Intermittent a/c failure on a 2005 Tahoe manual controls

ORVietVet · Aug 17, 2025

Widow of an A/L friend of mine with a 2005 Tahoe LS with the manual HVAC controls. Problem: Intermittently the a/c will be on and then blow warm. Intermittently the a/c will not even turn on and then will kick on while driving.

Attached gauges at shop for intermittent a/c problem. This is the same 2005 Tahoe I did the exhaust manifold clamps on recently. Drove to pick her up and was ice cold and 1/2 way there, started blowing warm till got to her house. Shut off. She got in. Drove back to my house and a/c worked the whole way.

At shop today.....Ambient temp at 84 degrees.....29 degrees out the vent..... low pressure at 25 psi and high pressure at 200 psi.....system working normal..

Found 2 history codes: B0408-Temperature Control 1 Circuit Malfunction & B0418-Temperature Control 2 Circuit.

ORVietVet · Aug 17, 2025

I am looking for the Genuine GM or AC Delco part numbers for that control module and the actuator that controls the hot/cold mode. VIN is 1GNEK13T45R142468.

Her a/c can be ice cold and while driving will go to warm, without touching temp controls. When I run it, I can change the temp controls and can hear a loud ratcheting noise as the actuator change positions and sounds like is behind the glove box area. I believe the actuator is failed/failing and the control head has problems because the system is full and when it turns warm, the a/c clutch is disengaged and jumping the low pressure cycling switch does not engage the clutch. The ratcheting noise has been going on for quite a while, even though the a/c would blow cold. Now the noise is still there and the signal is not even at the low pressure switch at the accumulator I tried crossing the connections and still no clutch engagement. The other actuator controls for the modes of blowing out of dash, floor, both or defrost, all work for the direction of flow. When those are operated there is no ratcheting noise.

ORVietVet · Aug 17, 2025

She showed up the other day with it ice cold and while I was doing a live data search and she moved the hot/cold slides, it started staying hot/warm. I tried a reset and no help and like I said, there was a ratcheting noise at the glove box area when moved the hot cold slides but no noise when changing the modes for direction control.

ORVietVet · Aug 17, 2025

Mode door actuator is above the gas pedal.

D/S hot/cold actuator is center area above the transmission hump.

P/S hot cold actuator is under dash cover above the glove box and to the left of the heater core hump at top of HVAC box.

Recirc actuator is under dash cover and to the right and at the firewall area of the HVAC box.

ORVietVet · Aug 17, 2025

This morning I swapped the A/C compressor relay with the horn relay and still was able to duplicate the problem. I then removed the relay and jumped from pin 30 to pin 87 and the compressor came on and stayed on and the temp control went from cold to hot and back. IMO, the control head in dash is the culprit of her problems.

bigdogYJ · Aug 18, 2025

ORVietVet said:
This morning I swapped the A/C compressor relay with the horn relay and still was able to duplicate the problem. I then removed the relay and jumped from pin 30 to pin 87 and the compressor came on and stayed on and the temp control went from cold to hot and back. IMO, the control head in dash is the culprit of her problems.

Do you have a scan tool that reads actuator counts? Like a tech2? I know those systems work on command counts and actual counts as the units to specify their position. It would be helpful to compare those to confirm the control head is truly giving erroneous commands to the actuators or if the actuator is drifting and getting stuck. Something to consider for diagnostics sake.

ORVietVet · Aug 18, 2025

bigdogYJ said:
Do you have a scan tool that reads actuator counts? Like a tech2? I know those systems work on command counts and actual counts as the units to specify their position. It would be helpful to compare those to confirm the control head is truly giving erroneous commands to the actuators or if the actuator is drifting and getting stuck. Something to consider for diagnostics sake.

Yes. I have a Foxwell NT710 GM specific scanner and I did monitor counts at the actuators and the noisy right side actuator was not smooth, like the left, when switching from hot/warm to cold. It was slow and erratic and even when it was finished getting to it's commanded position, it was still "hunting" and that actuator was noisy/ratcheting while moving. The problem is the control head command to the compressor to actually activate the clutch. It just stops intermittently and if I jump the #30 and #87 pins, at the relay, it works and blows cold. The compressor just shuts down intermittently/randomly or does not even come on at all. If it is refusing to come on, the relay jump always turns it on and she has cold air. I am going to confer with my shop owner buddy this morning and make a decision. I know she needs the actuator. It will open and close but is ratchety and noisy.

bigdogYJ · Aug 18, 2025

Got it. Wasn’t sure how far you got in diagnosing the command vs actual. Sounds plausible that the control head could be the culprit. I guess you could confirm that the control wire for the relay is getting lit up or not, can’t remember if it’s ground controlled or bat +. But that would confirm no signal from control head.

