2015 AC Only Cold When Driving

[Chuck 2015 Tahoe]

I live in south Texas so heat is no joke. Been over 100° the last few days. AC only cools when driving. I noticed that my cooling fans only spin at a moderate to low speed. My previous Tahoe, 2013, you could hear the fans kick into high gear. This newer 2015, never does that. Blows hot air when at idle. Refrigerant level is spot on and compressor clutch spins fine (but does not cycle off and on). Pulled fan fuses and as soon as I put them back in, the driver's side fan went on high for about 10 seconds then back to low speed. Wanted to see if anyone has any ideas before I take it to a shop and start dishing out money.

 

[Sparksalot]

I live in south Texas so heat is no joke. Been over 100° the last few days. AC only cools when driving. I noticed that my cooling fans only spin at a moderate to low speed. My previous Tahoe, 2013, you could hear the fans kick into high gear. This newer 2015, never does that. Blows hot air when at idle. Refrigerant level is spot on and compressor clutch spins fine (but does not cycle off and on). Pulled fan fuses and as soon as I put them back in, the driver's side fan went on high for about 10 seconds then back to low speed. Wanted to see if anyone has any ideas before I take it to a shop and start dishing out money.

Have you replaced the cabin air filter recently? I’ve noticed a similar thing with only a dirty filter.

 

[vf1000ride]

From the electrical manual I have on our trucks the fans use the A/C pressure sensor to vary fan speed through the engine ECM once it reaches a set pressure. Your A/C pressure sensor may be funky, it's a three wire setup per the wire prints. I would say if you have already verified the system charge it might be worth trying the pressure sensor. If it is showing that it meets minimum pressure it won't cycle the clutch but if it doesn't report a higher, more heat saturated pressure, it may not kick the fans up to high.

 

[swathdiver]

You are probably low on refrigerant. Gotta get it hooked up to a manifold. Check the relays to the fans, there are 3 on the previous generation, not sure about yours.

 

[Matthew Jeschke]

It should be cycling on and off... UNLESS controller see's it's low on refrigerant. My guess is you have a leak somewhere.

 

[travisk]

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.

 

[sb38646]

I live in south Texas so heat is no joke. Been over 100° the last few days. AC only cools when driving. I noticed that my cooling fans only spin at a moderate to low speed. My previous Tahoe, 2013, you could hear the fans kick into high gear. This newer 2015, never does that. Blows hot air when at idle. Refrigerant level is spot on and compressor clutch spins fine (but does not cycle off and on). Pulled fan fuses and as soon as I put them back in, the driver's side fan went on high for about 10 seconds then back to low speed. Wanted to see if anyone has any ideas before I take it to a shop and start dishing out money.

Im needing help too. Maybe my input can help. My tahoe has always done this unless im going fast. Used to i could do this an actually idle for a while. There is a trick that seems to work or used to even while at idle. Turn rear ac and front ac all the way up. Turn back ac off first then front. Then turn front on second making sure both are on high.May take 4 or 5 tries. Back ac has to kick on first . My problem did get more problematic after i had my transmission rebuilt. (Not that that was a trigger) but they also reprogrammed it so that it doesnt got into 4cyl mode . Which is i guess like a tuner yet it didnt help me infact i think its worse bc now i cant idle with my tricks and it blow cold. Another thing i just noticed while trying different stuff is that it was blowing hot while driving so i decided to cut recirculate off and ac was much cooler with it off then it gradually got cooler and i turned recirculate back on and it was ice cold. Thats not normal right ? Letting outside air in and my ac worked better.

 

[blondie70]

Mine gets much cooler with recirculate on (no outside air).

 

[sb38646]

I live in south Texas so heat is no joke. Been over 100° the last few days. AC only cools when driving. I noticed that my cooling fans only spin at a moderate to low speed. My previous Tahoe, 2013, you could hear the fans kick into high gear. This newer 2015, never does that. Blows hot air when at idle. Refrigerant level is spot on and compressor clutch spins fine (but does not cycle off and on). Pulled fan fuses and as soon as I put them back in, the driver's side fan went on high for about 10 seconds then back to low speed. Wanted to see if anyone has any ideas before I take it to a shop and start dishing out money.

Mine gets much cooler with recirculate on (no outside air).

Yes, mine too when its working properly, but when its not the ac without recirculate is cooler. I know its crazy right ? I got a cabin filter yesterday. Im gonna try to get it in today if time allows.

 

[Jeff_]

After chasing a/c issues for over a year on my other vehicle, I'd suggest taking it to a reputable a/c repair shop and paying ~$150 for them to diagnose the issue and then either pay them to repair it, or repair the part yourself (if capable).

To me, I finally gave up and paid a shop diagnose the issue on my Camaro and then I bought the parts and repaired it all myself. Hindsight is 20/20.

 

[sb38646]

Cabin filter

After chasing a/c issues for over a year on my other vehicle, I'd suggest taking it to a reputable a/c repair shop and paying ~$150 for them to diagnose the issue and then either pay them to repair it, or repair the part yourself (if capable).

To me, I finally gave up and paid a shop diagnose the issue on my Camaro and then I bought the parts and repaired it all myself. Hindsight is 20/20.

Well cabin filter did not fix my issue. I live in rural Ms so no dealership for 30 miles and then they are iffy. Memphis would be my best option (an hr away). Local shops have found no issue with ac. Its charged . Compressor and fan works . And it blows cold if u can afford the speeding tickets.

 

[Geotrash]

Yes, mine too when its working properly, but when its not the ac without recirculate is cooler. I know its crazy right ? I got a cabin filter yesterday. Im gonna try to get it in today if time allows.

Had a similar problem with another vehicle a couple of years ago. Turned out to be low on refrigerant. I used the gauges James shows above to determine the pressures I was seeing vs what I should be seeing at the current ambient temps outside per the standard r134a tables widely available. I was able to add about half a can of refrigerant to get the pressures back in spec.

I know you said that the local shop said it's charged, but did they really put the gauges on it? I would take it to the closest local shop with a set of gauges and start there.