So with a vent temp of about 43 degrees, the evaporator tubing temp is about 37. A pretty safe temp.

It is surprising to me that there is so much variability between Colorado units. Some have problems and some don't.

The reason why I bought another Colorado (knowing that there are some deficiencies in the AC units) was (1) I love the truck and (2) I had about $3K invested in Colorado specific add-ons that I wanted to re-use.
 

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Doesn't seem right, if the AC isn't cold until the shutters open then it seems they should be open. Try looking up the normal operation of them if you like......
Well that's it... it's cold, just not as cold. Shutters closed air out the vent is 42. Shutters open around 36. On these cooler days... mid 80s you don't even notice it. I'm actually going up to the dealer today anyway so I'll bring it up and see what they say. It's not a huge swing... but you notice it if the cab isn't cool yet.

Edit: it would appear that mine operate exactly the opposite of what they are supposed to be doing.... interesting.
 
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