Frustrating Heat issue Part Deaux

[mikeran]

Ok please for those who will offer teh quick answers.
1. Yes I have read and done everything in Clarks Garage, the clips are in place.

For everyone else A while back I had constant heat but the clips were fine. followed all the troubleshooting guides I could find and replaced the following parts

Heater control valve
All new vacuum lines
Known Good HVAC controller
New HVAC vacuum check valve

Yet still the heater valve would not close, kept at it and finally discovered a bad wire in the wiring harness, changed the wiring harness and everything worked fine, Heat/AC everything.

Fast forward to the other day and guess what? Again the heater valve will not close. I am totally lost as to what could be the problem now and would welcome any no matter how strange thoughts or ideas.

All the servos check out good as per the Shop manual
All the sensors check out good as per the shop manual

While the car never closes the valve when we check it sitting in the driveway, my son says sometimes when he's driving it cycles on and off HOT to AC to HOT to AC

For now I rerouted a vacuum line to at least let him drive without full heat but he really needs the AC working.

HELP!!!

thanks in advance and major kudos or beer to the person how can solve my problem