I've got a 95 Bonneville. This system was not working correctly, when you would put the air on, it would be blazing hot and if you put the heat on, it would come out freezing cold. In order to make these work properly, I had to shut the car off and re-start it and maybe after doing this 5 or more times, then it would start working properly. Well, over the summer, we tried to put a new brain box in (whatever it is called it was located under the glove box) This did nothing, except now after putting the old one back in and trying to move some switches around on it with no success, whenever I get in the car, the ext. temp. says 90 and then the temp. read out just goes away and I never get any heat no matter how many times I shut the car off and re-start it. Has this happened to anyone else here?? I guess I can live with it, but driving to work when it'* one below zero today was not something I enjoyed. Thanks .

What year is your car? Please add your trim level and year to your signature. It will help us help you!

Sounds like ECC for sure.... In 95.

We'd need to walk you through the troubleshooting map.

You could start here...sorry for the long read ( I am supposed to write-up a techinfo on this and still haven't done it ).

http://www.bonnevilleclub.com/forum/...&highlight=ecc

Many parts could lead to the problem your having, but since you tried replacing the "box" (HVAC programmer), I am thinking it is related to the airmix door or it'* actuator, or the ECC control unit (the part you see on the dash). I'll need to check to see if anything special needs to be done when you swap the HVAC programmer. Swapping to a different one and back to the old one may have resulted in a loss of data that has now caused your display to not "recognize" the information leading to the wierd readings and behavior.