As a side note (and not sure how much programming is available for the manual control head) but my 04 Yukon xl with auto HVAC had an issue where it would not go into recirc mode. The button indicator would light up but watching the command and actual counts they wouldn’t move. Everyone I conferred with condemned the control head. Since I had an active subscription for that VIN on GM tech connect, I just reflashed my control head. Recirc started working and continues to function today, 2 years later. Again, not sure what amount of programming, if any, is available for the manual control head but something to consider. Good luck.

stutaeng · Aug 18, 2025

Also check that little thermometer on the driver's side headliner. My 06 had this condition where it only blew cold air at the lowest setting, any other temperature was not really cold. Similarly, on the hot setting: wasn't really hot until I hit the hottest temperature, then it was 100% hot full blast.

I was about to replace the HVAC module, but somehow came across an thread on the TYF. That thermometer has this little fan and mine was basically seized. I replaced it and everything works fine now. It's GM Genuine part #22834330.

ORVietVet · Aug 18, 2025

stutaeng said:
Also check that little thermometer on the driver's side headliner. My 06 had this condition where it only blew cold air at the lowest setting, any other temperature was not really cold. Similarly, on the hot setting: wasn't really hot until I hit the hottest temperature, then it was 100% hot full blast.

I was about to replace the HVAC module, but somehow came across an thread on the TYF. That thermometer has this little fan and mine was basically seized. I replaced it and everything works fine now. It's GM Genuine part #22834330.

Thank you.

ORVietVet · Aug 18, 2025

bigdogYJ said:
Got it. Wasn’t sure how far you got in diagnosing the command vs actual. Sounds plausible that the control head could be the culprit. I guess you could confirm that the control wire for the relay is getting lit up or not, can’t remember if it’s ground controlled or bat +. But that would confirm no signal from control head.

As a side note (and not sure how much programming is available for the manual control head) but my 04 Yukon xl with auto HVAC had an issue where it would not go into recirc mode. The button indicator would light up but watching the command and actual counts they wouldn’t move. Everyone I conferred with condemned the control head. Since I had an active subscription for that VIN on GM tech connect, I just reflashed my control head. Recirc started working and continues to function today, 2 years later. Again, not sure what amount of programming, if any, is available for the manual control head but something to consider. Good luck.

I think I said it but unsure. I did a reset and there was a message of, "No Response Returned By Control Module".

ORVietVet · Aug 21, 2025

I work as a part time service writer at my friend's shop in Junction City, Oregon. He is a specialist in so many fields and has done work on this Tahoe before. He used his Snap On gauges and reported to me what the readings were. No charge for the inspection. It was working when he inspected.

This morning she came in at 9 a.m. and I cleared the codes in the system. She did not use the a/c to get to shop. Was still in the low 60's. B0408 and B0418. I then did a re-calibrate on it.

Shut the engine off. Moved the manual temp controls up from bottom to about 3/4" up. Turned fan speed switch to 3. Removed the 10 amp HVAC/ECAS fuse, from the under hood fuse/relay box, for 1 minute. Put the fuse back in and then started the truck and let run for 2 minutes. Shut truck off. Let the truck sit for about 15-20 seconds and then restarted. Then something strange happened that had never happened before during this ordeal she has been having. Instead of having either all cold out of all four vents of the D/S and P/S, it blew cold on D/S and hot on P/S. No matter what I did by shutting off the system and shutting off engine, on a restart and set for a/c to work, it blew cold on D/S and warm on P/S.

Then I did the re-calibrate again and we got surprised again. Everything worked as is intended. Blew cold when commanded to and warm when commanded to and was same for both the D/S and the P/S. In other words, it acted like there was never a problem. She drove home and the a/c worked great the whole way. She is gonna monitor it during the day because she will be using the a/c today in 90 degree weather.

ORVietVet · Aug 21, 2025

We know the temp actuator, on the passenger side is failing, simply because it makes the ratcheting noise, during movement. That actuator's problem, was admitted to from the beginning. That does not explain how the compressor was shutting down and causing the whole system to blow warm air, when set to cold.

During the calibration process today, the left temp actuator, located above the transmission hump, was working fine and was blowing cold when, after the first calibration attempt I had cold on the left and warm on the right. Then a second calibration caused both sides to blow cold and then warm when commanded to.

I still believe that the first calibration did show the weakness of the right-p/s temp actuator and then it decided to work after a 2nd calibration attempt. BUT, I would bet she will experience a warm out of both and a compressor clutch not engaging, sometime down the road.

ORVietVet · Aug 22, 2025

As far as I can tell and find during info searches and with input from my friend, a well known electrical specialist in the industry, there is no limp mode. I believe that with the strong possibility of the control head causing the intermittent shut down of the compressor clutch and easier to replace, we are going to likely do the control head replacement first. The cold on the left and warm on right was the very first time that happened and after 2nd calibration, did not happen again. She will monitor and report back. We have some 90+ temps the next few days and she will have plenty of times for using the a/c.