2015 Tahoe also. I'm in Dallas. And on 100+ degree days it's total sh*t at idle before heatload has been removed or atleast it WAS for me (ive managed to improve it somewhat). After having the dealership replace a line, then the compressor and then condenser which they said were bad and recharge. It was certainly better but not great. The replacements were covered by carshield but they provided an aftermarket compressor which I replaced with a brand-new oem one on my own after the stealership told me the temps were within spec. Said 30-40 degrees vent temps cooler than ambient was best it was gonna get at idle... After the second compressor replacement it was better but still not great at idle.
Took it to another stealer ship and was told basically the same thing, within spec, blah blah blah.
One thing I did notice were the fan speeds like you AND 2 it did better if you would increase the rpms..
I believe all the issue has to do with the AI logic that controls the AC system.
1. Ai controls the variable ac compressor, and it constantly goes up and down (varying vent temps widly some times) trying to keep the evap temp between 3(37.4f) and 4(39.2f) degrees Celsius and im sure also varying to control head pressure. unfortunately vent temps after 20 mins when heat-load has been mostly removed are usually no lower than 46 going down the road but can vary all the way up to 54 especially at idle while the ai is varying compression on the system. (47-48f seems to be avg and acceptable and sometimes able to maintain that at idle after heat load has been removed). Would like to see AI logic try to keep the evap at a lower temp say 1-2c, like with my wifes 2021 terrain.
2. Ai controls the cooling fan speed. I've never seen the cooling fans commanded to anything higher than 60% with the ac on and at idle. And I've actually seen it command it to 10% (only when i have the ac blower motor set to 30% or below) which apparently is not enough of a amp draw to actually run my cooling fans so they shut off completely. Why AI isn't commanding the cooling fans to 100% when its 100+ degrees outside while its at idle or why it would ever command them to 10% while the ac is on is beyond me.... It's not providing enough air flow over the condenser to optimally function..
So what I did do that made a significant improvement was get a Diablo i3 tuner and increase idle speed from 450 to 950 at idle while in park only. This also had a benefit of the AI not commanding the cooling fans to only 10% when AC blower speed was set to less than 30% (im assuming the higher idle keeps the engine hotter and not allowing fans to be commanded to lower speeds). With the tuner I was also able to disable AFM/Dod, remove the speed limiter and program the transmission for a firm shift.
Starting to get hot here again in north Texas and had been doing pretty well this year, but now that we're having the 100+ degree days again. I was considering a auxiliary fan on the front of the condenser I could trigger with a fob for remote starts to cool it down after work and before I get in it. Possibly also a switch inside the cab to kick it on at low speeds or idling. Mounting looks like its going to be a PITA.
Had considered a relay on the ETC sensor wire to cut signal to the sensor there by tricking the ECM it into a fail safe mode and forcing it to kick on cooling fan speeds to 100% but failsafe mode also kicks off the ac compressor (so that's a no go).
And i just realized the other day the diablo tuner allows fan control at different temps. was considering putting fans to max at all temps for a easy temp fix until the summer is over but I'm getting error messages from the tuner, waiting on a email back from the techs at diablo.
Unfortunately the fans are pulse width modulated and there's no easy solution I can find to just kick em on to high manually because AI logic will not...
I think some of the issue with getting help and understanding on the issue is some ppl are just more warm blooded then others. I tell you I notice temp changes within 1-2 degrees the warmer the more uncomfortable I get.. My home ac is set to 68 degrees year round. I know ppl that leave their at 70-74, I would literally die if i had to live in that household with them... You tell someone on the board or the stealership that its blowing 50 degree air on a 100 degree day and they look at you like your crazy and you should be jumping for joy it blows that cold. I notice a huge difference in 46degree air and 50 degree air out of the vents (closer to 55 before increasing idle speed). And i know my Tahoe can get it there under the right conditions even on a 100+ degree day.
