W126

I own a 1982 300 SD. Among the few things I would like to fix is the intermitent heater. I have read about many possible problems, ranging from a faulty climate control unit, to bad brushes on the blower motor, to a faulty amibent temp sensor. Is there a way to tell what the problem is for sure before I tear in? The blower usually comes on when the car is first started (not always), then usually shuts off with in a few minutes (again not always.) The temp wheel usually sets the temp of the air comming out (once the motor has warmed up), Since it has been cold, it has been blowing warm air (when it blows.) The selecter buttons work great. A direction would be appreciated.

I have 1982 300SD with about 250K and a 1987 300SDL with about 400K on original engine. Same problem with each. Get excessive tire wear on inside of rear tires. Have replaced axles, rear wheel bearings, spring seats and installed HD Bilstein shocks. Problem is improved but still get wear inside. Do not carry excess weight in trunk.