The infamous Remote Control Thermostat installed in the 2005 -2006 model Montanas was a great idea gone wrong. They were notorious for their erratic set points (+/- 10 degrees was common) and their propensity to turn on the heater and the A/C at the same time.
The solution is to replace the Remote Thermostat with the Climate Control Center (CCC) thermostat. Montana and Dometic usually did this for no charge back in the day. I suspect you will have to buy it yourself today for about $200. The change over isn't too difficult.
Everything you ever wanted to know about this topic (Part Numbers, installation instructions, photos, etc.) can be found in by clicking on the following link to a 34 page discussion on this POS. A Search will uncover many more discussions.
http://www.montanaowners.com/forums/...ead.php?t=8145