Solved heater problem 84 300D W123

SYMPTOMS:
- full heat all the time when temp dial anywhere but "MIN"
- heat coming from monovalve receiving no voltage
- full cold when in MIN detent / monovalve receiving voltage

SOLUTION:
Part number 0008221003 - the mystery box (on the W123, pull the glove box out and it's mounted above, ez to get to, one wiring harness plug and one screw)

- Junkyard pulls are all over ebay starting around $50.
- brinsonco.com has them for $115 reman by not-Programa w/three year warranty

Be aware that when other components upstream from this unit go bad, the problem can cascade downstream and burn out this box. These include the monovalve and the electric coolant boost pump. I checked my monovalve for resistance and it was 17, which was within the 11 to 19 acceptable range. I forget what the boost pump range is because I didn't check it...I put a new one on the car. ebay $90.

Tomorrow, refrigerant.

Spending too much money on this car.

Jim