A/C vent air problem 2005 Sedona

I have a 2005 Kia Sedona, we were having what we thought were A/C problems, the air would go from freezing cold to barely cool and then after about minute go cold again. We took it to dealership and they checked freon and it was good, they ofcourse couldnt get the problem to repeat. It has done it off and on for a year now. The other day we were running just vent air, no A/C on, the vent air does the same thing. It goes from cool air to warm air then back again. I am thinking it must be some kind of thermostat type switch or something of that nature. Any advice would be greatly appreciated. Thanks a lot.

You can do one of two things, disconnect both terminals on the battery and put them together (WHILE DISCONNECTED FROM THE BATTERY NOT CONNECTED TO THE BATTERY!!!!) for 5 minutes and then reconnect them. OR you can remove the heater control head and disconnect it for 5-10 minutes. It is a fairly common problem, the control head for the HVAC gets an error and you have to reset it. We used to replace em but it won't fix the problem. Resetting it will fix it for awhile but it may or may not happen again.