126 Climate Control

[ken juul]

I've searched 30 pages of the archives, no luck. 91 300SE. The system seems to have a mind of it's own. It will work fine at start up, at some point, 30 min to an hour later, warm air will come out the center vents and the small upper side vent, the lower side vent will continue to have A/C. Rotate the temp control to minimum, 15-30 minutes later things return to normal. When the center vents are blowing warm, if the temp knob is rolled to heat, the floor vents open as expected, turning back to cold, floor vents close and center vents blow hot again. Blower acts normally, adjusting speed to try to attain the setting of the temp selector. Monovalve has been replaced, twice in the last 2 years. The overhead temp sensor test ok, the sensor fan works, the tube is intact. The temp sensor in the heater case tests good. All the fuses are ok, they were replaced about a year ago. Had a mityvac on the tubes at the vacuum contol manifold. All seemed to hold vacuum. The situation is further complicated by the airbag on the passenger side. Makes it hard to check operation of the servos. Does the dash need to come off to get to the servos? Any suggestions? Help! Wife is loosing faith if my DIY abilities!