Intermittent uncontrolable heat '98 ML320

[riske]

The temperature of the air coming from the vents in my ML320 is out of control. It cycles intermittently from hot to luke warm when the dial setting is on cold. It usually ends up as hot and stays there regardless of the dial setting.
IN AN OLD THREAD , MB DOC said........"Welcolme......
The early ML uses a blend air system..no heater valve. Also no diagnostic abilities on that early system.

There are 4 possibilities for your problem..YOU will have a hard time trying to figure out which one will rectify the problem.

The in-car temp sensor
the control unit in dash
the blend air motor &
the blend air control unit.

ANY of those could cause an intermittent problem like you are having...."

MY QUESTION IS:
How can I diagnose which component is causing the problem?
THANKS