Toyota Repair: Hot Air Coming From Air Vents While the ACs On, diagnostic mode, factory warranty

Question
On my 2006 XLE Sienna the air coming from the front air vents remains hot until you switch the temperature down to lowest temperature. Once you set it to low, the A/C will run you out of the van. It you then bump the temperature up one notch, to 65, the air will turn hot again (while on A/C). This happens on both the drivers and passengers side of the van. I haven't checked the rear climate controls to see what happens in the back. This first happened while we were in Texas for Christmas and were going to take the van to dealership down there but it started working again. I figured it wouldn't be worth our time if it's working because they wouldn't be able to identify the issue. The problem has once again popped up it ugly head and our local dealership has being looking at the van for a day with on good solution. I'm just curious it anybody else has experience this type of issue and if so, what was done to resolve it. Thanks!

Answer
No I have not encountered this problem before, there may be a problem with the auto A/C control panel which has the climate control computer installed,whatever it is should still be covered under the factory warranty. This auto air sytem also has self diagnostics built in, the dealer should know how to put the system in diagnostic mode so that the trouble area can be located.I'm assuming it has auto air since it's an XLE.