KLVN

On page 1-29 of your User Manual is the procedure for clearing the CMOS memory. Once you find the right thingy on the motherboard, it's a simple matter of moving the cap from pins 1&2 to pins 2&3 for about ten seconds. You then put the cap back on pins 1&2. I also replaced the CMOS battery as a precaution.

I recently experienced the same thing. The Air Conditioning Auto mode would fail and then the autopilot would stop working correctly. Earlier this year I built a new computer and used the ASUS Z87-Pro motherboard. About two months after I started using the new computer, the system time stopped being correct. I learned from several different forums that clock problems are fairly common on ASUS MBs. I contacted PMDG and Ryan indicated that they make extensive use of the internal system clock and are very aware of the ASUS clock issues. Some of the symptoms that you and I experienced are well known to them; however, I was apparently the first to directly report autopilot problems. I downloaded and installed the latest BIOS and cleaned out the CMOS memory using the jumper procedure in the ASUS user guide. I have had no clock issues and no problems with PMDG airplanes since then. It might be worth looking at the system clock as the culprit in your case.

Do you have an ASUS motherboard?

For this you need an appreciation of the cartoon character Tweety Bird...On the RNAV(GPS) 16 at KPSM the waypints are ITAWT ITAWA PUDYE TTATT IDEED