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Discussion Starter #1
I noticed today while driving around town, about 30-35 mph, that about every 30-60 seconds, the air temperature coming out of the vents got considerably warmer. These variations only lasted a few seconds or so and then went back to being cold again, only to be repeated over and over. I also got the distinct odor of stale air every time this happened, which also subsided until the next cycle. These did not seem to correspond to acceleration or braking, or any other driving condition. It was sunny and 76 degrees today.

Anyone else have this sort of thing going on?

Tony
 

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I haven't noticed such an event on my car, but that doesn't mean that it is not happening. I will check more closely the next time I drive it.

The stale odor of the air that comes out of the AC vents is probably due to the high moisture content that results when the air is not cooled during the time that the AC is shut off. Most people don't know that prior to our current emphasis on "green," the AC would run even when the temperature was low and the air was being heated. The purpose was to dehumidify the air before it was heated. Now, who knows? Perhaps your event is one way GM is trying to get the corporate average fuel mileage up (by periodically disabling the AC). Or it might be that the temperature setting is so close to the outside ambient, the AC system periodically thinks it has cooled the interior sufficiently. In any case, 76 degrees is pretty low and most people in this part of the country would not even bother turning on the AC at that temperature.

I am scheduled to take my car in for the "radio does not stay off" fix tomorrow. When I take it out this afternoon, I will check the AC operation and if I don't experience your problem, I will question the dealer as to exactly what his CD with the new software changes.
 

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II am scheduled to take my car in for the "radio does not stay off" fix tomorrow. When I take it out this afternoon, I will check the AC operation and if I don't experience your problem, I will question the dealer as to exactly what his CD with the new software changes.
My dealer still has not fixed my "radio on/off" problem. If yours does, would you please share as much information as you can so that I can educate my dealer? Thanks.
 

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I experienced the radio not staying off the other day. I thought my car was possessed. Fortunately I never turn it off.

My AC cuts off on WOT but I think that is something wait4me did in his tune.
 

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Tony407,
I think when you have the A/C on AUTO, it will cycle the A/C unit on and off periodically when your temp setting is reached. It'll try and maintain your temp set point using ambient air as well as A/C. tedcmiller explained the stale air smell with the higher humidity when not using A/C.
If you put the A/C on manual (ie. always ON), then I don't think that the system cycles on and off as it does in AUTO mode. I'll have to try it to confirm, though.
 

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CTS-V 2009 White Diamond, 996TT Silver, G35 Coupe 6mt, M45S
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The stale air is caused by mold. Mold grows on the bottom of your a/c where all the dirt collects. When the a/c is on, water is extracted and is dripping down and collecting at the bottom of the a/c. Covering the dirt and mold. Once the A/C is turned off, it will start drying up and smells from the wet dirt/mold go into the cabin. If it's very humid outside those smells will keep going without the a/c, because the mold stays active in humid air. And when the car is turned off, the mold has it's new supply of water at the bottom of the a/c and happily starts growing.

I found a simple way to clean the bottom of the a/c and kill the mold. I'm very allergic to mold so I have to do it on a regular basis. I take a mixture of Lysol all purpose cleaner (lemon scented 4-1 dilutable, make sure it's got Alkyl ammonium chlorides as an ingredient) and water and put it in a garden sprayer. Remove the cabin filter (under the hood by passenger windshield) and spray the solution directly into the air intake. I spray it in first without the fan running, let it sit a bit and then turn on the a/c fan (don't turn on the engine) and spray some more.

You might get some solution coming from under the dash on the passenger side. The a/c is designed to deal with water so nothing will get hurt in the process. I put a towel on the passenger foot area to catch any overflow.
Let it sit if 10-15 minutes. That's how long it takes for the chlorides to kill the mold. You can still have some water come out after you drive the car through a corner.
After it's done, you''l get a nice fresh smell coming out of your A/C. The lemon smell won't last too long. You don't need to put a whole lot of lysol in the solution. A mixture of 1 to 10 will do.

When I first got the car, it had been test driven quite a lot (138 miles worth). When the temperature here in Texas started to rise and i turned on the a/c, there was a *whole* lot of mold coming out of the a/c. I don't if it was the test driving or during manufacturing, but it took me a while to get rid of the mold. The cabin filter only filters outside air, so it's easy for mold to get into the a/c from inside from all those dirty passengers shoes.

