Climate Control, '81 300D

Now that I am driving my daughter's fresh engined 300D I am much more aware of the climate control problem.

It acts like the cabin temp sensor is lagging in temp change. It will heat like crazy, then when it finally stops heating it blows cold for ages until you're freezing or you decide to shut it off. Is the temp sensor right there at the little square grill in the top middle of the dash, or is there a tube that goes down to the sensor in a remote location like an SD?

Does anyone know the resistance of a properly working sensor so I can test it once I find it?

Any suggestions or ideas will be greatly appreciated.

Have a great day,