Have a 2004 TL that seems to have a mind of its own when running the heater/ AC. The temperature settings seem to make no sense. When we try to get heat , you need to crank it up to 28+ or else the AC comes on. The auto setting doesn't seem to keep a constatn temp. Any one else with this issue?

The temperature you set to is what you want the cabin to be. In other cases, when you set a temperature, the rate/temperature of the air will vary depending on your position with the sun. It is just a mechanism installed into the TL that will allow better warming/cooling of the cabin

Also in full auto mode, the compressor is ALWAYS on, just to varying degrees.