A/C and Fan Speed

[Zortster99]

Hi Everyone.... Thanks for any help in advance.
I own a 2003 LTZ. I am having trouble with the "Auto" setting with the A/C. When I first bought it, if I set the thermostat to 60, the fan blew on hi (100%) and the air was very cold. If I set the unit above 60, the system provided the correct amount of cooling and fan speed based on conditions.
Now (I've had the TB about 10mos, 9800 miles) when I set the A/C to 60, even when it is 90 outside, the fan only blows about 60% of full. Other settings dont seem to work as well either when it is hot outside. For example, setting the AC at 67 when it is 95 outside does not cause the fan to blow at full.

I have had the TB in twice for this. I was told on my last visit that they called the Engineers at Chevy and this is "normal" operations. They supposedly even checked 4 other 2004's and said this is how they work.

Ayone else has this experience? Any hints on what is going on?

Thanks again for any help!

[markbair]

I am not sure if it is caused by the same thing, but my A/C SUCKED when I was sitting at a light or idle. I took it into the dealer and there is a service bulletin that was supposed to fix it. THey reprogrammed the HVAC computer with a new program from GM. Problem solved, the air even blows colder than it did before. Hope this helps. I don't have the bulletin number though, sorry.

[Zortster99]

Thanks for the info.

I am also looking for confirmation from other TB owners about how their A/C works. If it is hot outside (above 80) and the A/C is set to 67, does the fan blow at FULL? Does the vent ever change to RECIRCULATE (mine does not)?

Thanks again

[markbair]

AFTER they did the reprogramming it does blow full, and if it is really hot, then it switches to recirculate. It used to not do that. The reprogramming fixed a lot of my troubles. Go to your dealer, they should know that there is a service bulletin. He told me that the a/c in TB's are known to have trouble. Well, either way, my sick truck is cured....

[meyers95]

Originally Posted by Zortster99

Thanks for the info.

I am also looking for confirmation from other TB owners about how their A/C works. If it is hot outside (above 80) and the A/C is set to 67, does the fan blow at FULL? Does the vent ever change to RECIRCULATE (mine does not)?

Thanks again

My 03 tb blows full speed in the situation you explained above.

[Zortster99]

Thanks to all who are responding.

Great forum!

[dshow]

I have an '03 TB as well... When I first got it, the AC would not work sometimes and there was a TSB to replace a pressure sensor so now it works when I turn it on. However, it could be 200 deg outside and if I left the fan on low when I stop the engine, the fan stays on low when I start up again and it never switches to recirculate automatically. Is there a way to read back the calibration version number of the HVAC unit? Does anyone have a TSB number?

Thanks!

[Zortster99]

I cant remember the last time my system automatically switched to recirculate. I found another forum that said to press Front Defrost+Rear Defrost + Mode at the same time to force the sensor to read outside air.
Not much happenned when I did it.

85 outside today. I set the A/C to 66. Fan blew at about 80% with no recirculate. I still cant believe this is the way "its supposed to work!"

[dshow]

This is probably a really stupid question... But what is the proper way to turn on the AC in Auto mode? If the system is turned off and I want to turn it on, if I adjust the fan speed, it turns on but in manual mode... The only way I've found is to bump the temperature up or down... anything else puts it in manual mode.

Also, does auto mode control which vents the air comes out of?

[Zortster99]

The only way to put it in AUTO mode is to press the AUTO button. Changing the TEMP lets the system remain in auto mode. Changing fan speed or selecting the MODE button (which only changes the vents air flows from) will take the system out of AUTO mode.