Hans.
 

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Discussion Starter #7
Thanks, everyone. I'm used to the "mold" smell in other cars I've owned when I switch off the AC after using it for a while. That's acceptable to me, as I don't get the smell when the AC is running. However, I certainly don't want the AC cycling off and on as much as it does and getting the smell just as many times! And I did not have it on AUTO. I had set the temp to 72 and set the fan speed and vent distribution manually. Maybe I will try to leave it on AUTO and see if it still does it.

I certainly hope GM didn't design the V so that this is normal!! Because every car I've owned up until this point with auto climate control doesn't cycle the AC on and off, it simply modulates the temperature and/or fan speed & vent pattern to achieve the desired temp (unless you're in manual mode.) That way, you don't get stale air blowing into the cabin.

Besides, even without the smell, there's a definite temperature drop as well - every 30 or 60 seconds.

Tony
 

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Toney407,
I completed my drive this afternoon and noticed no peculiarities with the AC even though it was in Auto mode. I might mention that in years past, the flow of refrigerant to the AC evaporator was controlled by a special valve that kept the temperature of the evaporator above 32 degrees so that it would not freeze up. Later on, as compressor clutch life went up, the valve was eliminated as a cost saving and the compressor was cycled on and off to avoid freezing up the evaporator. I don't know what scheme they use today, but I would say that you have some sort of problem. Based on your description, it sounds like the compressor is being disengaged for a period of time that allows the evaporator to get excessively warm. This should not be happening.
 

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Discussion Starter #9
Toney407,
I completed my drive this afternoon and noticed no peculiarities with the AC even though it was in Auto mode. I might mention that in years past, the flow of refrigerant to the AC evaporator was controlled by a special valve that kept the temperature of the evaporator above 32 degrees so that it would not freeze up. Later on, as compressor clutch life went up, the valve was eliminated as a cost saving and the compressor was cycled on and off to avoid freezing up the evaporator. I don't know what scheme they use today, but I would say that you have some sort of problem. Based on your description, it sounds like the compressor is being disengaged for a period of time that allows the evaporator to get excessively warm. This should not be happening.
Thanks for taking the time to do this. I appreciate it. I'll mention the problem to my dealer and see what they say.

Tony
 

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I drove the car again this morning both to the dealer for the radio fix and then home again after the fix was installed and I did not notice any peculuarities in the operation of the AC in Auto mode either going to the dealer or returning from the dealer.

For JFJr: The fix for the radio seems to work fine. It will come back on if left on when the car is shut down, but no longer comes back on during start up if turned off manually before turning the car off. There are apparently no other changes or negative affects associated with this fix. This problem was discussed at length in a thread on this forum called "Electrical glitches with new CTS-V." In that thread ewill3rd gave the TSB number for this problem as 08-08-44-019A. This is the same number that appeared on my warranty sheet describing the work that was done. If you look up this TSB on the Internet, it gives the CD part number as 20833568.

It should be noted that althought the radio is off, the pop-up screen still pops up when the ignition is switched to "Run." The radio does not turn on, but the outside temperature is displayed in the upper right corner. The navigation system also does not work if the radio is off.
 

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...It should be noted that althought the radio is off, the pop-up screen still pops up when the ignition is switched to "Run."...
Mine does not do this unless it was up when I switched the car off. If it was down, it stays down when I start up the next time.
 

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Yes, the screen pops up only if it was up when the ignition was turned off. If it was put in the down position, by use of the dash button, before the ignition is switched off, it stays down when the ignition is switched back on. However, the Cadillac wreath and shield appears on the screen in either the up or down position. I was aware of the difference, but I did not feel the need to describe both situations.
 

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Not sure if this will help.

I went on the TIS website, inserted my VIN and selected the ECM

http://tis2web.service.gm.com/tis2web

Detailed history:

1 12632176 New software to improve A/C performance.
2 12633627 New calibration with diagnostic enhancements for DTCs P0171, and P0174.
3 12632177 New calibration with diagnostic enhancements for DTC P0461.
4 12629302 Speedometer
5 12634489 New calibration with diagnostic enhancements for DTC P0300.
6 12633608 New calibration with diagnostic enhancements for DTCs P0171, and P0174.
7 12625997 Slave Operating System
8 12629291 Engine


Seems like they have some A/C updates?

Hans
 
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