Cadillac Repair: 2000 Eldorado Inaccurate Temp Control, bumper to bumper warranty, temperature data logger

Question
2000 Eldorado Cadillac ETC with 50K miles.  I've had the car for about 2 years and the temperature control has never worked properly.  It doesn't maintain the correct cabin temperature.  The system has been checked over by the local Cadillac dealer who found it low on gas twice but claims that the temperature control is working "as designed." The car has been under the Cadillac certified used car warranty which extends the original bumper to bumper warranty out to 6 years or 100,000 miles

To prove that the car has a problem I purchased an electronic temperature data logger and suspended it between the two front seats at approximately chest level and recorded the cabin temperature during an hour and fifteen minute freeway trip when the outdoor temperature was 81 degrees.  Traffic was light and I was able to maintain a consistent 55 to 65 mph.  In spite of the fact that I had the setpoint at 66 degrees, the lowest the cabin temperature ever got down to was 69 degrees. It took about 25 minutes to drop down to 70 degrees and another 20 minutes to drop down to 69 where it bottomed out.  The fan speed started out at maximum and continued to drop and the discharge air temperature started out very cold and modulated back to cool as the trip progressed. From this I believe that the system is capable of providing the correct cabin temperature it's just that there is a problem with one of the components in the control system.

Incidentally, 69 degrees was comfortable due to the fact that I was wearing shorts and a short sleeved shirt.  Unfortunately, when I'm dressed for business 69 degrees is not comfortable. If I could just set the temperature setpoint to say 63 degreees to get 66 in the cabin the problem would be solved.  Unfortunately Cadillac for some odd reason designed the system so that it cannot be set below 65.  The next lowest "setting" is 60 but then the system runs wild at maximum cooling and fan speed.

It looks to me that either the system needs to be adjusted to correct for the 3 degree error (which the dealer says is not possible) or the temperature sensor, or temperature controller it’s connected to, needs to be replaced which they have so far refused to do.

Any other ideas?

Thanks

Answer
What you need to do is set the AC on 65 degrees on the control panel and set the fan speed to LOW SPEED.

Take an analog or digital thermometer and insert it into the center outlet vents and see just how LOW the temperature reading will go and let me know what you get after about 15 minutes of running on LOW SPEED.


tom